C++ Program to Find Factorial of a Number

In this post, we will learn how to find the factorial of a number using C++ Programming language. But before that, let’s learn about factorials.

The factorial of a number is the product of all integers from 1 to that number. For example, the factorial of 5 is 5! = 5 x 4 x 3 x 2 x 1 = 120.

We will calculate the factorial of a number entered by the user using the following approaches:

  1. Using For Loop 
  2. Using While Loop

So, without further ado, let’s begin this tutorial.

C++ Program to Find Factorial of a Number

// C++ Program to Find Factorial of a Number
#include <iostream>
using namespace std;

int main(){
    int num, fact = 1;
    
    // Asking for input
    cout << "Enter a number to find the factorial: ";
    cin >> num;
    
    // Finding factorial of a number
    for (int i = 1; i <= num; i++){
        fact = fact * i;
    }
    
    // Displaying output
    cout << "Factorial of " << num << " is: " << fact << endl; 
    return 0;
}

Output

Enter a number to find the factorial: 4
Factorial of 4 is: 24

How Does This Program Work?

    int num, fact = 1;

In this program, we have declared two integer data type variables named num and fact. The fact variable has assigned a value of 1.

    // Asking for input
    cout << "Enter a number to find the factorial: ";
    cin >> num;

The user is asked to enter a number. The entered value gets stored in the num named variable.

    // Finding factorial of a number
    for (int i = 1; i <= num; i++){
        fact = fact * i;
    }

We use a for loop to calculate the factorial of the entered number. Suppose the user enters a number such that num = 4.

Now, to find the factorial of 4!, we perform:

  • 1st For Loop Iteration: for (int i = 1; i <= 4; i++)
  • fact = fact * i = 1 * 1 = 1.
  • 2nd For Loop Iteration: for (int i = 2; i <= 4; i++)
  • fact = fact * i = 1 * 2 = 2.
  • 3rd For Loop Iteration: for (int i = 3; i <= 4; i++)
  • fact = fact * i = 2 * 3 = 6.
  • 4th For Loop Iteration: for (int i = 4; i <= 4; i++)
  • fact = fact * i = 4 * 6 = 24.

5th For Loop Iteration: for (int i = 5; i <= 4; i++), here the condition is False, so the loop terminates and we get fact = 24.

    // Displaying output
    cout << "Factorial of " << num << " is: " << fact << endl; 

The factorial of the entered number is displayed on the screen using the cout statement.

C++ Program to Find Factorial of a Number Using While Loop

// C++ Program to Find Factorial of a Number Using While Loop
#include <iostream>
using namespace std;

int main(){
    int num, i = 1, fact = 1;
    
    // Asking for input
    cout << "Enter a number: ";
    cin >> num;
    
    // Calculating factorial using while loop
    while (i <= num){
        fact = fact * i;
        i++;
    }
    
    // Displaying output
    cout << "The factorial of " << num << " is: " << fact << endl;
    return 0;
}

Output

Enter a number: 6
The factorial of 6 is: 720

Conclusion

I hope after going through this post, you understand how to find the factorial of a number using C++ Programming language.

If you have any doubt regarding the program, feel free to contact us in the comment section. We will be delighted to assist you.

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