Write a program in C++ to read an integer N and compute N! using for and do-while loop.

here's a C++ program to read an integer N and compute its factorial N! using both for and do-while loops.

Using for loop

#include <iostream>

using namespace std;

int main() {
    int n;
    long long fact = 1;

    // Prompt the user to enter a positive integer
    cout << "Enter a positive integer: ";
    cin >> n;

    // Compute the factorial using a for loop
    for (int i = 1; i <= n; ++i) {
        fact *= i;
    }
    cout << n << "! = " << fact << endl;
    return 0;
}

Output:

Enter a positive integer: 5
5! = 120

Using do-while loop:

#include <iostream>

using namespace std;

int main() {
    int n;
    long long fact = 1;
    int i = 1;

    // Prompt the user to enter a positive integer
    cout << "Enter a positive integer: ";
    cin >> n;

    // Compute the factorial using a do-while loop
    do {
        fact *= i;
        ++i;
    } while (i <= n);
    cout << n << "! = " << fact << endl;
    return 0;
}

Output:

Enter a positive integer: 5
5! = 120

Explanation:

• The program first declares an integer variable n to store the user input, and a long long variable fact to store the computed factorial.
• Then, the program prompts the user to enter a positive integer n using the cout object and reads the input using the cin object.
• The program uses either a for loop or a do-while loop to compute the factorial of n.
• In the for loop, the program initializes a loop variable i to 1, and iterates the loop while i is less than or equal to n. In each iteration, the program multiplies fact by i and increments i by 1.
• In the do-while loop, the program initializes i to 1 before the loop, and then multiplies fact by i and increments i by 1 inside the loop. The loop iterates while i is less than or equal to n.
• After the loop, the program uses the cout object to print the computed factorial fact using the input value n.
• Finally, the program returns 0 to indicate successful execution.