C Programming Practice Set 4 – Functions

Functions help us divide a large program into smaller, reusable blocks of code. They improve readability, reduce code duplication, and make debugging easier.

In this practice set, you'll solve problems using user-defined functions, recursion, return values, and parameter passing.

Each program includes:

• 🎯 Objective
• 💡 Problem Statement
• 💻 C Program
• ▶ Sample Input
• ✅ Sample Output
• 📚 Explanation

Program 1 — Function to Add Two Numbers

🎯 Objective

Create and call a simple user-defined function.

Program

cCopy
#include <stdio.h>

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

int main()
{
    int x, y;

    scanf("%d %d", &x, &y);

    printf("Sum = %d", add(x, y));

    return 0;
}

Sample Input

10 20

Sample Output

Sum = 30

Program 2 — Check Even or Odd Using Function

cCopy
#include <stdio.h>

void checkEvenOdd(int n)
{
    if(n % 2 == 0)
        printf("Even");
    else
        printf("Odd");
}

int main()
{
    int number;

    scanf("%d", &number);

    checkEvenOdd(number);

    return 0;
}

Program 3 — Find Largest of Two Numbers

cCopy
#include <stdio.h>

int largest(int a, int b)
{
    if(a > b)
        return a;

    return b;
}

int main()
{
    int x, y;

    scanf("%d %d", &x, &y);

    printf("%d", largest(x, y));

    return 0;
}

Program 4 — Factorial Using Function

cCopy
#include <stdio.h>

long long factorial(int n)
{
    long long fact = 1;

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

    return fact;
}

int main()
{
    int number;

    scanf("%d", &number);

    printf("%lld", factorial(number));

    return 0;
}

Sample Input

5

Sample Output

120

Program 5 — Prime Number Using Function

cCopy
#include <stdio.h>

int isPrime(int n)
{
    if(n <= 1)
        return 0;

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

    return 1;
}

int main()
{
    int number;

    scanf("%d", &number);

    if(isPrime(number))
        printf("Prime");
    else
        printf("Not Prime");

    return 0;
}

Program 6 — Fibonacci Series Using Function

cCopy
#include <stdio.h>

void fibonacci(int n)
{
    int first = 0;
    int second = 1;
    int next;

    for(int i = 1; i <= n; i++)
    {
        printf("%d ", first);

        next = first + second;
        first = second;
        second = next;
    }
}

int main()
{
    int n;

    scanf("%d", &n);

    fibonacci(n);

    return 0;
}

Program 7 — Swap Two Numbers (Call by Value)

cCopy
#include <stdio.h>

void swap(int a, int b)
{
    int temp = a;

    a = b;
    b = temp;
}

int main()
{
    int x = 10;
    int y = 20;

    swap(x, y);

    printf("%d %d", x, y);

    return 0;
}

Output

10 20

Explanation

The original variables remain unchanged because C passes arguments by value.

Program 8 — Swap Two Numbers (Call by Reference)

cCopy
#include <stdio.h>

void swap(int *a, int *b)
{
    int temp = *a;

    *a = *b;
    *b = temp;
}

int main()
{
    int x = 10;
    int y = 20;

    swap(&x, &y);

    printf("%d %d", x, y);

    return 0;
}

Output

20 10

Program 9 — Recursive Factorial

cCopy
#include <stdio.h>

long long factorial(int n)
{
    if(n == 0 || n == 1)
        return 1;

    return n * factorial(n - 1);
}

int main()
{
    int number;

    scanf("%d", &number);

    printf("%lld", factorial(number));

    return 0;
}

Program 10 — Recursive Fibonacci

cCopy
#include <stdio.h>

int fibonacci(int n)
{
    if(n <= 1)
        return n;

    return fibonacci(n - 1) + fibonacci(n - 2);
}

int main()
{
    int n;

    scanf("%d", &n);

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

    return 0;
}

Program 11 — Find Square Using Function

cCopy
#include <stdio.h>

int square(int n)
{
    return n * n;
}

int main()
{
    int number;

    scanf("%d", &number);

    printf("%d", square(number));

    return 0;
}

Program 12 — Find Cube Using Function

cCopy
#include <stdio.h>

int cube(int n)
{
    return n * n * n;
}

int main()
{
    int number;

    scanf("%d", &number);

    printf("%d", cube(number));

    return 0;
}

Program 13 — Sum of Digits Using Function

cCopy
#include <stdio.h>

int sumDigits(int n)
{
    int sum = 0;

    while(n != 0)
    {
        sum += n % 10;
        n /= 10;
    }

    return sum;
}

int main()
{
    int number;

    scanf("%d", &number);

    printf("%d", sumDigits(number));

    return 0;
}

Program 14 — Reverse Number Using Function

cCopy
#include <stdio.h>

int reverse(int n)
{
    int rev = 0;

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

    return rev;
}

int main()
{
    int number;

    scanf("%d", &number);

    printf("%d", reverse(number));

    return 0;
}

Program 15 — Calculator Using Functions

cCopy
#include <stdio.h>

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

int subtract(int a, int b)
{
    return a - b;
}

int multiply(int a, int b)
{
    return a * b;
}

float divide(int a, int b)
{
    return (float)a / b;
}

int main()
{
    int a, b;

    scanf("%d %d", &a, &b);

    printf("Addition = %d\n", add(a, b));
    printf("Subtraction = %d\n", subtract(a, b));
    printf("Multiplication = %d\n", multiply(a, b));
    printf("Division = %.2f\n", divide(a, b));

    return 0;
}

⭐ Practice Challenge

Solve these programs without looking at the solutions.

1. Find the GCD of two numbers using a function.
2. Find the LCM of two numbers using a function.
3. Check whether a number is an Armstrong number using a function.
4. Find the largest among three numbers using a function.
5. Print all prime numbers between two numbers using functions.
6. Calculate the power of a number using recursion.
7. Convert decimal to binary using a function.
8. Count vowels in a string using a function.
9. Find the average of N numbers using a function.
10. Build a menu-driven calculator using functions.

📚 Summary

In this practice set, you learned:

• Function declaration and definition
• Function calls
• Return values
• void functions
• Call by Value
• Call by Reference
• Recursion
• Function reuse

Functions make programs modular, reusable, and easier to maintain. Mastering them is essential before moving on to arrays, strings, and pointers.

🚀 What's Next?

In Practice Set 5 – Arrays, you'll solve problems such as:

• Array input and output
• Largest and smallest element
• Sum and average
• Array reversal
• Sorting
• Searching
• Matrix operations
• Frequency counting

Happy Coding with KauraX 💙