Factorial program in C

Simple program - without using User Define Function

/*C program to find factorial of a number.*/
 
#include <stdio.h>
 
int main()
{
    int num,i;
    long int fact;
  
    printf("Enter an integer number: ");
    scanf("%d",&num);
  
    /*product of numbers from num to 1*/
    fact=1;
    for(i=num; i>=1; i--)
        fact=fact*i;
         
    printf("\nFactorial of %d is = %ld",num,fact);
      
    return 0;
}

Output

Enter an integer number: 7

Factorial of 7 is = 5040

User Define Function

/*Using Function: C program to find factorial of a number.*/
 
#include <stdio.h>
 
/* function : factorial, to find factorial of a given number*/
 
long int factorial(int n)
{
    int i;
    long int fact=1;
 
    if(n==1) return fact;
 
    for(i=n;i>=1;i--)
        fact= fact * i;
 
    return fact;
}
  
int main()
{
    int num;
 
    printf("Enter an integer number :");
    scanf("%d",&num);
 
    printf("\nFactorial of %d is = %ld",num,factorial(num));
     
    return 0;
}

Output

Enter an integer number: 7

Factorial of 7 is = 5040

Using Recursion

//function for factorial
long int factorial(int n)
{   
    if(n==1)    return 1;
    return n*factorial(n-1);
}

Logic behind to implement these programs

• Variables for program - int to store number, long int to store factorial because factorial value is higher than integer value.
• Now, input the number.
• Run a loop from num to 1 and multiply the numbers in a variable called fact.
• And the fact will be the factorial after executing the loop.