C :

#include<stdio.h>
#include<math.h>
int main()
{
	double pi,sum,i,sign=-1;
	for (sum=1,i=3;(1.0/i)>=pow(10.0,-6);i+=2)
	{
		sum += sign*(1.0/i);
		sign=-sign;
	}
	printf("PI=%10.8f\n",4*sum);
	getchar();
	return 0;
}

C++ :

#include <cstdio>
#include <cmath>
int main (void){
	double i,PI=0,n=0,s;
	for(i=1.0;i>0.0;i+=2){
		s=(pow(-1.0,n+2))/i;
		if(fabs(s)<pow(0.1,6.0))
				break;
		PI=PI+s;
		n++;
	}
	printf("PI=%10.8f\n",PI*4);
	return 0;
}