Factorial

Part of TutorialIntermediate

Description

Shows how a factorial function can be written using a "for" loop.

Example

import std.stdio;

uint factorial(int a) {
    /*
      A factorial is a mathematical concept that is typically denoted with a "!".
      Example:
      4! = 4 * 3 * 2 * 1 = 24
    */

    if(a == 0) return 1;

    uint b = 1;
    for(int i = 1; i <= a; i++)
        b *= i;
    return b;
}

unittest
{
    /* Compile with the "-unittest" option to run these unittests. */

    writefln("Attempting unittests...");
    assert(factorial(0) == 1);
    assert(factorial(1) == 1);
    assert(factorial(2) == 2);
    assert(factorial(3) == 6);
    assert(factorial(4) == 24);
    writefln("unittests successful...");
}


void main()
{
    writefln("factorial(0): %d", factorial(0));
    writefln("factorial(1): %d", factorial(1));
    writefln("factorial(2): %d", factorial(2));
    writefln("factorial(3): %d", factorial(3));
    writefln("factorial(4): %d", factorial(4));
}