C program to find factorial of a given number using recursion

This C program is to find factorial of a given number using recursion.For example, factorial of a given number using recursion, is factorial(5) = 120.

Logic

We include one base case i.e when we have 0, we output the factorial as one and we have finished our program so we need to exit and a non base case i.e. start from n and keep multiplying n with a recursive call by decreasing n by 1.

Dry Run of the Program

Take input as n=4

We enter function fact()

int fact(int n)

n=4

if(n==0) false

else

return (n*fact(n-1));  i.e. return (4*fact(4-1))  i.e. return (4*fact(3))

A recursive call[fact(3)]

if(n==0) false

else

return (n*fact(n-1));  i.e. return (3*fact(3-1))  i.e. return (3*fact(2))

A recursive call[fact(2)]

if(n==0) false

else

return (n*fact(n-1));  i.e. return (2*fact(2-1))  i.e. return (2*fact(1))

A recursive call[fact(1)]

if(n==0) false

else

return (n*fact(n-1));  i.e. return (1*fact(1-1))  i.e. return (1*fact(0))

A recursive call[fact(0)]

if(n==0) true

return 1;

So now we will have

1*1 = 1    … fact(1)

2*1 = 2    …fact(2)

3*2 = 6    …fact(3)

4*6 = 24   …fact(4) ….final answer

Program

#include<stdio.h>
 
int fact(int n)
{
    if(n==0)
        return 1;
    else 
        return (n*fact(n-1));
}
 
void main()
{
    int num;
    printf("Enter the nth term\n");
    scanf("%d",&num);
    printf("Factorial(%d) = %d\n",num,fact(num));
}

Output