Sum of submatrix

Enter a  n That's ok  m  The integer matrix of columns , Input again  q A asked , Each query contains four integers  x1,y1,x2,y2 Represents the upper left and lower right coordinates of a submatrix .

For each query, the sum of all numbers in the output submatrix .

 

  understand ：

  The code description ：

  Code ：

#include<iostream>
using namespace std;
const int N=1010;
int n,m,q;
int a[N][N],s[N][N];
int main()
{
    cin>>n>>m>>q;
    for(int i=1;i<=n;i++)
    {
       
        for(int j=1;j<=m;j++)
        {
            cin>>a[i][j];
            s[i][j]=s[i-1][j]+s[i][j-1]-s[i-1][j-1]+a[i][j];
        }
    }
    
    
    
    
    
    // check 
    int x1,y1,x2,y2;
    for(int i=0;i<q;i++)
    {
    cin>>x1>>y1>>x2>>y2;
    cout<<(s[x2][y2]-s[x2][y1-1]-s[x1-1][y2]+s[x1-1][y1-1])<<endl;
    
    }
}