为什么运行的结果总是6位小数，而不是我输入的精度(c语言求π近似值)

#include <stdio.h>

#include <math.h>

int main (void)

{ double e, pi;

double funpi (double e);

printf ("Enter e:");

scanf ("%lf", &e);

pi = funpi (e);

printf ("pi = %f\n", pi);

return 0;

}

double funpi (double e)

{ int denominator, flag;

double item, sum;

flag = 1;

denominator = 1;

item = 1.0;

sum = 0;

while (fabs (item) >= e){

item = flag * 1.0 / denominator;

sum = sum + item;

flag = -flag;

denominator = denominator + 2;

}

return sum * 4;

}

printf ("pi = %.2f\n", pi);