C++ Program

The simple C++ program that calculates the factorial of a number entered by the user using a for loop:

#include <iostream>

int main() {
    int num;
    long long factorial = 1;

    std::cout << "Enter a positive integer: ";
    std::cin >> num;

    if (num < 0) {
        std::cout << "Factorial is not defined for negative numbers." << std::endl;
    } else {
        for (int i = 1; i <= num; ++i) {
            factorial *= i;
        }
        std::cout << "Factorial of " << num << " is " << factorial << std::endl;
    }

    return 0;
}

This program does the following:

1. Includes the <iostream> header for input and output operations.
2. Defines the main function as the entry point of the program.
3. Declares an integer variable num to store the user’s input and a long long variable factorial to store the result.
4. Prompts the user to enter a positive integer.
5. Reads the user’s input into the num variable using cin.
6. Checks if the entered number is negative. If it’s negative, it displays a message that factorial is not defined for negative numbers.
7. If the number is non-negative, it calculates the factorial using a for loop and displays the result.

Compile and run this program, and it will calculate the factorial of the input number.