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

Exceptions

Learning Objectives: Firmware and exceptions during program execution.

Firmware

Firmware, known in the PC world as BIOS (Basic Input Output System), connects the computer system's components into a functioning computer. It initializes and boots the computer by starting the command interpreter or operating system and provides low-level interfaces (e.g., protections) for accessing hardware resources for the operating system and applications. In the PC world, various BIOS (or more modernly UEFI) systems include user-visible system setup programs and hardware tests performed during boot.
Generally, to ensure hardware compatibility, firmware provides a standardized integration environment for components from different manufacturers, enabling computer systems to be built with parts from multiple sources. This idea was pivotal (originally developed by IBM) to the success of PC technology in the early days of personal computing.
The services of firmware/BIOS are accessed through two mechanisms:
  1. By software interrupts from machine code (e.g., trap instructions)
  2. Through system calls from program code, which are used as if they were ready-made subroutine libraries.
Example: Printing a character on the screen using a BIOS call and a software interrupt:
mov ah, 0x0e    # Register AH function = 0x0E (Display Character)
mov al, 0x56    # Register AL character to print
int 0x10        # Interrupt 0x10 (BIOS video service)
Firmware is often stored in read-only memory (ROM) as machine/microcode that the program code calls using jump instructions, much like regular subroutines. In early personal computers, firmware was implemented on a ROM chip integrated into the processor’s circuit board and visible as part of program memory. BIOS updates were done by physically replacing the chip.
Example: The Kernal functions in the Commodore 64’s firmware were implemented using machine code.

BIOS Call Layering

System calls often have a higher-level wrapper function that invokes the actual low-level BIOS system call. For instance, in the C programming language, the standard library (unistd.h) provides system calls for programs, which are then used by standard library implementations.
Since these calls are still from a lower/more hardware-adjacent layer, they require the programmer to consider more hardware/operating system-specific details. This kind of layering from the program through the operating system to the firmware is necessary because system calls have broader permissions for system resources (kernel mode) than the calling program (user mode). Firmware calls are therefore "hidden" from the programmer.
For example, in the x86 processor architecture, there are different protection rings. Additionally, some processors have protected instructions that only system calls can execute. Before executing the call, the firmware verifies the permissions.

Exceptions and their management

Exceptions

In general, an exception is an event that originates outside the program being executed, interrupts the program's control flow (engl. control flow), and requires the processor to handle it by executing an exception handler (engl. exception handler). After the handler is executed, the processor resumes the program from where it was interrupted.
The event may be related to the instruction being executed, such as attempting to divide by zero. External events can also interrupt the program execution, such as a message from an I/O device. Internally, the processor changes its state, for example, by setting status flags or modifying register values, which the operating system/program/firmware can read to determine what exception occurred.
Exception handling is thus a collaboration between hardware and software. The hardware sets the state change, and the software reacts to it. Generally, operating systems/firmware have default handlers for exceptions, but custom handlers can be written selectively for specific cases. Processors also support software-defined exceptions, which programmers can use freely.
In this way, exceptions provide a mechanism for collaboration between applications and the operating system. Applications can request lower-level services, such as I/O, from the operating system via exceptions. The operating system then manages this task in collaboration with the firmware. Similarly, peripherals communicate with applications via exceptions.
In systems supporting multitasking, exceptions are often used to control the concurrent execution of different program tasks. Examples include SensorTag’s RTOS libraries like Task, Pin, UART, etc.

Handling Exceptions

Exceptions are identified by their unique (positive, starting from 0) identifier number. This order is determined during the design phase of the processor hardware or during the BIOS initialization phase. The identifier number also indicates the priority order of the exceptions, with the smallest number representing the highest priority. Based on these numbers, an exception table is created, which stores the handler's memory address for each exception. Thus, handling an exception involves an (unconditional) jump to the memory address where the handler code is located. In some architectures (e.g., modern x86), a parameter can be passed to the handler, similar to subroutine calls.
For example, the x86 interrupt descriptor table. In embedded systems, this is called an interrupt vector table.
Often, the exception table itself is located at the very beginning of memory, starting at address 0. During system startup, the firmware and/or operating system initializes the exception table with default values. Operating systems can usually also create their exceptions towards the end of the exception table. Similarly, applications can modify the vector memory addresses within the limits of their permissions. In embedded systems, for instance, programmers typically have the freedom to modify the interrupt vector values while implementing handlers.
Each exception must have a handler , which can either be the operating system’s default handler or a custom handler written by the programmer. As presented earlier in the context of interrupts, a handler functions similarly to a subroutine, but with key differences under the hood:
  1. During an exception, in addition to general registers, the status register is also saved. Some processors have dedicated registers to store the exception context, such as the address of the instruction that caused the exception.
  2. If a stack is used, it is the operating system’s stack, not the program’s stack.
  3. Some processors have dedicated machine instructions for returning from exception handlers, separate from subroutine return instructions. In x86, these are rti (return from interrupt) and rts (return from subroutine).
  4. A handler may terminate program execution, meaning it never returns.
  5. The return address is not always the next instruction of the program but can also re-execute the current instruction.
  6. Exception handlers, especially those of the operating system, often have broader, if not full, privileges over system resources compared to user programs.

