Problem15
#include <iostream> #include <cmath> using namespace std; #define NUM 20 double fctr(int n) { double r = 1; for (int i = 2; i <= n; i++) { r *= i; } return r; } int main(int argc, char argv) { double ans; ans = fctr(NUM*2) / (fctr(NUM)*fctr(NUM)); printf("%lf\n", ans); return 0; }