10. Adding items to a map

• Use operator[ ] to access items

  
      map< string, int > agemap;
      string name = "fred";
      agemap[ name ] = 45;      // "fred" --> 45
      int age = agemap[ name ];
      ++agemap[ name ];         // now "fred" --> 46
  
  

• Note: use of operator[ ] will put items in if they aren't there!

• Generally, this is very useful, occasionally a pain.

  
      map< string, int > visit_count;
      string name = "fred";
      ++visit_count[ name ]; // Works fine!!