foo.cc: In function ‘void Topo_dfs(int)’:
foo.cc:64:9: warning: unused variable ‘i’ [-Wunused-variable]
   64 |     int i, j, x, y;
      |         ^
foo.cc:64:12: warning: unused variable ‘j’ [-Wunused-variable]
   64 |     int i, j, x, y;
      |            ^
foo.cc: In function ‘int main()’:
foo.cc:118:5: warning: this ‘for’ clause does not guard... [-Wmisleading-indentation]
  118 |     for (l=0; l<26; l++)
      |     ^~~
foo.cc:133:9: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the ‘for’
  133 |         Topo_dfs( 0 );
      |         ^~~~~~~~
foo.cc:89:18: warning: unused variable ‘x’ [-Wunused-variable]
   89 |     int i, j, l, x, y, z;
      |                  ^
foo.cc:89:21: warning: unused variable ‘y’ [-Wunused-variable]
   89 |     int i, j, l, x, y, z;
      |                     ^