Termbank
  1. A
    1. Abstraction
    2. Alias
    3. Argument
    4. Array
  2. B
    1. Binary code file
    2. Binary number
    3. Bit
    4. Bitwise negation
    5. Bitwise operation
    6. Byte
  3. C
    1. C library
    2. C-function
    3. C-variable
    4. Character
    5. Code block
    6. Comment
    7. Compiler
    8. Complement
    9. Conditional statement
    10. Conditional structure
    11. Control structure
  4. D
    1. Data structure
    2. Duck typing
  5. E
    1. Error message
    2. Exception
  6. F
    1. Flag
    2. Float
  7. H
    1. Header file
    2. Headers
    3. Hexadecimal
  8. I
    1. Immutable
    2. Initialization
    3. Instruction
    4. Integer
    5. Interpreter
    6. Introduction
    7. Iteroitava
  9. K
    1. Keyword
  10. L
    1. Library
    2. Logical operation
  11. M
    1. Machine language
    2. Macro
    3. Main function
    4. Memory
    5. Method
  12. O
    1. Object
    2. Optimization
  13. P
    1. Parameter
    2. Placeholder
    3. Pointer
    4. Precompiler
    5. Precompiler directive
    6. Prototype
    7. Python console
    8. Python format
    9. Python function
    10. Python import
    11. Python list
    12. Python main program
    13. Python variable
    14. Python-for
    15. Pääfunktio
    16. printf
  14. R
    1. Resource
    2. Return value
  15. S
    1. Statement
    2. Static typing
    3. String
    4. Syntax
  16. T
    1. Terminal
    2. Type
    3. Typecast
  17. U
    1. Unsigned
  18. V
    1. Value
  19. W
    1. Warning
    2. while
Completed: / exercises

Input / Output

Learning goals: Programmatic usage of I/O pins for different use cases in an embedded device
Input / Output, or also known as I/O means transfering information between the components of a computer and its peripherals. Inputs are the inputs / signals / data received by the component, like a button press, or a message from a peripheral device. Outputs are signals or information sent by the component, like a control command to a peripheral device.
Usually, physical components and the logic required to control them through I/O are integrated to the microcontroller or its board. Below is a list of typical components, some of which we are going to use in this course.
Peripheral devices are either digital or analog. Digital components are often more complex, they have different buses, and bit values (eg. pre-defined voltage levels) are used to communicate with them.
Analog components output different voltage levels, that can be anything between ground and operating voltage (for example 0-3.3V). As an example, many simple sensors output their measurement result as an analog signal. For a computer, these signals need to be first converted into digital form or more simply put, into numerical values, after which they can be handled numerically. Specifically for this task, there are analog-to-digital converters integrated into microcontrollers, that produce (rounded) numerical values in pre-defined resolution from input voltage. The resolution can be for example 8-bit, in which case the range would be values 0-255. In the case of the Pico, the resolution is 12 bits, so we can have from 0 to 4095 values.
Now, the task of the programmer is to convert the value given by AD-converter into a value that corresponds with a measurable quantity of the physical world, after which it can be handled in the program.
Examples of this kind of sensors are different temperature / air pressure / light sensors and also a microphone. If we assume the measurement range of a temperature sensor to be 0-100C, the programmer would have to create a conversion function that converts the values from AD-converters value (e.g. 0-255) to temperature (0-100C). After that, we could tell the user that the temperature of the room is for example +21C by using the screen of the device.
The sensors integrated to the extension board (HAT) of Pico are mainly digital, so we are not going to cover the use of the ADC in the basic material.

Pin

Okay, let's look at the basic stuff first. A pin means a physical leg or connector of a microchip / a component. The purpose of pins / leads is to connect the component to the board both electronically and mechanically. Each of the pin of a circuit have a certain use. Pin layout visualizes, what or which are the uses of each pin. As we can see, sometimes one pin can have multiple uses, depending on the functionalities of the device. This way, the functions of a device are restricted so that we can only use some of its functionalities at the same time.
Below as an example is the pin layout for Intel 4004, the world's first commercial microprocessor from 1971.
"Intel 4004, world

