recursive factorial function that prints to console on it's own (C#)

March 1, 2022

This one is just to scratch an itch, and probably not even a problem worth solving on it’s own.

I’d like to write a recursive factorial function to print to the console in C#. The thing is, just out curiosity, I tried to get it to do this by only passing the function and argument. As in, I’d like to avoid having to type Console.WriteLine(Factorial(5));

It’s harder that I’d thought to just type this and get a result:

> Factorial(5);

here is the function I’ve been playing with:

int Factorial(int number)
{
    Console.Write(number != 1 ? $"{number} x " : $"{number} = \n");
    if (number <= 1) return 1; // end of the line
    number *= Factorial(number - 1); // recursive function
    Console.WriteLine(number);
    return number; // this could have been combined with line above, but more clear this way
}

the results come out like this, where instead of seeing the 2, 6 and 24. I’d just like to see the 120:

5 x 4 x 3 x 2 x 1 =
2
6
24
120

>Solution :

You could use a local function as the actual recursive part, using the outer Factorial function as a wrapper which just calls it!

int Factorial(int number)
{
    static int DoFactorial(int number) => number <= 1
        ? 1
        : number *= DoFactorial(number - 1);
        
    var answer = DoFactorial(number);
    Console.WriteLine(answer);
    
    return answer;
}