大数乘法

#include<iostream>
using namespace std;
int arr[1000], brr[1000], crr[2000];
void BigNumber(int n, int m) {
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      crr[i+j] += arr[i]*arr[j];
    }
  }
  for (int i = 0; i < m+n+3; i++) {
    if (crr[i] > 9) {
      crr[i+1] += crr[i]/10;
      crr[i] = crr[i]%10; 
    }
  }
  int i= m+n+2;
  while (i> 0 && crr[i--]==0);
  int k;
  for (k = i+1; k >= 0; k--) {
    printf("%d", crr[k]);
  }
}
int main() {
  string str1, str2;
  while (cin>>str1>>str2) {
    for (int i = str1.length()-1, j = 0; i >= 0; i--, j++) {
      arr[j] = str1[i] - '0';
    }
    for (int i = str2.length()-1, j = 0; i >= 0; i--, j++) {
      brr[j] = str2[i] - '0';
    } 
    BigNumber(str1.length(), str2.length());   
  }
}