foo.cc: In function 'int main()':
foo.cc:20:30: error: 'a' was not declared in this scope
   20 |   for(int j=1;j<=n;j++) cin>>a[i][j];
      |                              ^
foo.cc:22:6: error: 'a' was not declared in this scope
   22 |   if(a[1][i]=='1'){
      |      ^

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