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In this example, you will learn to find the factorial of a non-negative integer entered by the user using recursion.

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To understand this example, you should have the knowledge of the following C programming topics:

• C Functions
• C User-defined functions
• C Recursion

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The factorial of a positive number n is given by:

factorial of n (n!) = 1 * 2 * 3 * 4 *...  * n

The factorial of a negative number doesn’t exist. And the factorial of 0 is 1.

You will learn to find the factorial of a number using recursion in this example. Visit this page to learn how you can find the factorial of a number using a loop.

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Factorial of a Number Using Recursion

#include
long int multiplyNumbers(int n);
int main() {
    int n;
    printf("Enter a positive integer: ");
    scanf("%d",&n);
    printf("Factorial of %d = %ld", n, multiplyNumbers(n));
    return 0;
}

long int multiplyNumbers(int n) {
    if (n>=1)
        return n*multiplyNumbers(n-1);
    else
        return 1;
}

Output

Enter a positive integer: 6
Factorial of 6 = 720

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Suppose the user entered 6.

Initially, multiplyNumbers() is called from main() with 6 passed as an argument.

Then, 5 is passed to multiplyNumbers() from the same function (recursive call). In each recursive call, the value of argument n is decreased by 1.

When the value of n is less than 1, there is no recursive call and the factorial is returned ultimately to the main() function.