/in/foo.cc: In function 'int main()':
/in/foo.cc:24:16: warning: statement has no effect [-Wunused-value]
      {a[i][j+1]==0;
       ~~~~~~~~~^~~
/in/foo.cc:25:13: warning: statement has no effect [-Wunused-value]
    a[i][j-1]==0;
    ~~~~~~~~~^~~
/in/foo.cc:26:13: warning: statement has no effect [-Wunused-value]
    a[i+1][j]==0;
    ~~~~~~~~~^~~
/in/foo.cc:27:13: warning: statement has no effect [-Wunused-value]
    a[i-1][j]==0;
    ~~~~~~~~~^~~
/in/foo.cc:28:11: warning: statement has no effect [-Wunused-value]
    a[i][j]==0;
    ~~~~~~~^~~
/in/foo.cc:33:6: error: 'i' was not declared in this scope
  for(i=1;i<=n;i++)
      ^
/in/foo.cc:34:6: error: 'j' was not declared in this scope
  for(j=1;j<=n;j++)
      ^
/in/foo.cc:36:6: error: 'b' was not declared in this scope
   if(b[i][j])
      ^