2-7近似计算pi

#include <stdio.h>
int main()
{
double pi=0,i=1,d=0.0001;
int j=1,k=1,fo=0;
for(fo=0;fo<6;fo++)
{
printf("d=%g\t\t",d);
while(i>d)
{
i=1.0/j;
pi+=i*k;
j+=2;
k=-k;
}
printf("pi=%lf\n",pi*4.0);
d=d/10.0;
}
return 0;
}