foo.cc: In function 'int main()':
foo.cc:7:8: error: 'Pi' does not name a type
    7 |  const Pi=3.14159;
      |        ^~
foo.cc:8:12: error: 'Pi' was not declared in this scope
    8 |  cout<<20/(Pi*r*r*h/1/1000);
      |            ^~

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