Pins and bits

And again some revision from the Bitwise operations-lecture material. We should keep in mind the common principle that in program code, each of the peripheral device's, or now also microcontroller's pin corresponds to one bit. For the handling of these bits, we have the bitwise operations of C.
Pins are given a logical name to make the job of a programmer (and an electronics designer) easier, for example SWCLK, , RUN (for reset) or GPIO16 for the GPIO General use pin 16. These names correspond with the names in peripheral device libraries most of the time, so that there exists a constant which is used to perform the bitwise operations required.
An example. We reset a device by zeroing bit RUN from the control register of a device. (Usually, resetting a device programmatically is not this straightforward, but we got and exiting example at least...)
   control_register = control_register & ~(1 << RUN); //Clears the run bit in the register
Some of the pins are reserved for general use (General Purpose I/O, GPIO) and the use case of these pins can be freely defined by the programmer, of course taking into account the peripheral devices that are to be connected to these pins. Logically, in microcontrollers, GPIO-pins are sometimes grouped into I/O-ports, so that 8 pins are logically thought of as one port. This is useful if a device needs numerous I/O-buses, as they can be logically handled as one unit and controlling them is easy with binary values. However, Pico thinks of all its I/O-ports separately, if the programmer does not excplicitly define the logical ports for desired pins. This is not needed in the course project.
The following figures show the pinout of the RP2040 chip (the microcontroller inside the Raspberry Pi Pico) and the pinout of the Raspberry Pi Pico board itself.
RP2040 pinout
Raspberry Pi Pico Pinout
Earlier we mentioned that some pins have dedicated purposes, while others can be used for general input/output (I/O) to connect external devices. The RP2040 is a bit more flexible: it does not assign a fixed pin to every peripheral (see all peripherals in the |architecture diagram). Instead, many pins can be configured for different functions.
This explains why, in the Raspberry Pi Pico pinout, you see that most pins list multiple possible functions. But how can a single pin serve different roles? The answer is that in the RP2040 (and also the RP2350) the chip allows us to “redirect” or connect a peripheral to one of several possible pins. In other words, we can decide which role a pin takes at a given time.
For example, suppose we want to use UART. (We will study UART later in the course, but for now just remember that it provides two-way serial communication between devices, using two lines: one for transmit and one for receive.) On the Pico, you can map UART to different pin pairs: such as pins 4 and 5, or pins 8 and 9, or pins 20 and 21.

Memory-mapped I/O

The meaning of memory-mapped I/O was that we reserve memory positions from the main memory of the device to function as (device)registers, that are connected to the pins of a peripheral device. We can control the bits of these memory positions via variables, which allows us to interact with the device from our program. These memory positions can be thought to form the data, address and control buses, in such a capacity in which they are needed by the device:
Before looking at the different types of registers, it is important to clear up a possible misunderstanding. When we say that peripherals are memory-mapped, this does not mean that the peripherals are given RAM to store data. What we mean is that the peripherals are placed in the CPU’s addressable memory space. In practice, this allows the CPU to read and write to them using the same instructions it uses for RAM access. Behind the scenes, the system bus and address decoder make sure that each memory address is directed to the correct hardware: either actual RAM, Flash, or a peripheral. For peripherals, the registers is not using system RAM, but small hardware elements such as flip-flops or latches that hold configuration bits or reflect the current hardware state.
"Address mapping for 2040. Peripherals and GPIO use different memory areas than RAM"
After this incise, let's go back to the type of registers. So, there are three types of registers: address, control and data registers. Peripheral device can provide many registers that fall into one of these categories, whichever combination of these three types is possible, depending on the implementation of the device itself. In Pico, to control some very complex peripheral device, we might need tens of registers. For this reason, it is indeed very relieving to use ready-made libraries to play with these devices!
We need to know the following things about all of these registers:
As an example, let’s look at one register layout from the Raspberry Pi RP2040. This register belongs to the on-chip voltage regulator, which generates the DVDD supply used by the chip’s digital logic.
"Digital Voltage regulator register layout"
DVDD powers the processor core and other digital blocks inside the RP2040, and it normally runs at about 1.1V. This is much lower than the 3.3V used by the chip’s I/O pins, because the digital logic does not need as high a voltage. The on-chip regulator allows DVDD to be generated internally from IOVDD (the 3.3V I/O supply) or from another supply between 1.8V and 3.3V. From the diagram we can see that the size of the register is 32 bits (31-0). Several bits are reserved, but some fields contain useful information:
If we want to change the DVDD voltage, we would write to the VSEL field of this memory-mapped register. To enable or disable the regulator, we would modify the HIZ bit. Just like with other peripherals, this is done by reading and writing the register at its assigned address.
Let's supposse that we want to modify the voltage to 1.15 (that is, writing 1100 in VSEL). The Pico SDK provides the hw_write_masked helper function to safely update only the relevant bits of a register:
hw_write_masked(
(io_rw_32 *)(VREG_AND_CHIP_RESET_BASE + VREG_AND_CHIP_RESET_VREG_OFFSET), // address of VREG
(VREG_AND_CHIP_RESET_VREG_VSEL_1_15 << VREG_AND_CHIP_RESET_VREG_VSEL_LSB), // value 1100 shifted into place -> 4 positions
VREG_AND_CHIP_RESET_VREG_VSEL_BITS // mask for bits [7:4]
);
In this example, the base address VREG_AND_CHIP_RESET_BASE plus the offset VREG_AND_CHIP_RESET_VREG_OFFSET gives the exact address of the VREG register. The symbolic constant VREG_AND_CHIP_RESET_VREG_VSEL_1_15 corresponds to the binary value 1100, which selects a core voltage of 1.15 V. The macro VREG_AND_CHIP_RESET_VREG_VSEL_LSB is 4, meaning that the VSEL field starts at bit 4, so the value must be shifted into the correct position. Finally, VREG_AND_CHIP_RESET_VREG_VSEL_BITS provides the write mask that ensures only bits [7:4] are modified, leaving all other register bits untouched.
But do not worry if it looks very complicated. Actually, it is!!! you usually do not need to go that deeper and the SDK API would offer much easier methods, without the need to have to check all the register values. In our case: 
#include "hardware/vreg.h

