Implementation 1:

int factorial(int n){ if (n <= 0) return 1; int f = 1; do { f *= n;} while (--n); return f; } int C(int n, int k){ if (n < k) return 0; return fact(n)/(fact(k)*fact(n-k)); }

It works for n <= 12.

Implementation 2:

int C(int n, int k){ if (n < k) return 0; if (k > n/2) k = n - k; int c = 1; for (int i = 1; i <= k; i++) c = (c*(n-i+1))/i; return c; }It works for n <= 29.

The important thing to note here is that, because of the way the loop is written, the division never results in a non-integer. (Why? Think about it!)

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