Types of Exceptions

We have already encountered one type of exception, interrupts, in earlier material. However, there are actually other types of exceptions.

Interrupt

An interrupt is caused by an asynchronous (time and program execution-independent) signal either internally within the processor or externally from a peripheral device. The processor checks the status of interrupt flags after executing each instruction. An interrupt does not interrupt the execution of a machine instruction already being executed. The setting of the interrupt flag in the status register is typically handled by the microarchitecture and/or firmware. When the interrupt flag is raised in the status register, the corresponding handler is executed. After the handler execution, the program resumes and executes its next instruction, depending on the interrupt type.
Hardware interrupts are referred to by two terms: IRQ (Interrupt Request) and NMI (Non-maskable Interrupt). IRQ is reserved for peripherals, connected to the processor via control circuits. NMI, on the other hand, is reserved for monitoring the internal operation of the central processing unit, such as preventing division by zero or handling memory errors, and thus has higher priority. When a hardware interrupt occurs, the corresponding handler in the firmware is executed similarly.
Example: The x86 family has 16 hardware interrupts (divided into two controllers).
Software interrupts, which are often system calls (see below), may have dedicated instructions in the machine language. For example, the x86 instruction int below. In x86, the interrupt call int 21 requests the BIOS service 0x2a to retrieve the date, calculated by the integrated real-time clock component.
mov ah,2ah # Service number in AH register
int 21h    # Interrupt executes desired service

System Call

Firmware services are partly managed by the operating system, accessed via system calls. Examples of system calls include I/O operations like reading a file or multitasking functionalities such as starting another process/program or terminating the current program. System calls are synchronous since they are invoked at specific points in the program.
System calls may be executed using dedicated machine instructions (trap instructions) or function calls (with parameters passed in registers). Additionally, some processors have protected instructions that only system calls can execute.
Example of a C program (linux/x86) using system calls instead of printf. The first parameter of the write function, 1, refers to the output stream ( stdout), typically the screen.
int main() {
   write(1,"hello world\n",13);  // printf("hello world\n");
   _exit(0);                     // return 0;
}
Observe that the C standard library (unistd.h) provides system calls for program use. Since they are lower-level functions, they require more details from the programmer.
The equivalent x86 assembly code would look like this. Note the syscall instruction for the system call.
string:
   .ascii "hello world\n" # String in ASCII format in memory
main:
   movq $1,%rax       # write is call number 1
   movq $1, %rdi      # Output stream (screen) is 1
   movq $string, %rsi # String address
   movq $13, %rdx     # Length of the string
   syscall            # Execute write

exit:
   movq $60,%rax      # exit is call number 60
   movq $0, %rdi      # Return value 0
   syscall
In assembly, all system call parameters are passed in registers, and the stack is not used. Parameters also have a specific order, where the %rax register contains the call number, etc. The return value is also provided in the %rax register.

Fault

A fault is an error condition that the handler may be able to fix. After executing the handler, the current program instruction is re-executed. If the handler cannot resolve the issue, the program execution is terminated with an error.
Example: A memory address reference that is not present in the processor's cache ( page fault). In this case, the handler retrieves the content of the memory address from main memory (or possibly from a lower-level cache) and stores it in the cache.

Abort

This exception occurs when an error condition arises in the system that cannot be resolved by the program/firmware/operating system (engl. abort). Examples include kernel crashes, faulty data (parity error) in memory, or hardware/component failure. Program execution halts at this point, and the program does not resume.
Example: The infamous Windows Blue Screen of Death, although similar issues also occur in Linux.

y86 Exceptions

In the y86 architecture, there are three internal exceptions:
  1. Machine language instruction halt, which stops program execution
  2. Invalid opcode INS
  3. Invalid memory address ADR
In the sequential y86, program execution halts, and the corresponding status bit is set. Instructions following this do not affect the processor's state.
In the y86 pipelined processor, exception handling is slightly more complex, as shown in the example of exception handling control logic:
main:
   xorq %rax,%rax
   jne target
   irmovq  $1,%rax
target:
   movl $13,%rbx     # invalid opcode (here, an x86 instruction)
However, exception handlers are not implemented in the y86 simulator. In y86, when an exception occurs, program execution halts, and subsequent instructions no longer alter the processor state.

Other bibliography

Please refer to the course book Bryant & O'Hallaron, Computer Systems: A Programmer's Perspective, 3rd edition. Chapter 8.

Conclusion

It is interesting to note that the fundamental idea behind firmware has remained the same for decades. However, as processor technology has advanced, exception handling in modern processors has become a rather complex matter.
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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).