tell me why

#include<iostream>
#include<cstdio>
#include<cstring>
#include<quece>
using namespace std;
int a[31][31];
int main()
{
    int n;
    int ans1,ans2,ans3,ans4;
    cin>>n;
    for(int i=1;i<=n;++i)
     for(int j=1;j<=n;++j)
          cin>>a[i][j];
    for(int i=1;i<=n;++i)
     for(int j=1;j<=n;++j)
     {
         ans1=0,ans2=0,ans3=0,ans4=0;
         if(a[i][j]==0)
         {
             for(int z=1;z<=j-1;++z)if(a[i][z]==1)ans1=1;
             for(int x=j+1;x<=n;++x)if(a[i][x]==1)ans2=1;
             for(int c=1;c<=i-1;++c)if(a[c][j]==1)ans3=1;
             for(int v=i+1;v<=n;++v)if(a[v][j]==1)ans4=1;
         }
         if(ans1+ans2+ans3+ans4==4)a[i][j]=2;
     for(int i=1;i<=n;++i)
     {
        for(int j=1;j<=n;++j)
          cout<<a[i][j]<<" ";
        cout<<endl;
     }
    return 0;
}