明天要考级了，还是个菜鸟(;´༎ຶД༎ຶ`)

有大佬帮我看一下吗！！！

#include<bits/stdc++.h>
using namespace std;
int t;
char a[105][105];
char b[5][5]={'0','0','0','0'
            ,'0','1','1','0'
            ,'0','1','1','0'
            ,'0','0','0','0'};
int main() {
	cin >> t;
	while(t--) {
		int n,m;
		cin >> n >> m;
		for(int i = 1;i <= n;i++) {
			for(int j = 1;j <= m;j++) {
				cin >> a[i][j];
			}
		}
		int flag=0;
		for(int i = 0;i <= n-4;i++) {
			for(int j =0;j <= m-4;j++) {
				for(int i1=0;i1 < 4;i1++) {
					for(int j1=0;j1 < 4;j1++) {
						if(a[i1][j1]!=a[i][j]) {
	   						flag=1;
						}
					}
				}
			}
		}
		if(flag == 0)
			cout << "Yes" << endl;
		else
			cout << "No" << endl;
	}
	return 0;
}