Factorial Using Recursion in DSA C - Build from Scratch

Factorial Using Recursion

📖 Scenario: Imagine you want to calculate the factorial of a number, which is the product of all positive integers up to that number. For example, factorial of 5 is 5 x 4 x 3 x 2 x 1 = 120.Using recursion, a function can call itself to solve smaller parts of the problem until it reaches the simplest case.

🎯 Goal: You will build a C program that calculates the factorial of a given number using a recursive function.

📋 What You'll Learn

Create a recursive function called factorial that takes an integer n and returns the factorial of n.

Use a base case in the recursion where factorial of 0 is 1.

Call the factorial function with the number 5 and store the result.

Print the result in the format: Factorial of 5 is 120.

💡 Why This Matters

🌍 Real World

Calculating factorial is useful in mathematics, statistics, and computer science problems like permutations and combinations.

💼 Career

Understanding recursion is fundamental for many programming tasks and technical interviews.

1

Create the main function and declare the number

Write a main function and declare an integer variable called number with the value 5.

DSA C

int main() {
    // Your code here
}

Hint

The main function is the starting point of a C program. Declare int number = 5; inside it.

2

Write the recursive factorial function

Write a recursive function called factorial that takes an integer n and returns an integer. Use the base case: if n == 0, return 1. Otherwise, return n * factorial(n - 1).

DSA C

int main() {
    int number = 5;
    return 0;
}

// Your code here

Hint

The function calls itself with n - 1 until it reaches 0, then returns 1.

3

Call the factorial function and store the result

Inside the main function, call factorial(number) and store the result in an integer variable called result.

DSA C

int factorial(int n) {
    if (n == 0) {
        return 1;
    } else {
        return n * factorial(n - 1);
    }
}

int main() {
    int number = 5;
    // Your code here
    return 0;
}

Hint

Store the factorial of number in result by calling factorial(number).

4

Print the factorial result

Add a printf statement inside main to print: Factorial of 5 is 120 using the variables number and result.

DSA C

int factorial(int n) {
    if (n == 0) {
        return 1;
    } else {
        return n * factorial(n - 1);
    }
}

int main() {
    int number = 5;
    int result = factorial(number);
    // Your code here
    return 0;
}

Hint

Use printf("Factorial of %d is %d\n", number, result); to print the output.