怎样用c语言编写求PI的近似值?

#include
#include
main()
{
double t,pi;
long int n,s;
t=1.0;
n=1;
s=1;
pi=0.0;
while (fabs(t)>=1e-6)
{
pi=pi+t;
n=n+2;
s=-s;
t=(float)(s)/(float)(n);
}
pi=pi*4;
printf(" pi=%lf\n",pi);
}