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Factorial Function

07.04.2007
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        A (non-recursive) factorial function
int factorial(int x) {
 int fac = 1;
 for (int i=2; i<=x; i++) fac *= i;
 return fac;
}

Also, with this function defined, you can use two macros for calculating combinations & permutations:
#define nCr(n, r) (factorial(n) / factorial(n-r) / factorial(r))
#define nPr(n, r) (factorial(n) / factorial(n-r))