int main(void){
    vreg_set_voltage(VREG_VOLTAGE_1_1_15) //set DVDD to 1.15 V
}
This is not that difficult, is it?

Datasheet

The manual or datasheet of a component or a microcontroller explains in great detail every internal functionality and integrated circuit of the device. Datasheet functions as reference when programming with the hardware.
A datasheet is most of the time English-language, strongly based on professional vocabulary and hundreds or thousands of pages long, when talking about more complex devices. Just the datasheet of a normal, 8-bit Arduino microcontroller is just about 300 pages long! So when thinking about how simple controlling a pin is with Arduino, it is surprising to know that behind those operations are tens of pages of material in the datasheet, most of which the programmer does not need to know anything about. The datasheets of more complex devices are, almost without exception, even more broad. For example, the datasheet of the microcontoller in our Pico, RP2040, is 644 pages long!
Fortunately, instead of browsing through hundreds of pages of datasheets, ready-made libraries, functions, macros and constants are available for development environments, where the management of peripheral devices is already implemented and ready for higher-level functionalities.

A peek into Pico

In the image below, you can see a block diagram of the functionalities of Pico's microcontroller (RP2040). As we can see, Pico is pretty sophisticated device with plenty of functionalities. Two ARM Cortex-M0+ cores are integrated into it, along with 264 kilobytes of SRAM memory for program execution. The microcontroller manages many peripheral devices, for example two UART serial communications circuits, clock circuit and two I2C-buses. These will be discussed in greater detail in later materials.
"RP2040 MCU"
Below is the pin layout of Pico W. Pins are given a logical name, for example VSYS or GPIO16 to make the job of a programmer (and an electronics designer) a little bit easier.
Most of the pins are assigned for general purpose (General Purpose I/O, GPIO) and the use cases of these pins are up to the programmer to decide, of course considering the peripheral devices connected to these pins. In Pico, some of the GPIO pins are also assigned special purposes at the time of designing the device, and by using these pins, we could initialize a serial communications circuit and receive or send I2C-data.
"Pico W pinout"
In Pico, the libraries provided with the microcontroller give us ready-made functions to programmatically use the pins and peripheral devices connected to them. Below is and example of Pico SDK's function calls in gpio.h header file:
void gpio_init(uint gpio); //Prepare a GPIO for use
...
void gpio_deinit(uint gpio); //Release resources. No more in use
...
static inline bool gpio_get(uint gpio) { //Get the value of the pin.
    ...
}

Using I/O pins

Next, we will dive into the usage of I/O-pins in Pico with the help of a code example. The constants for the extension board of Pico are available in the pins.h header file added into our project.
Our example below, in all its beauty, uses the button of the extension board hat as an on/off-switch for the LED. So, here we need to define two pins for the use of our program: the pin corresponding to the button and the pin for LED.
We will use the gpio-library provided by Pico SDK. Because some known I/O-pins are connected in the extension board to the button and the LED, we can include them in the program with a header file pins.h. To include a button in the program, we need to do these three things:
  1. Initialize the pins that control the button and the LED
    • This happens with the function gpio_init() from the gpio-library
  2. Create an interruption handler for the button press
    • Below is an interruption handler function buttonFxn
    • We will cover interruptions in more detail in near future. So will easy to understand.
  3. and of course, in the main-function we enable the pin corresponding to the button with the help of a library function
    • An interruption handler is assigned with the function gpio_set_irq_enabled_with_callback from the gpio-library
So, every time a button is pressed, this example program runs the function buttonFxn, where the pin corresponding to the LED changes its state, and which this way drives the LED of the extension board on / off. The example is explored in detail below.
#include <FreeRTOS.h>
#include <pico/stdlib.h>
#include <task.h>
#include <stdio.h>
#include <inttypes.h>
#include <pins.h>

