看清题目!4都忘记乘了...以及函数fabsl
#include <stdio.h>
#include <math.h>
int main()
{
long double pi = 0;
int j, flag = 1;
for(j=1; ;j+=2)
{
long double num = 1.0/j*flag;
if(fabsl(num) < pow(10, -6))
break;
pi += num;
flag = -flag;
}
printf("%.6Lf\n", pi*4);

return 0;
}