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

Interrupts

Learning objectives: Interrupts and their use in embedded devices.
In a computer, an interrupt is an internal or external signal sent to the processor that, as the name suggests, interrupts the processor's ongoing task. When an interrupt occurs, the processor saves its state (program execution state, registers, etc.) and switches to the execution of the interrupt handler. Once the handler finishes, the processor restores its saved state and continues executing the program exactly from where it left off.
The image below shows the pin configuration of the ATmel ATtiny2313 microcontroller, with two external hardware interrupt pins (INT0 and INT1) marked in red. These pins can be connected to the interrupt line from a peripheral device, allowing it to capture the interrupt signals sent by the device. In general, microcontrollers have dedicated pins for external interrupts, physically connected to the interrupt management logic of the chip. The data sheets of peripherals/components define exactly what types of interrupts they can generate.
"External interrupt pins"
Interrupts come in two types. An interrupt can be hardware-based (either internal to the CPU or from a peripheral) and is typically caused by an asynchronous event (independent of the program's timing) inside the CPU or a peripheral. Thus, from the program's perspective, a hardware interrupt can occur at any moment. Hardware interrupts can be triggered by events inside the CPU, such as a divide by zero error (an error condition), or externally, for example, when a peripheral device signals that it needs attention because new data is available or an error occurred.
Software interrupts are triggered by a special machine language interrupt instruction, such as the INT instruction on Intel x86 processors. A software interrupt signals the CPU, and the operating system/firmware handles it the same way as hardware interrupts, executing the corresponding handler function.
Interrupts have a priority. Higher-priority interrupts are handled first. Priority becomes important when multiple interrupts occur simultaneously or while a lower-priority interrupt handler is executing. In such cases, a higher-priority interrupt will preempt the lower-priority handler and execute first.
In embedded systems, the RESET pin hardware interrupt has the highest priority. Next are hardware interrupts, which are typically time-critical, followed by software interrupts, for which the programmer can set the desired priority. Software interrupts are therefore controlled according to how the programmer defines them (and they can also preempt each other).
An interrupt handler (handler) is almost like a function, but it is never called from the running program. This is important because before executing the interrupt handler, the processor state must be saved, and calling the handler as a function would not perform this save. The handler also does not return any values, but it can use global variables or registers to pass information. In C, however, the handler is implemented as a function, and the RTOS must be informed that this function is now an interrupt handler.
Handlers are time-critical for two reasons: they interrupt the running program, and they can preempt each other. This means that it is easy (incorrectly) to block the entire program's execution with a high-priority handler that takes too long to execute. Now, TI-RTOS specifies that a hardware interrupt should last a maximum of 5 microseconds and a software interrupt should last around 100 microseconds. Therefore, only minimal code can be executed in the handler. For this reason, handlers often only modify the values of registers or global state variables. A good practice, for example, is to use a state variable in the handler to indicate that the peripheral has new data, and then perform the actual read operation outside the handler in the main program. Again, these are priceless free tips. Well, more on this in the State Machines lecture materials.

SensorTag Interrupts

Next, we will go through different ways to use interrupts in RTOS with an example. We will demonstrate both external hardware interrupts (pin and peripheral). Internal hardware interrupt is described in the sarjaliikenne when we discuss about UART serial communication.

Pin Interrupt

In the previous chapter, we introduced an interrupt that responds to changes in pin state. Let’s revisit this topic...
... 
// Pin configuration
PIN_Config buttonConfig[] = {
   Board_BUTTON0  | PIN_INPUT_EN | PIN_PULLUP | PIN_IRQ_NEGEDGE,
   PIN_TERMINATE 
};
...
// Interrupt handler
void buttonFxn(PIN_Handle handle, PIN_Id pinId) {
   ...
}

Int main() {
   ...
   // Register the buttonFxn handler for the pin
   if (PIN_registerIntCb(buttonHandle, &buttonFxn) != 0) {
      System_abort("Error registering button callback function");
   }
   ...
}
We can see in the Pin_Config table that the pin is now set with the constant PIN_IRQ_NEGEDGE, which allows the pin to trigger an interrupt. In this case, the interrupt occurs when the pin’s state changes on the falling edge, meaning from HIGH (operating voltage) -> LOW (ground level). A pin interrupt can also be set to trigger on the rising edge when the state changes from LOW -> HIGH, using the constant PIN_IRQ_POSEDGE, or even on both edges with PIN_IRQ_BOTHEDGES.
We assign the interrupt handler function with the call PIN_registerIntCb, where we specify the buttonFxn function. The interrupt-specific functionality is then implemented in the function definition.