// Interruption handler function for button press
void buttonFxn(uint gpio, uint32_t eventMask) {
    // We change the state of the LED using negation
    uint8_t pinValue = gpio_get(LED1);
    pinValue = !pinValue;
    gpio_put(LED1, pinValue);
}

int main(void) {

    stdio_init_all();

    // Initializing pins
    gpio_init(BUTTON1);
    gpio_set_dir(BUTTON1, GPIO_IN);
    
    gpio_init(LED1);
    gpio_set_dir(LED1, GPIO_OUT);

   // We set the buttonFxn as an interruption handler
   // for the button pin
   gpio_set_irq_enabled_with_callback(BUTTON1, GPIO_IRQ_EDGE_RISE, true, buttonFxn);

    vTaskStartScheduler();

    return 0;
}
Let's review this example step by step

SDK constants for the use of pins

Like mentioned before, the SDK of Pico's extension board provides us with a bunch of constants in the pins.h-header file. By using these constants we can use the different peripheral devices of the extension board. In this case, we are using the constants BUTTON1 and LED1 from the library.

Pin initialization

Next, we will initialize the pins we are going to use as inputs or outputs. The gpio-library of Pico SDK provides the constants and functions to perform this task. The constant GPIO_IN tells to the library function gpio_set_dir that we want to set a pin as an input. With the constant GPIO_OUT, we could set a pin as an output.
   gpio_init(BUTTON1);
   gpio_set_dir(BUTTON1, GPIO_IN);
    
   gpio_init(LED1);
   gpio_set_dir(LED1, GPIO_OUT);
Here, we will begin by initializing a pin with a constant from the library pins.h, so that we can tell Pico, which pins do we want to use in the program. When the initialization is done, we tell Pico, in which way we want to use the pins we just initialized. Here we set the pin as input or output with the library function gpio_set_dir. This function takes in as arguments the pin we want to set as input/output, and a constant, that defines the direction for that specific pin.

Pin interruption handler

For pins set as inputs, we (generally) need a handler function, which defines the actions that are performed when the button is pressed, and an interruption is caused. For this, we have the handler function buttonFxn in our program.
void buttonFxn(uint gpio, uint32_t eventMask) {
    // We change the state of the LED using negation
    uint8_t pinValue = gpio_get(LED1);
    pinValue = !pinValue;
    gpio_put(LED1, pinValue);
}
The function works in a following way: Firstly, we read the state of the LED-pin (on "1" / off "0") with the function gpio_get, and save the result to variable pinValue. This commonly used function needs as an argument the pin we want to read, in this case LED1. After this, the value is negated, which in practice means that we change the state of the LED to be on / off. The new state is then set as the current state of the LED with the function gpio_put.

Including the interruption to our program

Then we will go back to the function main. The initialized pins are now included in the program, but we need to assign another one of them an interruption handler, so that we can react to the button press in our program.
   // Setting interruption handler for button
   gpio_set_irq_enabled_with_callback(BUTTON1, GPIO_IRQ_EDGE_RISE, true, buttonFxn);
RTOS handles the tasks and interruption handler functions in a similar way. More about interruptions later, but when the state of the button changes (on falling edge, because of the constant GPIO_IRQ_EDGE_FALL), it causes an interruption. With the function gpio_set_irq_enabled_with_callback we set a function to be executed in response to the interruption, in other words, its handler. In this program, the function buttonFxn is the handler of this interruption.
We can also see that in addition to the constant and handler function, we give other arguments to the function from gpio-library. At first, we need to tell the library, what pin is this interruption handler associated with, here we obviously set the pin to be BUTTON1, that means the button that was initialized earlier. The second-to-last value true given to the function means that we want to enable the interruption now.
Note! We could have implemented the same checking of the button state with superloop-structure so that in an infinite loop we would ask the state of the button in every iteration, and if it was changed, we would perform some action. Well, these superloop-things again, but as we can see the same goal was achieved much easier by using a handler.

