C Programming Language Notes 💻

1. Introduction and Fundamentals

What is C?

• C is a general-purpose, procedural programming language developed in 1972 by Dennis Ritchie.
• It was designed to write the UNIX OS.
• Called a “middle-level language” for combining high- & low-level features.

Key Features:

• Simplicity and Efficiency
• Portability
• Structured Language
• Memory Management through Pointers
• Extensive Libraries

Basic Program Structure:

#include <stdio.h> // Preprocessor directive

int main() {
    printf("Hello, World!\n");
    return 0;
}

2. Data Types and Variables

Variables: Declaration & Initialization

int age;
age = 30;
int roll = 101;

Constants:

#define PI 3.14159
const float pi = 3.14159;

3. Operators

• Arithmetic: +, -, *, /, %, ++, --
• Relational: ==, !=, >, <, >=, <=
• Logical: &&, ||, !
• Assignment: =, +=, -=, *=, /=
• Bitwise: &, |, ^, ~, <<, >>
• Ternary: condition ? true : false;

4. Control Flow

Decision Making:

switch (expression) {
    case 1:
        // code
        break;
    default:
        // code
}

Loops: for, while, do-while

for(int i=0; i<5; i++) {
    printf("%d", i);
}

5. Functions

int add(int a, int b) {   // Definition
    return a + b;
}

int main() {
    int sum = add(5, 3);   // Call
    printf("%d", sum);
    return 0;
}

6. Arrays and Strings

int numbers[5] = {1,2,3,4,5};
printf("%d", numbers[0]);

char name[20] = "John Doe";
printf("%s", name);

7. Pointers

int x = 10;
int *ptr = &x;
printf("%d", *ptr);

8. Structures and Unions

struct Student {
    int id;
    char name[50];
    float gpa;
};

struct Student s1;
s1.id = 101;

9. File Handling

FILE *fp = fopen("data.txt", "w");
fprintf(fp, "Hello File!");
fclose(fp);