Recursion Base Case and Recursive Case in DSA C - Build from Scratch

Recursion Base Case and Recursive Case

📖 Scenario: Imagine you want to find the factorial of a number. Factorial means multiplying the number by all smaller numbers down to 1. For example, 4 factorial is 4 x 3 x 2 x 1 = 24.

🎯 Goal: You will write a recursive function in C that calculates the factorial of a number using a base case and a recursive case.

📋 What You'll Learn

Create a function called factorial that takes an integer n as input.

Use a base case where if n is 1, the function returns 1.

Use a recursive case where the function returns n multiplied by factorial(n - 1).

Call the factorial function with the value 5 and print the result.

💡 Why This Matters

🌍 Real World

Recursion is used in many places like calculating factorials, navigating file systems, and solving puzzles.

💼 Career

Understanding recursion helps in solving problems that require breaking down tasks into smaller similar tasks, common in software development and algorithm design.

1

Create the factorial function with base case

Write a function called factorial that takes an integer n and returns 1 if n is 1.

DSA C

# Write the factorial function with base case
int factorial(int n) {
    // Your code here
}

Hint

The base case stops the recursion. If n is 1, return 1.

2

Add the recursive case to factorial function

Inside the factorial function, add a recursive case that returns n * factorial(n - 1) when n is not 1.

DSA C

int factorial(int n) {
    if (n == 1) {
        return 1;
    }
    // Your code here
}

Hint

The recursive case calls factorial again with n - 1 and multiplies the result by n.

3

Call factorial function with 5

In the main function, call factorial with the value 5 and store the result in an integer variable called result.

DSA C

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

int main() {
    // Call factorial with 5 and store in result
    // Your code here
    return 0;
}

Hint

Use int result = factorial(5); to call the function and save the answer.

4

Print the factorial result

Add a printf statement in main to print the value of result with the message: "Factorial of 5 is: %d\n".

DSA C

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

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

Hint

Use printf("Factorial of 5 is: %d\n", result); to show the answer.