Outputting analog data: PWM

In microcontrollers, digital pins can only output two values: 0 (low, 0 V) or 1 (high, typically 3.3 V in the Pico). But what if we want to dim an LED, drive a motor or create something that looks like an “analog” signal? For this we can use Pulse Width Modulation (PWM). PWM is a technique where the pin is rapidly switched on and off, and the ratio of on-time to the total period (the duty cycle) represents the average output value.
We said before that each GPIO pin on the Pico can be configured to use one of these hardware functions, such as UART, SPI, or PWM. In Raspberry Pi Pico we use the gpio_set_function to that purpose. Hence, to use PWM on a pin, we first need to configure that pin’s function with gpio_set_function.
Inside the RP2040, the PWM hardware is organized into slices. There are eight slices in total, and each slice contains two channels (A and B). You can think of a slice as the basic PWM engine, and the channels as its outputs. Each GPIO pin that supports PWM is connected to one of these slice channels. This means that every pin capable of PWM is already “wired” internally to a particular slice. To use PWM correctly, we need to know which slice a pin belongs to. We can find this information in the RP2040 datasheet, but in practice it is much easier to use the SDK helper function pwm_gpio_to_slice_num, which returns the slice number for a given GPIO pin. Once the slice is identified, we enable it and set the duty cycle for our pin. If we do not explicitly configure anything else, the PWM counter runs with a default range of 0 to 65535. This is why the duty cycle values in the SDK are also given in the range 0–65535: a value of 0 means always off, 65535 means always on, and 32768 would be about 50% on-time.
Let’s look at a simple example where we control the brightness of a single LED connected to GPIO pin LED1 by controlling the duty cycle of PWM signal. 
// Configure GPIO pin for PWM
gpio_set_function(LED1, GPIO_FUNC_PWM);

// Find which PWM slice controls this pin
uint slice_num = pwm_gpio_to_slice_num(LED1);


// Set duty cycle (0-65535). Higher value = brighter LED.
pwm_set_gpio_level(LED1, 32768); // ~50% duty cycle

// Enable the PWM slice
pwm_set_enabled(slice_num, true);
In the previous code:

