C program to find factorial of a number using Recursion

What does the term "Factorial of a Number" mean?

In mathematics, factorial is the product of all positive integers that are less than or equal to a certain positive integer, and it is symbolised by that positive integer and an exclamation point. So, factorial seven is represented as 9!, which equals 9*8*7*6*5*4*3*2*1. Factorial 0 is equal to 1 in mathematics.

Example:

  12! =12*11*10*9*8*7*6*5*4*3*2*1
  17! =17*16*15*14*13*12*11*10*9*8*7*6*5*4*3*2*1

To find factorial of a given number in C, there are two ways:

1. Using Recursion
2. Using Loop

Factorial of a Number using Recursion:

This code asks the user to enter any integer number, calculates its factorial, and displays the results on the screen. To complete the work, we will utilize a recursive function which must be user defined. In order to determine the factorial of the input integer, the function "factorial" in this case calls itself recursively. The code includes user interaction, but if we don't want it, we can just provide an integer number to variable no and omit the scanf statement. In other words, we can change it as we like; the argument would remain the same in every situation.

Code:

// using recursion


#include<stdio.h>  
  
long long int factorial ( long int no )  
{  
  	if ( no == 0 )  //check whether the condition is true or false
    	return 1;  //if the number is zero it will return one
    	
	long long int fact = factorial ( no - 1 ); //storing the value of the recursive function in variable
    
	return no * fact;  //returning the value
}  
   
int main()  
{  
  long long int numb; //taking variable numb
  long long int f;  //taking variable f
  printf("Enter a number: ");  //put any integer number
  scanf( "%ld", & numb) ;  //value stores in numb variable 
   
  f = factorial ( numb );  //f stores the value of the factorial
  printf( "%ld is the factorial of %ld\n", f, numb );  //printing the factorial value of a number
  return 0;  
}

Output: (If user puts 9 as input)

Enter a number: 9
362880 is the factorial of 9

Output: (If user puts 11 as input)

Enter a number: 11
39916800 is the factorial of 11

Note: Remember that we can not find factorial of a large number as the value will be so large to store.

C Program to find factorial of a given number using loop:

Code:

//using loop


#include<stdio.h>  
int main()    
{    
 long long int index, facto=1, no;   //taking variables 
 printf("Enter a number: ");    //asks user for a integer value
  scanf("%ld", & no);    //stores value in "no" variable
    for (index = 1; index <= no; index ++) //using for loop
	{    
      facto = facto * index;   // logic
    }    
   
     printf("%ld is the factorial of %ld\n", facto, no );  //printing the factorial value of given number  
     return 0;  
}  

Output: (If user puts 12 as input)

Enter a number: 12
479001600 is the factorial of 12

Output: (If user puts 4 as input)

Enter a number: 4
24 is the factorial of 4