built in factorial function in c++

The factorial function in C++ is not built-in, but you can write your own implementation. Here is an example of how you can implement the factorial function in C++:

#include <iostream>

int factorial(int n) {
    if (n == 0 || n == 1) {
        return 1;
    } else {
        return n * factorial(n - 1);
    }
}

int main() {
    int num = 5;
    int result = factorial(num);
    std::cout << "The factorial of " << num << " is " << result << std::endl;
    return 0;
}

Explanation: - The factorial function takes an integer n as input and returns the factorial of n. - The base case of the factorial function is when n is 0 or 1, in which case the factorial is 1. - If n is greater than 1, the function recursively calls itself with n-1 and multiplies the result by n. - In the main function, we declare a variable num and assign it a value of 5. - We then call the factorial function with num as the argument and store the result in the result variable. - Finally, we print the result to the console.

Please note that the factorial function implemented here assumes that the input n is a non-negative integer.