Program for factorial of a number in C program

Given with the number n the task is to calculate the factorial of a number. Factorial of a number is calculated by multiplying the number with its smallest or equal integer values.

Factorial is calculated as −

0! = 1
1! = 1
2! = 2X1 = 2
3! = 3X2X1 = 6
4! = 4X3X2X1= 24
5! = 5X4X3X2X1 = 120
.
.
.
N! = n * (n-1) * (n-2) * . . . . . . . . . .*1

Example

Input 1 -: n=5
   Output : 120
Input 2 -: n=6
   Output : 720

There are multiple methods that can be used −

• Through the loops
• Through recursion which is not at all effective
•  Through a function

Given below is the implementation using functions

Algorithm

Start
Step 1 -> Declare function to calculate factorial
   int factorial(int n)
      IF n = 0
         return 1
      End
      return n * factorial(n - 1)
step 2 -> In main()
   Declare variable as int num = 10
   Print factorial(num))
Stop

Using C

Example

#include<stdio.h>
// function to find factorial
int factorial(int n){
   if (n == 0)
   return 1;
   return n * factorial(n - 1);
}
int main(){
   int num = 10;
   printf("Factorial of %d is %d", num, factorial(num));
   return 0;
}

Output

Factorial of 10 is 3628800

Using C++

Example

#include<iostream>
using namespace std;
// function to find factorial
int factorial(int n){
   if (n == 0)
   return 1;
   return n * factorial(n - 1);
}
   int main(){
   int num = 7;
   cout << "Factorial of " << num << " is " << factorial(num) << endl;
   return 0;
}

Output

Factorial of 7 is 5040