📄 calc.cpp.html

📁 《Big C++ 》Third Edition电子书和代码全集-Part1
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<pre>  1  #include &lt;stack&gt;
  2  #include &lt;iostream&gt;
  3  #include &lt;stdexcept&gt;
  4  
  5  using namespace std;
  6  
  <font color="#0000cc">7  /**
  8    A class that implements a simple RPN calculator.
  9  */</font>
 10  class Calculator 
 11  {
 12  public:
 13     enum BinaryOperator {PLUS, MINUS, TIMES, DIVIDE};
 14  
 <font color="#0000cc">15     /**
 16        Return the current top of stack, or throw
 17        exception if there is no current value
 18        @return current top of stack
 19     */</font>
 20     int current_memory() const;
 21    
 <font color="#0000cc">22     /**
 23        Push integer value onto top of stack.
 24        @param value integer to be placed on stack
 25     */</font>
 26     void push_operand(int value);
 27  
 <font color="#0000cc">28     /**
 29        Perform indicated binary operation.
 30        @param op operation to be performed
 31     */</font>
 32     void do_operator(BinaryOperator op);
 33  
 34  private:
 35     stack&lt;int&gt; data;
 36  };
 37  
 <font color="#0000cc">38  /**
 39     A class that represents an input error.
 40  */</font>
 41  class CalcInputException : public runtime_error
 42  {
 43  public:
 44     CalcInputException(string why) : runtime_error(why) {}
 45  };
 46  
 47  int Calculator::current_memory() const
 48  {
 49     if (data.empty())
 50        throw CalcInputException("Stack Underflow");
 51     return data.top();
 52  }
 53  
 54  inline void Calculator::push_operand(int value)
 55  {
 56     data.push(value);
 57  }
 58  
 59  void Calculator::do_operator(BinaryOperator op)
 60  {
 61     int right = current_memory();
 62     data.pop();
 63     int left = current_memory();
 64     data.pop();
 65     if (op == PLUS) data.push(left + right);
 66     else if (op == MINUS) data.push(left - right);
 67     else if (op == TIMES) data.push(left * right);
 68     else if (op == DIVIDE) data.push(left / right);   
 69  }
 70  
 <font color="#0000cc">71  /**
 72     Read from input stream, performing operations.
 73     Input consists of numbers, binary operators, or commands.
 74     command p - print
 75     command q - quit 
 76     @param in input stream to be read
 77  */</font>
 78  void read(istream&amp; in) 
 79  {
 80     Calculator calc;
 81     char c;
 82  
 83     while (in &gt;&gt; c)
 84        if (isdigit(c)) 
 85        {
 86           int intval;
 87           in.putback(c);
 88           in &gt;&gt; intval;
 89           calc.push_operand(intval);
 90        }
 91        else if (c == '+') 
 92           calc.do_operator(Calculator::PLUS); 
 93        else if (c == '-') 
 94           calc.do_operator(Calculator::MINUS); 
 95        else if (c == '*') 
 96           calc.do_operator(Calculator::TIMES); 
 97        else if (c == '/') 
 98           calc.do_operator(Calculator::DIVIDE); 
 99        else if (c == 'p') 
100           cout &lt;&lt; calc.current_memory() &lt;&lt; "\n";
101        else if (c == 'q')
102           return;
103  }
104  
105  int main() 
106  {
107     try 
108     {
109        read(cin);
110     } 
111     catch (exception&amp; e) 
112     {
113        cout &lt;&lt; "caught exception " &lt;&lt; e.what() &lt;&lt; "\n";
114     }
115  }</pre>
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