Programming in C

The Language of C

• C is a structured, procedural, compiled language created by Dennis Ritchie.
• Main properties relevant for exams: portability, efficiency, manual memory control via pointers.

Phases of Developing a C Program

• Edit: write source file `program.c`.
• Compile: `gcc -Wall -c program.c` produces `program.o` and shows compile errors/warnings.
• Link: `gcc program.o -o program` produces executable.
• Run: `./program` on Unix-like systems.

Importance of C

• Foundation for system software and many languages.
• Used for OS, compilers, embedded systems because of speed and low-level access.

Basic Structure of a C Program

• Preprocessor directives: `#include`, `#define`.
• Function definitions with `main()` as entry point.
• Variable declarations and statements.
• Return from `main` typically `return 0;` to signal success.

#include <stdio.h>

int main(void) {
    int a = 10;
    printf("Value of a = %d
", a);
    return 0;
}

Compiling and Executing

• Compile and link in one step: gcc program.c -o program.
• Enable warnings: gcc -Wall program.c -o program.
• Run executable: ./program.
• Typical compile-time errors: syntax error, undeclared identifier, type mismatch.

Key Concepts

• Data types and range: `int`, `float`, `double`, `char`.
• Operators: arithmetic, relational, logical, bitwise.
• Control flow: `if`, `if-else`, `switch`, loops (`for`, `while`, `do-while`).
• Functions: declaration, definition, call, parameter passing (by value).
• Arrays and strings: contiguous memory, null-terminated char arrays.
• Pointers: address-of `&`, dereference `*`, pointer arithmetic basics.

Programming Style (exam checklist)

• Indent consistently and use meaningful names for variables and functions.
• Comment nontrivial logic; avoid redundant comments for obvious code.
• Check return values for I/O functions when necessary.
• Use compiler warnings to find potential bugs.

Common Debugging Points

#include <stdio.h>

int main() {
    int a;
    printf("Enter number: ");
    scanf("%d", a);   // wrong: should be &a
    printf("Value is: %d", a)  // wrong: missing semicolon
    return 0;
}

scanf("%d", &a);
printf("Value is: %d", a);