1. The Main Function

The main function serves as the antry point for all C programs. Every C program must contain exactly one main function.

#include <stdio.h>

int main(void)  // Standard compliant declaration
{
    printf("Welcome to C programming\n");
    return 0;    // Indicates successful execution
}

Common variations of main function declarations:

int main() { ... }
int main(void) { ... }

2. Output Functions

The printf function displays formatted output to the standard output device:

#include <stdio.h>

int main()
{
    printf("Displaying formatted output\n");
    printf("Integer: %d, Character: %c\n", 42, 'A');
    return 0;
}

3. Standard Library Functions

C provides numerous built-in functions through standard libraries. These require appropriate header files:

#include <math.h>    // Math functions
#include <string.h>  // String operations

4. Reserved Keywords

C language defines 32 reserved keywords that cannot be used as identifiers:

auto    double  int     struct
break   else    long    switch
case    enum    register typedef
char    extern  return  union
const   float   short   unsigned
continue for     signed  void
default goto    sizeof  volatile
do      if      static  while

5. Character Encoding

C uses ASCII encoding for character representation:

printf("ASCII code for 'A': %d\n", 'A');  // Outputs 65
printf("Character for 97: %c\n", 97);     // Outputs 'a'

6. String Handling

Strings in C are null-terimnated character arrays:

char message[] = "Hello";  // Actually stores 'H','e','l','l','o','\0'
printf("%s\n", message);   // Prints until null character

7. Escape Sequences

Special character combinations for formatting:

printf("New\nLine\tTab\\Backslash\n");
printf("Alert\aBeep\bBackspace\rCarriageReturn");

8. Statement Types

C programs consist of several statement types:

• Expression statements (a = b + c;)
• Function calls (printf(...);)
• Control flow (if, for, while)
• Compound statements ({...})

9. Code Documentation

C supports two comment styles:

/* Multi-line comment 
   spanning several lines */

// Single-line comment
int x = 5;  // End-of-line comment