Write a C Program to find factorial by recursion and iteration methods

Factorial of a Number : :

A factorial of a number x is defined as the product of x and all positive integers below x.  A factorial is product of all the number from 1 to the user specified number.

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 and iterative methods in this example.

1. Using Recursion : :

We will use a recursive user defined function to perform the task. Here we have a function fact( )  that calls itself in a recursive manner to find out the factorial of input number.

2. Using Iterative : :

To calculate the factorial in a for loop, it seems like all we would have to do is start from x and then multiply by all integer values below x, and just hold that value until we are done iterating.

Below is the source code for C Program to find factorial by recursion and iteration methods which is successfully compiled and run on Windows System to produce desired output as shown below :

SOURCE CODE : :

/* Program to find the factorial of a number by recursion and iteration method*/



#include<stdio.h>
long int fact(int n);
long int Ifact(int n);

int main( )
{
        int num;
        printf("Enter a number : ");
        scanf("%d", &num);

        printf("\nUsing Recursion :: \n");
        if(num<0)
                printf("No factorial for negative number\n");
        else
                printf("Factorial of %d is %ld\n", num, fact(num) );

    printf("\nUsing Iterative :: \n");

        if(num<0)
                printf("No factorial for negative number\n");
        else
                printf("Factorial of %d is %ld\n", num, Ifact(num) );

                return 0;
}/*End of main()*/

/*Recursive*/
long int fact(int n)
{
        if(n == 0)
                return(1);
        return(n * fact(n-1));
}/*End of fact()*/

/*Iterative*/
long int Ifact(int n)
{
        long fact=1;
        while(n>0)
        {
                fact = fact*n;
                n--;
        }
        return fact;
}/*End of ifact()*/

OUTPUT  : :

Enter a number : 8

Using Recursion ::
Factorial of 8 is 40320

Using Iterative ::
Factorial of 8 is 40320