（3）D - 子矩阵求和

#include<stdio.h>
int main()
{
  int i, j,m,n;
  int a[500][500];
  scanf("%d%d", &m, &n);//输入m x n数组
  for (i = 1; i <= m; i++)
    for (j = 1; j <= n; j++)
      scanf("%d", &a[i][j]);
  int q;
  scanf("%d", &q);
  while (q--)
  {
    int x1, x2, x3, x4;
    int sum = 0;
    scanf("%d%d%d%d", &x1, &x2, &x3, &x4);
    for(i=x1;i<=x2;i++)
      for (j = x3; j <= x4; j++)
      {
        sum = sum + a[i][j];
      }
    printf("%d\n", sum);
  }
  return 0;
}