C Programming

Introduction

What is C Language?

C is one of the oldest and most widely-used programming languages in the world. It was developed in the early 1970s at Bell Labs. Almost every operating system — including Linux and Windows — is written using C or C-based languages.

If you're learning programming for the first time, C is an excellent starting point. It teaches you how computers actually work — memory, variables, logic, and how programs execute line by line.

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Why learn C first? C teaches the fundamentals that every other language builds on — variables, loops, functions, memory. Once you know C, learning Python, Java, or C++ becomes much easier.

Where is C used?

Area	Example
Operating Systems	Linux kernel, Windows core are written in C
Embedded Systems	Microcontrollers, Arduino, hardware drivers
System Tools	Compilers, database engines (MySQL core)
Game Development	Game engines and performance-critical code
Learning Foundation	First language taught in CS programs worldwide

Getting Ready

Setup & Install

You have two options — write code online (nothing to install) or install a compiler on your computer. Both work fine for learning.

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Online Compiler

Run C code in your browser. No installation needed. Best for beginners.

OnlineGDB →
Programiz →

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Dev-C++ (Offline)

Simple IDE for Windows. Classic choice for beginners. Easy to install.

Download Dev-C++ →

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VS Code + GCC

Professional setup. Lightweight editor with full GCC compiler support.

Download VS Code →
MinGW (GCC) →

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Recommendation: Start with OnlineGDB — no setup required, runs instantly. Once you're comfortable with the basics, install Dev-C++ or VS Code for offline practice.

How a C program runs

Every C program goes through these steps before you see output:

1Write code in a .c file — e.g. hello.c
2Compile — the compiler (GCC) converts your code to machine language
3Link — connects your code with library functions like printf
4Run — the executable file runs and shows output

Practical 1

Hello World Start Here

Every programmer writes this first. It teaches you the basic structure of a C program — what every file must contain before anything else can work.

hello.c

#include <stdio.h>    // standard input/output library

int main() {
    printf("Hello, World!\n");   // print to screen
    return 0;                    // 0 means program ran successfully
}

▶ OUTPUT

Hello, World!

Line by line explanation

Line	What it does
#include <stdio.h>	Imports the standard library so you can use printf and scanf
int main()	Every C program starts execution from main(). The int means it returns a number.
printf("...")	Prints text to the screen. \n moves to the next line.
return 0;	Tells the OS the program finished without errors.

Practical 2

Variables & Data Types

A variable is a named box that stores data. Before using a variable in C, you must declare its type — this tells the compiler how much memory to reserve and what kind of data it will hold.

Type	Stores	Example	Size
int	Whole numbers	5, -10, 100	4 bytes
float	Decimal numbers	3.14, -2.5	4 bytes
double	Precise decimals	3.14159265	8 bytes
char	Single character	'A', 'z', '5'	1 byte

variables.c

#include <stdio.h>

int main() {
    int    age    = 18;
    float  marks  = 87.5;
    char   grade  = 'A';

    printf("Age: %d\n", age);
    printf("Marks: %.1f\n", marks);
    printf("Grade: %c\n", grade);

    return 0;
}

▶ OUTPUT

Age: 18
Marks: 87.5
Grade: A

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Format specifiers: %d = integer, %f = float, %c = character, %s = string. These go inside printf/scanf to match the variable type.

Practical 3

Input & Output

printf() prints to the screen. scanf() reads input from the keyboard. Together, these two functions handle all basic interaction with the user.

input-output.c

#include <stdio.h>

int main() {
    int num1, num2, sum;

    printf("Enter first number: ");
    scanf("%d", &num1);       // & means "address of" num1

    printf("Enter second number: ");
    scanf("%d", &num2);

    sum = num1 + num2;
    printf("Sum = %d\n", sum);

    return 0;
}

▶ OUTPUT

Enter first number: 10
Enter second number: 25
Sum = 35

⚠️

Common mistake: Forgetting & before the variable name in scanf. Always write scanf("%d", &variable) — the ampersand is required.

Practical 4

Operators & Expressions

Operators perform operations on variables and values. C has arithmetic, relational, and logical operators.