To conclude

In addition to memory-mapped I/O, another way of doing I/O exists: port-mapped I/O, where registers are used through separate in- and out-commands. Well, Pico does not use this kind of mechanism.
But hey.. based on the material, you can already create an embedded program, that blinks the LED of the device, if it recognizes a button press from its user! Time to celebrate?
?
Abstraction is a process through which raw machine language instructions are "hidden" underneath the statements of a higher level programming language. Abstraction level determines how extensive the hiding is - the higher the abstraction level, the more difficult it is to exactly say how a complex statement will be turned into machine language instructions. For instance, the abstraction level of Python is much higher than that of C (in fact, Python has been made with C).
Alias is a directive for the precompiler that substitus a string with another string whenever encountered. In it's basic form it's comparable to the replace operation in a text editor. Aliases are define with the #define directeve, e.g. #define PI 3.1416
Argument is the name for values that are given to functions when they are called. Arguments are stored into parameters when inside the function, although in C both sides are often called just arguments. For example in printf("%c", character); there are two arguments: "%c" format template and the contents of the character variable.
Array is a common structure in programming languages that contains multiple values of (usually) the same type. Arrays in C are static - their size must be defined when they are introduced and it cannot change. C arrays can only contain values of one type (also defined when introduced).
Binary code file is a file that contains machine language instructions in binary format. They are meant to be read only by machines. Typically if you attempt to open a binary file in a text editor, you'll see just a mess of random characters as the editor is attempting to decode the bits into characters. Most editors will also warn that the file is binary.
Binary number is a number made of bits, i.e. digits 0 and 1. This makes it a base 2 number system.
A bit is the smallest unit of information. It can have exactly two values: 0 and 1. Inside the computer everything happens with bits. Typically the memory contains bitstrings that are made of multiple bits.
Bitwise negation is an operation where each bit of a binary number is negated so that zeros become ones and vice versa. The operator is ~.
Bitwise operations are a class of operations with the common feature that they manipulate individual bits. For example bitwise negation reverses each bit. Some operations take place between two binary values so that bits in the same position affect each other. These operations include and (&), or (|) and xor (^). There's also shift operations (<< and >>) where the bits of one binary number are shifted to the left or right N steps.
Byte is the size of one memory slot - typically 8 bits. It is the smallest unit of information that can be addressed from the computer's memory. The sizes of variable types are defined as bytes.
External code in C is placed in libraries from which they can be taken to use with the #include directive. C has its own standard libraries, and other libraries can also be included. However any non-standard libraries must be declared to the compiler. Typically a library is made of its source code file (.c) and header file (.h) which includes function prototypes etc.
Functions in C are more static than their Python counterparts. A function in C can only have ne return value and its type must be predefined. Likewise the types of all parameers must be defined. When a function is called, the values of arguments are copied into memory reserved for the function parameters. Therefore functions always handle values that are separate from the values handled by the coe that called them.
C variables are statically typed, which means their type is defined as the variable is introduced. In addition, C variables are tied to their memory area. The type of a variable cannot be changed.
Character is a single character, referred in C as char. It can be interpreted as an ASCII character but can also be used as an integer as it is the smallest integer that can be stored in memory. It's exactly 1 byte. A character is marked with single quotes, e.g. 'c'.
Code block is a group of code lines that are in the same context. For instance, in a conditional structure each condtion contains its own code block. Likewise the contents of a function are in their own code block. Code blocks can contain other code blocks. Python uses indentation to separate code blocks from each other. C uses curly braces to mark the beginning and end of a code block.
Comments are text in code files that are not part of the program. Each language has its own way of marking comments. Python uses the # character, C the more standard //. In C it's also possible to mark multiple lines as comments by placing them between /* and */.
A compiler is a program that transforms C source code into a binary file containing machine language instructions that can be executed by the computer's processor. The compiler also examines the source code and informs the user about any errors or potential issues in the code (warnings). The compiler's behavior can be altered with numerous flags.
Complement is a way to represent negative numbers, used typically in computers. The sign of a number is changed by flipping all its bits. In two's complement which is used in this course, 1 is added to the result after flipping.
Conditional statement is (usually) a line of code that defined a single condition, followed by a code block delimited by curly braces that is entered if the condition evaluates as true. Conditional statements are if statements that can also be present with the else keyword as else if. A set of conditional statements linked together by else keywords are called conditional structures.
Conditional structure is a control structure consisting of one or more conditional statements. Most contrl structures contain at least two branches: if and else. Between these two there can also be any number of else if statements. It is however also possible to have just a single if statement. Each branch in a conditional structure cotains executable code enclosed within a block. Only one branch of the structure is ever entered - with overlapping conditions the first one that matches is selected.
Control structures are code structures that somehow alter the program's control flow. Conditional structures and loops belong to this category. Exception handling can also be considered as a form of control structure.
Data structure is a comman name for collection that contain multiple values. In Python these include lists, tuples and dictionaries. In C the most common data structures are arrays and structs.
Python's way of treating variable values is called dynamic typing aka duck typing. The latter comes from the saying "if it swims like a duck, walks like a duck and quacks like a duck, it is a duck". In other words, the validity of a value is determined by its properties in a case-by-case fashion rather than its type.
An error message is given by the computer when something goes wrong while running or compiling a program. Typically it contains information about the problem that was encountered and its location in the source code.
An exception is what happens when a program encounters an error. Exceptions have type (e.g. TypeError) that can be used in exception handling within the program, and also as information when debugging. Typically exceptions also include textual description of the problem.
