c语言编程：PI 2 = 1 + 1 3 + 1 3 2 5 + 1 3 2 5 3 7+ +

#include <stdio.h>

int main() { double pi = 1; double numerator = 1, denominator = 3; int i;

for (i = 2; i <= 1000000; i++) {
    numerator *= (i - 1);
    denominator += 2;
    pi += (numerator / denominator);
}

pi *= 2;
printf("PI / 2 = %.15f\n", pi);

return 0;

}