Pi

#include "stdio.h"

void pi(int* p, int n) {
  int N=(10*n/3+1);
  int rest[N];
  int z[N];
  int sum[N];

  for(int i=0;i<N;i++) {
    rest[i] = 2;
  }

  z[N-1] = 0;
  for(int i=0; i<n; i++) {
    for(int j=N-1; j>0; j--) {
      int k = (j<<1)+1;
      sum[j] = 10 * rest[j] + z[j];
      rest[j] = sum[j] % k;
      z[j-1] = sum[j]/k*j;
    }
    sum[0] = rest[0] * 10 + z[0];
    rest[0] = sum[0] % 10;
    p[i] = sum[0]/10;
  }

  for(int i=n-1; i>0; i--) {
    if(p[i] == 10) {
      p[i-1] = (p[i-1] + 1) % 10;
      p[i] = 0;
    }
  }
}

void printArray(int* A, int n) {
  for(int i=0; i<n; i++) {
    printf("%d",A[i]);
  }
  printf("\n");
}

int main () {
  int n=100000;
  int p[n];
  pi(p,n);
  printArray(p,n);
}