foo.cc:12:9: error: 'string' does not name a type
   12 |         string operatorSym;
      |         ^~~~~~
foo.cc:13:9: error: 'string' does not name a type
   13 |         string infix;
      |         ^~~~~~
foo.cc:16:9: error: 'vector' does not name a type
   16 |         vector<string> postfix;
      |         ^~~~~~
foo.cc:17:9: error: 'stack' does not name a type
   17 |         stack<char> symStack;
      |         ^~~~~
foo.cc:18:9: error: 'stack' does not name a type
   18 |         stack<double> figStack;
      |         ^~~~~
foo.cc:19:9: error: 'string' does not name a type
   19 |         string stdInfix;
      |         ^~~~~~

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