c 用给定公式求π的近似值

#include<stdio.h>
int main()
{
    int i = 1,j = 1;
    double sum = 0;
    for (;i <1000000;i += 2){
        sum +=j * 1.0 / i;
        j *= -1;
    }
    printf("%lf", sum*4);
    return 0;
}