Peripheral Interrupts

As an example of an external interrupt from a peripheral in the SensorTag, we introduce the versatile MPU9250 sensor (42-page datasheet). This sensor integrates a gyroscope, accelerometer, and magnetometer. It can also be used as a compass.
The MPU9250 may work via interrupt by connecting its external interrupt line Board_MPU_INT (found in the CC2650STK.h header file) to the SensorTag. The interrupt is enabled in the same way as the pin interrupt described above.
In the following example, we will learn how to enable and disable external interrupts.
// RTOS variables for MPU9250 pins
static PIN_Handle MpuHandle;
static PIN_State MpuState;

// MPU9250 pin configuration
static PIN_Config MpuConfig[] = {
    Board_MPU_INT | PIN_INPUT_EN | PIN_PULLDOWN | PIN_IRQ_DIS | PIN_HYSTERESIS,
    PIN_TERMINATE
};

// Handler function
Void MpuFxn(PIN_Handle handle, PIN_Id pinId) {
      ...
}

Void sensorTask(UArg arg0, UArg arg1) {

   // Enable MPU9250 interrupt on the rising edge
   PIN_setInterrupt(MpuConfig, PIN_ID(Board_MPU_INT) | PIN_IRQ_POSEDGE); 
   ...
   // Disable MPU9250 interrupts
   PIN_setInterrupt(MpuConfig, PIN_ID(Board_MPU_INT) | PIN_IRQ_DIS);
}

int main(void) {
   ...
   // Enable MPU interrupt pin
   MpuHandle = PIN_open(&MpuState, MpuConfig);
   if (MpuHandle == NULL) {
      System_abort("Pin open failed!");
   }

   // Register the interrupt handler function
   PIN_registerIntCb(MpuHandle, &MpuFxn);
   ...
}
Let’s break down this example. In the main function, we activate the interrupt line in the program and assign the interrupt handler function MpuFxn.
In the pin configuration MpuConfig, there is a new constant PIN_IRQ_DIS (disable), which indicates that the pin-triggered interrupts are initially disabled. Therefore, when we want to receive interrupts (e.g., in a task), we use the PIN_setInterrupt function to enable the interrupts with the constant PIN_IRQ_POSEDGE. Typically, it's a good practice to enable interrupts at the latest possible moment in the code to prevent them from interfering with the program’s execution before they're actually needed.
In the example, the implementation of sensorTask also includes enabling the interrupt with the PIN_setInterrupt function. This way, we can programmatically enable and disable interrupts as needed.

Timers

The RTOS also provides a timer through the Clock library, which allows us to implement scheduled events, i.e., interrupts at specific intervals. For example, we could use a timer to read sensor data once per second, communicate with a peripheral, or blink an LED. In the previous state machine material, there was already an example of this, where we changed the state of the state machine once per second, which resulted in reading sensor data and printing the new measurements to the screen.
An example tells us more than a thousand words:
...
#include <ti/sysbios/knl/Clock.h>
...

// Clock interrupt handler
Void clkFxn(UArg arg0) {

   // Example style: don't do this, as it's very slow
   sprintf(str,"System time: %.5fs\n", (double)Clock_getTicks() / 100000.0);
   System_printf(str);
   System_flush();
}

int main(void) {

   ...
   Board_initGeneral();

   // RTOS clock variables
   Clock_Handle clkHandle;
   Clock_Params clkParams;

   // Initialize the clock
   Clock_Params_init(&clkParams);
   clkParams.period = 1000000 / Clock_tickPeriod;
   clkParams.startFlag = TRUE;