Flags are used when executing programs from the command line interface. Flags are options that define how the program behaves. Usually a flag is a single character prefixed with a single dash (e.g. -o) or a word (or multiple words connected with dashes) prefixed with two dashes (e.g. --system. Some flags are Boolean flags which means they are either on (if present) or off (if not present). Other flags take a parameter which is typically put after the flag separated either by a space or = character (e.g. -o hemulen.exe.
Floating point numbers are an approximation of decimal numbers that are used by computers. Due to their archicture computers aren't able to process real decimal numbers, so they use floats instead. Sometimes the imprecision of floats can cause rounding errors - this is good to keep in mind. In C there are two kinds of floating point numbers: float and double, where the latter has twice the number of bits.
Header files use the .h extension, and they contain the headers (function prototypes, type definitions etc.) for a .c file with the same name.
Headers in C are used to indicate what is in the code file. This includes things like function prototypes. Other typical content for headers are definition of types (structs etc.) and constants. Headers can be at the beginning of the code file, but more often - especially for libraries - they are in placed in a separate header (.h) file.
Hexadecimal numbers are base 16 numbers that are used particularly to represent memory addresses and the binary contents of memory. A hexadecimal number is typically prefixed with 0x. They use the letters A-F to represent digits 10 to 15. Hexadecimals are used because each digit represents exactly 4 bits which makes transformation to binary and back easy.
In Python objects were categorized into mutable and immutable values. An immutable value cannot have its contents changed - any operations that seemingly alter the object actually create an altered copy in a new memory location. For instance strings are immutable in Python. In C this categorization is not needed because the relationship of variables and memory is tighter - the same variable addresses the same area of memory for the duration of its existence.
When a variable is given its initial value in code, the process is called initialization. A typical example is the initialization of a number to zero. Initialization can be done alongside with introduction: int counter = 0; or separately. If a variable has not been initialized, its content is whatever was left there by the previous owner of the memory area.
Instruction set defines what instructions the processor is capable of. These instructions form the machine language of the processor architecture.
Integers themselves are probably familiar at this point. However in C there's many kinds of integers. Integer types are distinguished by their size in bits and whether they are signed or not. As a given number of bits can represent up to (2 ^ n) different integers, the maximum value for a signed integer is (2 * (n - 1))
Python interpreter is a program that transforms Python code into machine language instructions at runtime.
The moment a variable's existence is announed for the first is called introduction. When introduced, a variable's type and name must be defined, e.g. int number;. When a variable is introduced, memory is reserved for it even though nothing is written there yet - whatever was in the memory previously is still there. For this reason it's often a good idea to initialize variables when introducing them.
Iteroitava objekti on sellainen, jonka voi antaa silmukalle läpikäytäväksi (Pythonissa for-silmukalle). Tähän joukkoon kuuluvat yleisimpinä listat, merkkijonot ja generaattorit. C:ssä ei ole silmukkaa, joka vastaisi Pythonin for-silmukan toimintaa, joten taulukoiden yms. läpikäynti tehdään indeksiä kasvattavilla silmukoilla.
Keywords are words in programming languages that have been reserved. Good text editors generally use a different formatting for keywords (e.g. bold). Usually keywords are protected and their names cannot be used for variables. Typical keywords include if and else that are used in control structures. In a way keywords are part of the programming language's grammar.
A library is typically a toolbox of functions around a single purpose. Libraries are taken to use with the include directive. If a library is not part of the C standard library, its use must also be told to the compiler.
Logical operation refers to Boole's algebra, dealing with truth values. Typical logical operations are not, and, or which are often used in conditional statements. C also uses bitwise logical operations that work in the same way but affect each bit separately.
Machine language is made of instructions understood by the processor. Machine language is often called Assembly and it is the lowest level where it's reasonable for humans to give instructions to computers. Machine language is used at the latter part of this course - students taking the introduction part do not need to learn it.
Macro is an alias that defines a certain keyword to be replaced by a piece of code. When used well, macros can create more readable code. However, often the opposite is true. Using macros is not recommended in this course, you should just be able to recognize one when you see it.
In C the main function is the starting point when the program is run. The command line arguments of the program are passed on to the main function (although they do not have to be received), and its return value type is int. At its shortest a main function can defined as int main().
When programs are run, all their data is stored in the computer's memory. The memory consists of memory slots with an address and contents. All slots are of equal size - if an instance of data is larger, a continuous area of multiple memory slots is reserved.
Method is a function that belongs to an object, often used by the object to manipulate itself. When calling a method, the object is put before the method: values.sort().
Object is common terminology in Python. Everything in Python is treated as objects - this means that everything can be referenced by a variable (e.g. you can use a variable to refer to a function). Objects are typically used in object-oriented languages. C is not one.
Optimization means improving the performance of code, typically by reducing the time it takes to run the code or its memory usage. The most important thing to understand about opimization is that it should not be done unless it's needed. Optimization should only be considered once the code is running too slowly or doesn't fit into memory. Optimization should also not be done blindly. It's important to profile the code and only optimize the parts that are most wasteful.
A parameter is a variable defined alongside with a function. Parameters receive the values of the function's arguments when it's called. This differentation between parameters and arguments is not always used, sometimes both ends of the value transfer are called arguments.
Placeholders are used in string formatting to mark a place where a value from e.g. a variable will be placed. In Python we used curly braces to mark formatting placeholders. In C the % character is used which is followed by definitions, where the type of the value is mandatory. For instance "%c" can only receive a char type variable.
Pointers in C are special variables. A pointer contains a memory address of the memory location where the actual data value is located. In a sense they work like Python variables. A variable can be defined as a pointer by postfixing its type with * when it's being introduced, e.g. int* value_ptr; creates a pointer to an integer. The contents of the memory address can be fetched by prefixing the variable name with * (e.g. *value_ptr. On the other hand, the address of a memory adress can be fetched by prefixing a variable name with &, (e.g. &value.
