/* pi.c */ 
#include <stdio.h>
#define asyncron
asyncron double psum( int a, int d, int n ) {
   double h=0.0;
   double pi=0.0;
   double x=0.0;
   int i=0;
   h=1.0/(double)n;
   for(i=a; i<n;i=i+d) { x=h*((double)i-0.5); pi=pi+(4.0/(1.0+x*x)); }
   pi=pi*h;
   return pi;
}
int main(int argc, char *argv[]) {
   double res1=0.0;
   double res2=0.0;
   int n=100000000;
   int step=2;
   int num;
   num=0; res1 = psum(num,step,n);
   num=1; res2 = psum(num,step,n);
   printf("pi = %f\n", res1+res2);
   return 0;
}