4-1

#include<stdio.h>
#include<math.h>
int main(void)
{
int denominator,flag;
double item,pi;

flag=1;
denominator=1;
item=1.0;
pi=0;

while(fabs(item)>=0.0001){
item=flag*1.0/denominator;
pi=pi+item;
flag=-flag;
denominator=denominator+2;
}

pi=pi*4;
printf("pi=%.4f\n",pi);

return 0;

}