C Program to Find Factorial of Number

In this tutorial, we will learn about how to find and print factorial of any given number with and without using function. Here we have also created a recursive function to find out the factorial of any number. Here are the list of programs you will go through:

  • Find Factorial of Given Number
  • Find Factorial of Given Number using Function
  • Find Factorial of Given Number using Recursion
  • Find Factorial of all Numbers in Given Range

But before starting these programs, let's understand how factorial of a number gets calculated.

How to Find Factorial of any Number ?

To find factorial f of any number say n, use the formula

Factorial of n (n!) = (n)*(n-1)*(n-2)*....*3*2*1

Or

n! = 1*2*3*....*(n-2)*(n-1)*n

For example, find factorial of 5, using the above formula

5! = 5*4*3*2*1
   = 120

So factorial of 5 is 120. Now let's move on and implement it in a C program.

Find Factorial of Given Number in C

To find the factorial of any given number in C programming, you have to ask from user to enter the number. Now find the factorial of that number using above formula as shown in the program given below. As you can see from the formula, if a number is n, then multiplication gets occurred for n times.

Or for example, if 5 is the number, then multiplication gets occurred 5 times, that is 5*4*3*2*1. So here it is required to create loop that runs n number of times

#include<stdio.h>
#include<conio.h>
int main()
{
    int num, i, fact=1;
    printf("Enter any number: ");
    scanf("%d", &num);
    for(i=num; i>0; i--)
        fact = fact*i;
    printf("\nFactorial of %d = %d", num, fact);
    getch();
    return 0;
}

As the program was written under Code::Blocks IDE, therefore after successful build and run you will get the following output:

c program find factorial of number

Now supply any number say 5 and press ENTER key to see the factorial of 5 as output as shown here:

find factorial c

Program Explained

  • Get the number as input say 5 using scanf() function
  • Create a for loop starting from the number say 5 in this case
  • Continue running the for loop until the number (here variable i holds the value of num) becomes 0
  • If user has provided the number 5 as input, then at first run of the for loop, i holds 5 which is greater than 0, and here fact holds 1 as its initial value, therefore fact*i or 5*1 or 5 is initialized to fact variable
  • At second run i is decremented and holds the value 4 which is again greater than 0, therefore inside the loop, fact*i or 5*4 or 20 is initialized to fact. In same way, at third, fourth, and fifth run, fact holds its final value as 5*4*3*2*1 or 120. At sixth time, when i gets decremented and becomes 0 which is not greater than 0, therefore the condition evaluates to false, therefore the program flow goes out of the for loop
  • Now print the value of fact variable, that contains the factorial value say 120 of given number say 5

Find Factorial of a Number using Function

This program does the same job, but using user-defined function findFact(). To learn about function, then refer to its separate tutorial where you can go for its in-depth tutorial.

#include<stdio.h>
#include<conio.h>
int findFact(int);
int main()
{
    int num, fact;
    printf("Enter any number: ");
    scanf("%d", &num);
    fact = findFact(num);
    printf("\nFactorial of %d = %d", num, fact);
    getch();
    return 0;
}
int findFact(int n)
{
    int i=n, f=1;
    while(i>0)
    {
        f = f*i;
        i--;
    }
    return f;
}

Find Factorial of a Number using Recursion

Here is another program that will calculate the factorial of any given number using recursive function:

#include<stdio.h>
#include<conio.h>
int findFact(int);
int main()
{
    int num, fact;
    printf("Enter the number: ");
    scanf("%d", &num);
    fact = findFact(num);
    printf("Factorial = %d", fact);
    getch();
    return 0;
}
int findFact(int val)
{
    if(val==1)
        return val;
    else
        return val*findFact(val-1);
}

Here is the final snapshot of the sample run:

c factorial using recursive function

Program Explained

  • Declare the function with one argument to pass the given value or number by user
  • Inside the main function, receive number as input and call the function in such a way the function will initialize its returning value to the variable that contains the factorial value of given number say fact
  • In recursive function definition, we have checked whether the value or number (passed through argument) is equal to 1 or not, if it is, then return the value of variable val, otherwise return val*findFact(val-1)
  • For example, if user has supplied 5 as input, then 5 is the argument that gets passed to the recursive function, at first time, 5 is not equal to 1, therefore the program flow goes to the else block's statement, here the returning value is 5*findFact(5-1) or 5*findFact(4). As we have return the function itself, therefore the function findFact() gets called itself (that is called recursive function).
  • The function is called with argument 4, therefore again 4 is not equal to 1, then again the program flow goes to the else block's statement, therefore the return value will be this time, return 5*4*findFact(4-3) or 20*findFact(3)
  • In same way the final return value before the argument value becomes 1 will be return 120*findFact(2-1) or 120*findFact(1)
  • At last when the argument value is 1, then the program flow goes to the if block's statement, that return only the value of variable val that holds the factorial value say 120 of the number that has passed at first time as argument to the function say 5 here
  • Finally 120 is initialized to the variable fact inside the main() function
  • Print the value of fact variable, that contains the factorial value of the given number

If you are not satisfied with above explanation. Then I recommend you to refer Recursion in C tutorial. There you will of course understand all about it, that how recursion works.

Find Factorial of all Numbers in Given Range

Now this is the last program that will find factorial of all numbers in given range. For example, if user enters 1 and 10 as two number (the range). Then the program will find and prints factorial of all numbers from 1 to 10.

#include<stdio.h>
#include<conio.h>
int findFact(int);
int main()
{
    int num1, num2, i;
    long int fact;
    printf("Enter Range: ");
    scanf("%d %d", &num1, &num2);
    if(num1<num2)
    {
        for(i=num1; i<=num2; i++)
        {
            fact = findFact(i);
            printf("\nFactorial of %d = %ld", i, fact);
        }
    }
    else
    {
        for(i=num2; i<=num1; i++)
        {
            fact = findFact(i);
            printf("\nFactorial of %d = %ld", i, fact);
        }
    }
    getch();
    return 0;
}
int findFact(int n)
{
    int i=n;
    long int f=1;
    while(i>0)
    {
        f = f*i;
        i--;
    }
    return f;
}

Here is its sample run:

find factorial of all number in range c

Same Program in Other Languages

C Online Test


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