Find Factorial of a Number Using Iteration in C++

In this article, we'll show you how to write a C++ program to find the factorial of a number using an iterative approach. The factorial of a number is the result of multiplying all the positive integers from 1 to that number. It is written as n! and is commonly used in mathematics and programming.

Let's understand this with a few examples:

//Example 1
Input:
5
The factorial of 5 is: 5 * 4 * 3 * 2 * 1 = 120
Output:
120

//Example 2
Input:
6
The factorial of 6 is: 6 * 5 * 4 * 3 * 2 * 1 = 720
Output:
720

Using Iteration for Finding the Factorial

To find the factorial of a number, we use the iterative method, which means we repeat a task using a loop. In this case, we multiply the numbers from 1 up to the given number to get the factorial.

Here's how we do it:

• First, we initialize the factorial value to 1.
• Then, we run a loop from 1 to the given number(n).
• In each step of the loop, we multiply the current factorial value by the loop number and update it.
• Finally, once the loop finishes, we display the result.

C++ Program to Find Factorial of a Number using Iteration

Here's a C++ program where we calculate the factorial of a given number using an iterative method:

#include <iostream>
using namespace std;

int main() {
    int n = 5;         //number to calculate the factorial
    int fa = 1;        // Variable to store factorial
    // for loop for calculation
    for (int i = 1; i <= n; ++i) {
        fa *= i;
    }

    cout << "Factorial of " << n << " using loop is: " << fa << endl;
    return 0;
}

The output of the above program shows the factorial of 5 calculated using a loop.

Factorial of 5 using loop is: 120

Time Complexity: O(n), because the loop runs n times.

Space Complexity: O(1), we use only a few variables.