postfix.cpp

data+structures+using+c的源码

// Postfix Calculator  

#include <iostream>
#include <iomanip>
#include <fstream>
#include "mystack.h"

using namespace std;

void evaluate(ofstream& out,stackType<double>& stack,
			  char& ch,bool& expressionOk);
void discard(ifstream& in, ofstream& out, char& ch);

int main()
{
	double num, result;  
	bool expressionOk;
	char ch;
	stackType<double> stack(100);
	ifstream infile;
	ofstream outfile;
	
	infile.open("a:\\Ch7_RpnData.txt");

	if(!infile)
	{
		cerr<<"Cannot open the input file. "
			<<"Program terminates!"<<endl;
		return 1;
	}

	outfile.open("a:\\ch7_RpnOutput.txt");

	outfile<<fixed<<showpoint;
	outfile<<setprecision(2); 

	infile>>ch;
	while(infile)
	{
		stack.initializeStack();
		expressionOk = true;
		outfile<<ch;

		while(ch != '=')
		{
			switch(ch)
  			{
			case '#': infile>>num;
		 			  outfile<<num<<" ";
			  		  if(!stack.isFullStack())
						 stack.push(num);
					  else
					  {
						  cerr<<"Stack overflow. "
				              <<"Program terminates!"<<endl;
						  return 1;
					  }

					  break;
			default: evaluate(outfile, stack, ch, expressionOk);

			}//end switch

			if(expressionOk) //if no error
			{
				infile>>ch;
				outfile<<ch;

				if(ch != '#')
				   outfile<<" ";
			}
			else
			    discard(infile,outfile,ch);
		}//end while (!= '=')

		if(expressionOk) //if no error, print the result
		{
			if(!stack.isEmptyStack())
			{
				result = stack.top();
  				stack.pop();

				if(stack.isEmptyStack())
					outfile<<result<<endl;
				else
	  				outfile<<" (Error: Too many operands)"<<endl;
			}//end if
			else
				outfile<<" (Error in the expression)"<<endl;
		}
		else
			outfile<<" (Error in the expression)"<<endl;

 		outfile<<"_________________________________"<<endl<<endl;

		infile>>ch; //begin processing the next expression
	}//end while 

	infile.close();
	outfile.close();

	return 0;

}//end main

void evaluate(ofstream& out, stackType<double>& stack,
              char& ch, bool& expressionOk)
{
    double op1, op2;

    if(stack.isEmptyStack())
    {
       out<<" (Not enough operands)";
       expressionOk = false;
    }
    else
    {
       op2 = stack.top();
       stack.pop();

       if(stack.isEmptyStack())
       {
          out<<" (Not enough operands)";
          expressionOk = false;
       }
       else
       {
          op1 = stack.top();
          stack.pop();

          switch(ch)
          {
          case '+': stack.push(op1 + op2);
                    break;
          case '-': stack.push(op1 - op2);
                    break;
          case '*': stack.push(op1 * op2);
                    break;
          case '/': if(op2 != 0)
                       stack.push(op1 / op2);
                    else
                    {
                       out<<" (Division by 0)";
                       expressionOk = false;
                    }
                    break;
          default:  out<<" (Illegal operator)";
                    expressionOk = false;
          }//end switch
       }//end else
    }//end else
}//end evaluate



void discard(ifstream& in, ofstream& out, char& ch)
{
   while(ch != '=')
   {
	     in.get(ch);
	     out<<ch;
   }
}//end discard