The C precompiler is an apparatus that goes through all the precompiler directives in the code before the program is actually compiled. These directives include statements which add the source code of the included libraries into the program, and define directives that can define constant values (aliases) and macros.
Directives are instructions that are addressed at the precompiler. They are executed and removed from the code before the actual compilation. Directives start with the # character. The most common one is include which takes a library into use. Another common one is define, which is used e.g. to create constant values.
Prototype defines a function's signature - the type of its return value, its name and all the arguments. A prototype is separate from the actual function definition. It's just a promise that the function that matches the prototype will be found in the code file. Prototypes are introduced at the beginning of the file or in a separate header file. In common cases the prototype definition is the same as the line that actually starts the function introduction.
Interactive interpreter or Python console is a program where users can write Python code lines. It's called interactive because each code line is executed after its been fully written, and the interpreter shows the return value (if any).
The format method of string in Python is a powerful way to include variable values into printable text. The string can use placeholders to indicate where the format method's arguments are placed.
Python functions can have optional parameters that have a given default value. In Python the values of arguments in a function call are transferred to function parameters through reference, which means that the values are the same even though they may have different names. Python functions can have multiple return values.
In Python the import statement is used for bringing in modules/libraries - either built-in ones, thrid party modules or other parts of the same application. In Python the names from the imported module's namespace are accessible through the module name (e.g. math.sin). In C libraries are taken to use with include, and unlike Python import it brings the library's namespace into the program's global namespace.
Python lists were discovered to be extremely effective tools in Elementary Programming. A Python list is an ordered collection of values. Its size is dynamic (i.e. can be changed during execution) and it can include any values - even mixed types. Lists can also include other lists etc.
In Python main program is the part of code that is executed when the program is started. Usually the main program is at the end of the code file and most of the time under if __name__ == "__main__": if statement. In C there is no main program as such, code execution starts with the main function instead.
In Python a variable is a reference to a value, a connection between the variable's name in code and the actual data in memory. In Python variables have no type but their values do. The validity of a value is tested case by case when code is executed. In these ways they are different from C variables, and in truth Python variables are closer to C pointers.
Pythonin for-silmukka vastaa toiminnaltaan useimmissa kielissä olevaa foreach-silmukkaa. Se käy läpi sekvenssin -esim. listan - jäsen kerrallaan, ottaen kulloinkin käsittelyssä olevan jäsenen talteen silmukkamuuttujaan. Silmukka loppuu, kun iteroitava sekvenssi päättyy.
Pääfunktio on C:ssä ohjelman aloituspiste ja se korvaa Pythonista tutun pääohjelman. Oletuksena pääfunktion nimi on main ja se määritellään yksinkertaisimmillaan int main().
Resource referes to the processing power, memory, peripheral devices etc. that are availlable in the device. It includes all the limitations within which programs can be executed and therefore defines what is possible with program code. On a desktop PC resources are - for a programmer student - almost limitless, but on embedded devices resources are much more scarce.
Return value is what a function returns when its execution ends. In C functions can only have one return value, while in Python there can be multiple. When reading code, return value can be understood as something that replaces the function call after the function has been executed.
A statement is a generic name for a single executable set of instructions - usually one line of code.
C uses static typing This means that the type of variables is defined as they are created, and values of different types cannot be assigned to them. The validity of a value is determined by its type (usually done by the compiler). Python on the other hand uses dynamic typing aka.duck typing.
In Python all text is handled as strings and it has no type for single characters. However in C there are no strings at all - there's only character arrays. A character array can be defined like a string however, e.g. char animal[7] = "donkey"; where the number is the size of the array + 1. The +1 is neede because the string must have space for the null terminator '\0' which is automatically added to the end of the "string".
Syntax is the grammar of a programming language. If a text file does not follow the syntax of code, it cannot be executed as code, or in the case of C, it cannot be compiled.
Terminal, command line interface, command line prompt etc. are different names to the text-based interface of the operating system. In Windows you can start the command line prompt by typing md to the Run... window (Win+R). Command line is used to give text-based commands to the operating system.
The data in a computer's memory is just bits, but variables have type. Type defines how the bits in memory should be interpreted. It also defines how many bits are required to store a value of the type. Types are for instance int, float and char.
Typecast is an operation where a variable is transformed to another type. In the elementary course this was primarily done with int and float functions. In C typecast is marked a bit differently: floating = (float) integer}. It's also noteworthy that the result must be stored in a variable that is the proper type. it is not possible to change the type of an existing variable.
Unsigned integer is a an integer type where all values are interpreted as positive. Since sign bit is not needed, unsigned integers can represent twice as large numbers as signed integers of the same size. An integer can be introduced as unsigned by using the unsigend keyword, e.g. unsigned int counter;.
In the elementary programming course we used the term value to refer to all kinds of values handled by programs be it variables, statement results or anything. In short, a value is data in the computer's memory that can be referenced by variables. In C the relationship between a variable and its value is tighter as variables are strictly tied to the memory area where its value is stored.
A warning is a notification that while executing or - in this course particularly - compiling it, something suspicious was encountered. The program may still work, but parts of it may exhibit incorrect behavior. In general all warnings should be fixed to make the program stable.
One way to print stuff in C is the printf function, which closely resembles Python's print function. It is given a printable string along with values that will be formatted into the string if placeholders are used. Unlike Python, C's printf doesn't automatically add a newline at the end. Therefore adding \n at the end is usually needed.
Out of loops, while is based on repetition through checking a condition - the code block inside the loop is repeated until the loop's condition is false. The condition is defined similarly to conditional statements, e.g. while (sum < 21).