Operator	Name	Example	Result
+	Addition	10 + 3	13
-	Subtraction	10 - 3	7
*	Multiplication	10 * 3	30
/	Division	10 / 3	3 (integer division)
%	Modulus (remainder)	10 % 3	1
==	Equal to	5 == 5	1 (true)
!=	Not equal	5 != 3	1 (true)
>	Greater than	7 > 4	1 (true)

operators.c

#include <stdio.h>

int main() {
    int a = 17, b = 5;

    printf("a + b = %d\n", a + b);
    printf("a - b = %d\n", a - b);
    printf("a * b = %d\n", a * b);
    printf("a / b = %d\n", a / b);   // integer division = 3
    printf("a %% b = %d\n", a % b);  // remainder = 2

    return 0;
}

▶ OUTPUT

a + b = 22
a - b = 12
a * b = 85
a / b = 3
a % b = 2

Practical 5

Decision Making

Programs need to make decisions based on conditions. C provides if, if-else, and switch for this.

if / else

if-else.c

#include <stdio.h>

int main() {
    int marks;
    printf("Enter marks: ");
    scanf("%d", &marks);

    if (marks >= 90) {
        printf("Grade: A+\n");
    } else if (marks >= 80) {
        printf("Grade: A\n");
    } else if (marks >= 70) {
        printf("Grade: B\n");
    } else if (marks >= 60) {
        printf("Grade: C\n");
    } else {
        printf("Grade: Fail\n");
    }

    return 0;
}

▶ OUTPUT

Enter marks: 85
Grade: A

switch statement

Use switch when comparing one variable against multiple fixed values — cleaner than many else-if chains.

switch.c — Simple Calculator

#include <stdio.h>

int main() {
    int a, b;
    char op;

    printf("Enter: num1 operator num2\n");
    scanf("%d %c %d", &a, &op, &b);

    switch (op) {
        case '+': printf("Result = %d\n", a + b); break;
        case '-': printf("Result = %d\n", a - b); break;
        case '*': printf("Result = %d\n", a * b); break;
        case '/':
            if (b != 0) printf("Result = %d\n", a / b);
            else printf("Error: Division by zero\n");
            break;
        default: printf("Unknown operator\n");
    }

    return 0;
}

▶ OUTPUT

Enter: num1 operator num2
8 * 5
Result = 40

Practical 6

Loops

Loops repeat a block of code multiple times. C has three types — for, while, and do-while.

for loop — Multiplication Table

for-loop.c

#include <stdio.h>

int main() {
    int n;
    printf("Enter a number: ");
    scanf("%d", &n);

    for (int i = 1; i <= 10; i++) {
        printf("%d x %d = %d\n", n, i, n * i);
    }

    return 0;
}

▶ OUTPUT

Enter a number: 5
5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
...
5 x 10 = 50

while loop

while-loop.c — Sum of digits

#include <stdio.h>

int main() {
    int num, sum = 0, digit;

    printf("Enter a number: ");
    scanf("%d", &num);

    while (num != 0) {
        digit = num % 10;    // get last digit
        sum += digit;
        num /= 10;            // remove last digit
    }

    printf("Sum of digits = %d\n", sum);
    return 0;
}

▶ OUTPUT

Enter a number: 456
Sum of digits = 15

do-while loop

Runs the body at least once, then checks the condition. Useful for menus.

do-while.c

#include <stdio.h>

int main() {
    int n = 1;

    do {
        printf("%d ", n);
        n++;
    } while (n <= 5);

    printf("\n");
    return 0;
}

▶ OUTPUT

1 2 3 4 5

Practical 7

Functions

A function is a reusable block of code that performs a specific task. Instead of writing the same code multiple times, you write it once as a function and call it whenever needed.

functions.c — Add two numbers

#include <stdio.h>

// Function declaration
int add(int a, int b);

int main() {
    int x = 10, y = 20;
    int result = add(x, y);    // function call
    printf("Sum = %d\n", result);
    return 0;
}

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

▶ OUTPUT

Sum = 30

Recursion

A function that calls itself is called recursive. It must have a base condition to stop, otherwise it runs forever.

