Very short program that generates 1001 digits of PI
#include <stdio.h>
int d=4,r=10000,n=251,m=3335,i,k,q;main(){static int a[3340];for(;m-i;
a[i++]=2);a[m]=4;for(;n;n--){for(q=0,k=m;k;k--){a[k]=a[k]*r+q;q=a[k]/(2*k+1);
a[k]-=(2*k+1)*q;q*=k;}a[0]=a[0]*r+q;q=a[0]/r;a[0]-=q*r;printf("%04d",q);}}