求救dalao，这么写为什么不对...

#include<iostream>
#include<cstdio>
using namespace std;
struct cd {
    int x;
    int y;
};
cd zb[3];
int mh[8]={-1,-1,1,2,2,1,-1,-2},ml[8]={1,2,2,1,-1,-2,-2,-1},sum=0;
char vis[1000][1000];
void dfs(int xz,int yz)
{
    if(xz<=zb[1].x&&yz<=zb[1].y&&!vis[xz][yz])
    {
        xz++;
        if(xz==zb[1].x&&yz==zb[1].y)
        sum++;
        dfs(xz,yz);
        xz--;
        yz++;
        if(xz==zb[1].x&&yz==zb[1].y)
        sum++;
        else
        dfs(xz,yz);
        yz--;
    }
}
int main()
{
    cin>>zb[1].x>>zb[1].y;
    cin>>zb[2].x>>zb[2].y;
    for(int i=0;i<=8;i++)
    {
        vis[zb[2].x+mh[i]][zb[2].y+ml[i]]=1;
    }
    dfs(0,0);
    cout<<sum;
    return 0;
}