recursion.c — Factorial

#include <stdio.h>

int factorial(int n) {
    if (n == 0 || n == 1)
        return 1;              // base condition
    return n * factorial(n - 1);  // recursive call
}

int main() {
    int n;
    printf("Enter n: ");
    scanf("%d", &n);
    printf("%d! = %d\n", n, factorial(n));
    return 0;
}

▶ OUTPUT

Enter n: 5
5! = 120

Practical 8

Arrays

An array stores multiple values of the same type in a single variable. Instead of creating 10 separate variables for 10 numbers, you create one array of size 10.

arrays.c — Store and display marks

#include <stdio.h>

int main() {
    int marks[5];
    int sum = 0;

    printf("Enter 5 marks:\n");
    for (int i = 0; i < 5; i++) {
        scanf("%d", &marks[i]);
        sum += marks[i];
    }

    printf("Total = %d\n", sum);
    printf("Average = %.1f\n", sum / 5.0);

    return 0;
}

▶ OUTPUT

Enter 5 marks:
70 80 90 85 75
Total = 400
Average = 80.0

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Array indexing starts at 0. An array int marks[5] has elements at positions 0, 1, 2, 3, 4. Accessing marks[5] goes out of bounds and causes undefined behavior.

Practice

Important Programs Exam Ready

These are the most commonly asked C programs in exams and lab practicals. Each one builds on the concepts covered above. Click any program to expand it.

Loops Factorial of a Number (using loop) ▼

Calculate n! using a for loop. Factorial of 5 = 5×4×3×2×1 = 120.

factorial-loop.c

#include <stdio.h>

int main() {
    int n, fact = 1;
    printf("Enter n: ");
    scanf("%d", &n);

    for (int i = 1; i <= n; i++)
        fact *= i;

    printf("%d! = %d\n", n, fact);
    return 0;
}

▶ OUTPUT

Enter n: 5
5! = 120

Loops Fibonacci Series ▼

Print the Fibonacci series up to n terms. Each number is the sum of the two before it: 0, 1, 1, 2, 3, 5, 8...

fibonacci.c

#include <stdio.h>

int main() {
    int n, a = 0, b = 1, c;

    printf("How many terms? ");
    scanf("%d", &n);

    printf("Fibonacci: ");
    for (int i = 1; i <= n; i++) {
        printf("%d ", a);
        c = a + b;
        a = b;
        b = c;
    }
    printf("\n");
    return 0;
}

▶ OUTPUT

How many terms? 7
Fibonacci: 0 1 1 2 3 5 8

Decision + Loops Check Prime Number ▼

A prime number is divisible only by 1 and itself. Check if a given number is prime.

prime.c

#include <stdio.h>

int main() {
    int n, isPrime = 1;

    printf("Enter a number: ");
    scanf("%d", &n);

    if (n < 2) isPrime = 0;

    for (int i = 2; i < n; i++) {
        if (n % i == 0) {
            isPrime = 0;
            break;
        }
    }

    if (isPrime)
        printf("%d is a Prime number\n", n);
    else
        printf("%d is NOT a Prime number\n", n);

    return 0;
}

▶ OUTPUT

Enter a number: 13
13 is a Prime number

Loops + Math Reverse a Number & Check Palindrome ▼

Reverse the digits of a number. If reversed == original, it's a palindrome (e.g. 121, 1331).

palindrome.c

#include <stdio.h>

int main() {
    int num, original, rev = 0;

    printf("Enter a number: ");
    scanf("%d", &num);
    original = num;

    while (num != 0) {
        rev = rev * 10 + (num % 10);
        num /= 10;
    }

    printf("Reversed: %d\n", rev);

    if (original == rev)
        printf("%d is a Palindrome\n", original);
    else
        printf("%d is NOT a Palindrome\n", original);

    return 0;
}

▶ OUTPUT

Enter a number: 121
Reversed: 121
121 is a Palindrome

Arrays Largest & Smallest in an Array ▼

Find the maximum and minimum values from an array entered by the user.

largest-smallest.c

#include <stdio.h>

int main() {
    int n, arr[50];

    printf("How many numbers? ");
    scanf("%d", &n);

    printf("Enter %d numbers:\n", n);
    for (int i = 0; i < n; i++)
        scanf("%d", &arr[i]);

    int max = arr[0], min = arr[0];
    for (int i = 1; i < n; i++) {
        if (arr[i] > max) max = arr[i];
        if (arr[i] < min) min = arr[i];
    }

    printf("Largest  = %d\n", max);
    printf("Smallest = %d\n", min);
    return 0;
}

