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  1. #include<iostream>
  2. using namespace std;
  3. #include<string>
  4.  
  5. class Expr
  6. {
  7.     public:
  8.        virtual void print()const =0;
  9.        friend ostream& operator<<(ostream &s, const Expr &num)
  10.        {
  11.            num.print();
  12.            return s;
  13.        }  
  14. };
  15. class NumExpr : public Expr {
  16.         public:
  17.             NumExpr( string v );
  18.             string name();
  19.             virtual void print() const
  20.             {
  21.                 cout<<*this;
  22.             }
  23.  
  24.         private:
  25.             int number;
  26.             friend ostream& operator<<(ostream &s, const NumExpr &num);
  27.     };
  28.  
  29.  NumExpr::NumExpr( string n ) {
  30.         number = 10;
  31.     }
  32.     string NumExpr::name() {
  33.         return "num";
  34.     }
  35.     ostream & operator<<(ostream &s, const NumExpr &num) {
  36.         s << num.number;
  37.         return s;
  38.     }
  39. int main()
  40. {
  41.     NumExpr* numexpr = new NumExpr("hello"); 
  42.     Expr* expr = numexpr; 
  43.     cout << *expr;
  44.  
  45.  
  46.      return 0;
  47. }
Success #stdin #stdout 0.01s 2856KB
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stdin
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Standard input is empty
stdout
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10
https://ideone.com/WIz1m
language:
C++ (gcc 8.3)
created:
13 years ago
visibility:
public

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