   // Enable the clock in the program
   clkHandle = Clock_create((Clock_FuncPtr)clkFxn, 1000000 / Clock_tickPeriod, &clkParams, NULL);
   if (clkHandle == NULL) {
      System_abort("Clock create failed");
   }
   ...
}
Once again, we use a configuration structure, in this case Clock_Params. In the period member, we set the desired time in clock cycles. Let's recall the previous material, where it was mentioned that one tick corresponds to about 10 microseconds in our time.
Now we set the period to 100000, which gives us a timer interrupt approximately once per second. The inaccuracy here comes from the fact that the clock in the Clock library is implemented in software, and thus its interrupts are software interrupts. When we run the example program, we can see that the time calculation fluctuates by a few tens of microseconds in either direction. Well, this level of accuracy is sufficient for us humans.
The startFlag member in the configuration structure can be used to start the clock immediately from the Clock_create call (startFlag=TRUE) or to start it later with the Clock_start call (startFlag=FALSE). The clock is stopped with the Clock_stop call. These calls require the clock handle as a parameter.
The Clock_create call introduces something new to us. The first parameter of the call is the interrupt handler, in this case, the clkFxn function. The purpose of this function is to demonstrate how a software-implemented clock works. It's important to remember that printing to the console is a very slow operation (from the MCU's perspective), so in this example, we are clearly violating the rule that an interrupt handler's execution time should not be too long. Well, we'll forgive it this time, as we wanted to measure the inaccuracy of the software interrupt. (A better way to achieve the same result would be to store the clock time in a global variable and print it to the console in a task using the state variable.)
The second parameter of the Clock_create call, timeout (in this case, 1 second), tells the timer how many ticks it should wait before the first interrupt event. The idea here is that we can also implement one-time (one-shot) timers. In these clocks, the period member of the Clock_params structure is set to zero, and the desired time delay is passed to the timeout argument.
The figure shows two different types of clocks in the Clock library.
"Two types of clocks in RTOS"
The library allows us to create multiple simultaneous clocks in our program. We only need to define a handle for each clock, set the parameters, and create the clocks using the Clock_create call. However, this is not particularly efficient; a better approach would be to implement a single clock interrupt and count multiple time delays at once.
Additionally, the library introduces us to the familiar Clock_tickPeriod variable, which tells us how many microseconds one tick represents. The Clock_getTicks call provides the elapsed time in ticks since the program started.

Real-time Clock

On top of all this, the RTOS also offers a library for a real-time clock called Seconds, which operates in human-readable time. The only drawback is that we need to manually initialize the clock by setting it to the correct time before using it.
Once again, let's rely on the power of an example:
#include <ti/sysbios/hal/Seconds.h>
...
Void clkFxn(UArg arg0) {

   time_t now = time(NULL);
   struct tm *timeinfo = localtime(&now);
   System_printf("The time is %02d:%02d:%02d\n", timeinfo->tm_hour+3, timeinfo->tm_min, timeinfo->tm_sec);
   System_flush();
}

Int main() {
   ...
   // Set the real-time clock start time
   Seconds_set(1475578882); // A more interesting argument..
   ...
   }
First, we notice the Seconds_set call in the main function, which sets the clock to the desired time. Now things get interesting (well... for some people, it surely does!).
Here, the time is provided in Unix time, which is the number of seconds that have passed since January 1, 1970, 00:00:00 UTC, represented as a 32-bit integer. There are several websites available online that calculate the elapsed seconds for you, such as the Epoch converter. The number 1475578882 used in the above example corresponds to the time October 4, 2016, 11:01:22 GMT.
In the clkFxn function, we encounter some new things as we use the time.h standard library. The library provides the time(NULL) function, which returns the current real-time as a 32-bit integer. In addition, the time library provides several functions that convert the seconds into a more readable format. In the above example, the localtime call fills in the struct tm structure, allowing us to extract the hours, minutes, and seconds separately.
In the example, we also have to set the time zone in a somewhat awkward way using tm_hour+3.

In Conclusion

The RTOS abstracts the use of interrupts to something as simple as writing a handler as a function. We don't even necessarily know whether the library is interrupt-based or just a regular program function. To clarify this, it's important to read the documentation of the specific library. Otherwise, we might unknowingly create too heavy a handler for an interrupt.
?
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).