▶ OUTPUT

How many numbers? 5
Enter 5 numbers:
34 12 78 56 90
Largest  = 90
Smallest = 12

Arrays Bubble Sort ▼

Sort an array in ascending order by repeatedly swapping adjacent elements that are in the wrong order.

bubble-sort.c

#include <stdio.h>

int main() {
    int n, arr[50], temp;

    printf("How many numbers? ");
    scanf("%d", &n);

    for (int i = 0; i < n; i++)
        scanf("%d", &arr[i]);

    // Bubble sort
    for (int i = 0; i < n-1; i++) {
        for (int j = 0; j < n-i-1; j++) {
            if (arr[j] > arr[j+1]) {
                temp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = temp;
            }
        }
    }

    printf("Sorted: ");
    for (int i = 0; i < n; i++)
        printf("%d ", arr[i]);
    printf("\n");
    return 0;
}

▶ OUTPUT

How many numbers? 5
64 34 25 12 22
Sorted: 12 22 25 34 64

Arrays Linear Search ▼

Search for a value in an array by checking each element one by one from start to end.

linear-search.c

#include <stdio.h>

int main() {
    int arr[] = {10, 25, 38, 47, 55};
    int n = 5, target, found = 0;

    printf("Enter number to search: ");
    scanf("%d", &target);

    for (int i = 0; i < n; i++) {
        if (arr[i] == target) {
            printf("Found at index %d\n", i);
            found = 1;
            break;
        }
    }

    if (!found)
        printf("Number not found\n");

    return 0;
}

▶ OUTPUT

Enter number to search: 38
Found at index 2

Nested Loops Star Pattern (Right Triangle) ▼

Print a right-triangle star pattern using nested loops. Classic exam question for testing loop understanding.

pattern.c

#include <stdio.h>

int main() {
    int n;
    printf("Enter rows: ");
    scanf("%d", &n);

    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= i; j++) {
            printf("* ");
        }
        printf("\n");
    }
    return 0;
}

▶ OUTPUT (n=5)

*
* *
* * *
* * * *
* * * * *

Loops Sum & Average of N Numbers ▼

Read N numbers from the user and calculate their sum and average.

sum-average.c

#include <stdio.h>

int main() {
    int n, num, sum = 0;

    printf("How many numbers? ");
    scanf("%d", &n);

    for (int i = 1; i <= n; i++) {
        printf("Enter number %d: ", i);
        scanf("%d", &num);
        sum += num;
    }

    printf("Sum     = %d\n", sum);
    printf("Average = %.2f\n", (float)sum / n);
    return 0;
}

▶ OUTPUT

How many numbers? 3
Enter number 1: 10
Enter number 2: 20
Enter number 3: 30
Sum     = 60
Average = 20.00

Decision + Loops Count Even & Odd Numbers in Array ▼

Read an array and count how many numbers are even and how many are odd using the modulus operator.

even-odd.c

#include <stdio.h>

int main() {
    int n, arr[50], even = 0, odd = 0;

    printf("How many numbers? ");
    scanf("%d", &n);

    for (int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
        if (arr[i] % 2 == 0)
            even++;
        else
            odd++;
    }

    printf("Even numbers: %d\n", even);
    printf("Odd  numbers: %d\n", odd);
    return 0;
}

▶ OUTPUT

How many numbers? 6
1 2 3 4 5 6
Even numbers: 3
Odd  numbers: 3

⭐

More programs coming. This page is regularly updated. Bookmark it and check back for more practicals including string programs, 2D arrays, and number system conversions.

What is C Language?

Where is C used?

Setup & Install

Online Compiler

Dev-C++ (Offline)

VS Code + GCC

How a C program runs

Hello World Start Here

Line by line explanation

Variables & Data Types

Input & Output

Operators & Expressions

Decision Making

if / else

switch statement

Loops

for loop — Multiplication Table

while loop

do-while loop

Functions

Recursion

Arrays

Important Programs Exam Ready

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