Question

The factorial of a number, say N is the product of first N natural numbers. Thus, factorial of 5 can be obtained by taking the product of 5 and factorial of 4. Similarly factorial of 4 be found out by taking the product of 4 and factorial of 3. At last the factorial of 1 is 1 itself. Which technique is applicable to find the factorial of a number in this fashion? Write a C++ function to implement this technique. Also explain the working of the function by giving the number 5 as input.

Answer 1

A function calls itself is known as recursion.

# include<iostream>

using namespace std; 

int fac(int); 

int main()

{

int n;

cout<<"enter a number";

cin>>n;

cout<<fac(n);

}

int fac(int n)

{

if(n==1)

return (1);

else

return (n*fac(n-1));

}

The working of this program is as follows. If the value of n is 5 then it calls the function as fac(5). The function returns value 5*fac(4). That means this function calls the function again and returns 5*4*fac(3). This process continues until the value n=1. So the result is 5*4*3*2*1 = 120.