converting infix to postfix

This is a discussion on converting infix to postfix within the C++ Programming forums, part of the General Programming Boards category; I have an assignment to write a program that converts an infix mathematical expression into a postfix mathematical expression using ...

  1. #1
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    Join Date
    Feb 2008
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    Question converting infix to postfix

    I have an assignment to write a program that converts an infix mathematical expression into a postfix mathematical expression using a template class and a stack. I am inexperienced at using both and have been learning as I go along. What I have written so far works in my head but I cannot seem to get it to compile.
    Code:
    #include<iostream>
    #include<iomanip>
    #include<fstream>
    #include<cmath>
    #include "header.h"
    using namespace std;
    int main()
    {
    	char infix[50];
    	char postfix[50];
    	int k=0;
    	int j=0;
    	int token;
    	for(int h=0; h<50; h++)
    	{
    		infix[h] = '#';
    		postfix[h] = '#';
    	}
    	cout << "enter infix expression: ";
    	cin.getline(infix, '\n');
    	StackType<char>  Operator;
    	char temp;
    	token = infix[0];
    	while(token != '=')
    	{
    		if(checkOperand(token))
    		{
    			postfix[k] = token;
    			k++;
    		}
    		if(token == ')')
    		{	
    			temp = Operator.top();
    			Operator.pop();
    			while(temp != '(')
    			{
    				postfix[k] = temp;
    				k++;
    				Operator.pop();
    			}
    		}
    		if(checkOperator(token))
    		{
    			if(tokenPrecedence(token)>=tokenPrecedence(Operator.top())||token=='(')
    			{
    				Operator.push(token);
    			}
    			else
    			{
    				temp = Operator.top();
    				Operator.pop();
    				postfix[k] = temp;
    				k++;
    				Operator.push(token);
    			}
    		}
    		j++;
    		token = infix[j];	
    	}
    	while(Operator.isEmpty()==false)
    	{	
    		temp = Operator.top();
    		postfix[k] = temp;
    		k++;
    		Operator.pop();
    	}
    	postfix[k] = token;
    	return 0;
    }
    bool checkOperand(int token)
    {
    	switch(token)
    	{
    	case 1:
    	case 2:
    	case 3:
    	case 4:
    	case 5:
    	case 6:
    	case 7:
    	case 8:
    	case 9:
    	case 0:
    		return true;
    	default:
    		return false;
    	}
    }
    bool checkOperator(int token)
    {
    	switch(token)
    	{
    	case '+':
    	case '-':
    	case '/':
    	case '*':
    		return true;
    	default: 
    		return false;
    		
    	}
    }
    int tokenPrecedence(int token)
    {
    	int prec=0;
    	switch(token)
    	{
    	case '*':
    	case '/':
    		prec = 1;
    		break;
    	case '+':
    	case '-':
    		prec = -1;
    		break;
    	default:
    		break;
    	}
    }
    And here is the implimentation file for the stack:
    Code:
    //Michael Bradford
    //CPSCI 131
    #include<iostream>
    #include<iomanip>
    using namespace std;
    template <class plate>
    StackType<plate>::StackType()
    {
    	top = -1; //initializing position of top value to -1
    	MaxSize=50; //initializing the maximum size of the stack to 50
    	size=0; //size of the stack
    	the_array = new int[size]; //initializing the stack to the size of 0
    }
    template <class plate>
    StackType<plate>::~StackType()
    {
    	delete [] the_array;
    }
    template <class plate>
    bool StackType<plate>::isEmpty()
    {
    	bool truthvalue=false; //true or false if empty
    	if(top==-1) //if the stack is empty than truthvalue is true
    		truthvalue = true;
    	return truthvalue;
    }
    template <class plate>
    bool StackType<plate>::isFull()
    {
    	bool truthvalue=false; //true or false if full
    	if(top==(MaxSize-1)) //if the stack us full than truthvalue is true
    		truthvalue = true;
    	return truthvalue;
    }
    template <class plate>
    void StackType<plate>::push(int newItem)
    {
    	try
    	{
    		if(isFull()) //if stack is full than throw an error
    			throw newItem;
    		top++; //if stack is not full than make room
    		the_array[top] = newItem; //add newItem to the top of the stack
    	}
    	catch(int e)
    	{
    		cout << "error! stack is full!"; //error if the stack is full
    	}
    }
    template <class plate>
    void StackType<plate>::pop()
    {
    	try
    	{
    		if(isEmpty()) //if stack is empty than throw an error
    			throw isEmpty();
    		top--;//if stack is not empty than remove item from top of stack
    	}
    	catch(bool e)
    	{
    		cout << "error! stack is empty!"; //error if the stack is empty
    	}
    }
    template <class plate>
    int StackType<plate>::top()
    {
    	try
    	{
    		if(isEmpty()) //if the stack is empty than throw an error
    			throw isEmpty();
    		return the_array[Top]; //if the stack is not empty than return the top value
    	}
    	catch(bool e)
    	{
    		cout << "error! stack is empty!"; //error if the stack is empty
    	}
    }
    The errors I get are

    implementation.cpp: In constructor ‘StackType<plate>::StackType() [with plate = char]’:
    Assignment4.cpp:21: instantiated from here
    implementation.cpp:9: error: invalid use of member (did you forget the ‘&’ ?)
    implementation.cpp:12: error: cannot convert ‘int*’ to ‘char*’ in assignment
    implementation.cpp: In member function ‘void StackType<plate>::pop() [with plate = char]’:
    Assignment4.cpp:34: instantiated from here
    implementation.cpp:57: error: no post-decrement operator for type
    implementation.cpp: In member function ‘void StackType<plate>::push(int) [with plate = char]’:
    Assignment4.cpp:46: instantiated from here
    implementation.cpp:42: error: no post-increment operator for type
    implementation.cpp:43: error: invalid use of member (did you forget the ‘&’ ?)
    implementation.cpp:43: error: array subscript is not an integer
    implementation.cpp: In member function ‘bool StackType<plate>::isEmpty() [with plate = char]’:
    Assignment4.cpp:60: instantiated from here
    implementation.cpp:23: error: invalid use of member (did you forget the ‘&’ ?)
    implementation.cpp: In member function ‘bool StackType<plate>::isFull() [with plate = char]’:
    implementation.cpp:40: instantiated from ‘void StackType<plate>::push(int) [with plate = char]’
    Assignment4.cpp:46: instantiated from here
    implementation.cpp:31: error: invalid use of member (did you forget the ‘&’ ?)

    Any help would be greatly appreciated, thanks.

  2. #2
    and the Hat of Guessing tabstop's Avatar
    Join Date
    Nov 2007
    Posts
    14,185
    Looking at the constructor,
    Code:
    StackType<plate>::StackType()
    {
    	top = -1; //initializing position of top value to -1
    	MaxSize=50; //initializing the maximum size of the stack to 50
    	size=0; //size of the stack
    	the_array = new int[size]; //initializing the stack to the size of 0
    }
    Shouldn't the_array be an array of type plate, rather than of type int? (And it should have size MaxSize, not size.)

    Edit: Also, from the errors, top appears not to be an int variable.
    Last edited by tabstop; 10-24-2008 at 08:32 AM.

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