[Iwao@fedora C61]$ g++ c61.cpp -lglut -lGL
c61.cpp: 関数 ‘void resize(int, int)’ 内:
c61.cpp:25:4: エラー: ‘::glOtrho’ has not been declared; did you mean ‘glOrtho’?
   25 |  ::glOtrho(-w/200.,w/200.,-h/200.,h/200.,-1.,1.) ;
      |    ^~~~~~~
      |    glOrtho
[Iwao@fedora C61]$ g++ c61.cpp -lglut -lGL
[Iwao@fedora C61]$ ./a.out
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