recursion

[حسنين_1]

12345*6=620
i right a program and its output 620 means the facturial of 6 using recursion. i could not uderstand factorial using recursion. please help me .

[Gonbe]

The factorial of a positive integer n, n!, is 1 * 2 * 3 * ... * n for n > 0 and 1 for n = 0. Would take you about 1 second to find on google.

The simple case is when n = 0, you simply return 1.

if (n == 0)
    return 1;

Then for other cases we want to express the problem of calculating the factorial using a smaller version of the same problem so we can solve it recursively. It's easy to see that fac(n) = n * fac(n - 1).

else
    return n * fac(n - 1);

[ddanbe]

Btw. facorial of 6 = 720. 6! = 720 check it out.