精确度问题

#include<stdio.h>
#include<math.h>

int main() {
double n = 1.0, pi = 0.0;
int flag = 1;
while (fabs(flag / n) >= 1e-6) {
pi = pi + flag / n;
n = n + 2;
flag = -flag;
}
printf("%10.8f", pi * 4.0);
return 0;
}
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