infix to postfix problem

jgorospe (3)
else if (stringType == 2)
{
while (topValue != "(");
{
postFix.push_back(myStack.top());
if (!myStack.empty())
{
myStack.pop();
}
}

if (!myStack.empty())
{
myStack.pop();
}
std::cout<<"leaving 2"<< std::endl;
}

I'm getting an error right before it enters the while loop. I have a feeling its because I cannot make a comparison in such manner. Any clues on how to compare an element in a string to another element?
R0mai (730)
Post a compilable *short* code which reproduces the problem. There is a ton of missing information which could be the source of your problem.
Edit : Also use [code][/code] tags.
Last edited on
jgorospe (3)
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int arithmetic_expression::inputInfix(std::string inputString)
{
    std::vector<std::string> expression = parse_string(inputString);
    std::vector<std::string>postFix;
    postFix.reserve(expression.size()+1);
    std::stack<std::string>myStack;

    //--------------------------------------------------------
    // Prints off initial Infix Expression */
    std::cout << "Infix Expression = " << std::endl;
    for(int j=0; j< expression.size(); j++)
    {
        std::cout<<expression[j] << " ";
    }
    std::cout << std::endl;
    //--------------------------------------------------------

    std::string topValue;
    int precExpression;
    int precTop;
    int stringType,checker;
    int j;

    for ( j=0;j<expression.size();j++)
    {
        stringType = type(expression[j]);

        if (stringType == 1)
        {
            myStack.push(expression[j]);

            std::cout << "Top Stack: " << myStack.top() <<std::endl;
            std::cout << "1. Progress = " << std::endl;
            for(int j=0; j< postFix.size(); j++)
            {
                std::cout<<postFix[j] << " ";
            }
            std::cout << std::endl;
        }
        else if (stringType == 2)
        {
            while (myStack.top() != "(");
            {
                postFix.push_back(myStack.top());
                if (!myStack.empty())
                {
                    myStack.pop();
                }
            }

            if (!myStack.empty())
            {
                myStack.pop();
            }

            std::cout << "Top Stack: " << myStack.top() <<std::endl;
            std::cout << "2. Progress = " << std::endl;
            for(int j=0; j< postFix.size(); j++)
            {
                std::cout<<postFix[j] << " ";
            }
            std::cout << std::endl;
        }
        else if (stringType == 3)
        {
            if (!myStack.empty())
            {
                precExpression = getPrecedence(expression[j]);
                precTop = getPrecedence(myStack.top());

                if (precTop<precExpression)
                {
                    myStack.push(expression[j]);
                }
                else
                {
                    postFix.push_back(myStack.top());
                    myStack.pop();
                    myStack.push(expression[j]);
                }
            }
            else
            {
                myStack.push(expression[j]);
            }

            std::cout << "Top Stack: " << myStack.top() <<std::endl;
            std::cout << "3. Progress = " << std::endl;
            for(int j=0; j< postFix.size(); j++)
            {
                std::cout<<postFix[j] << " ";
            }
            std::cout << std::endl;
        }
       /* else if (stringType == 4)
        {
            std::cout<<"entering 4"<< std::endl;

            postFix.push_back(expression[j]);

            std::cout<<"leaving 4"<< std::endl;
        }*/
        else if (stringType == 5)
        {
            postFix.push_back(expression[j]);

            if (!(myStack.empty()))
            {
                std::cout << "Top Stack: " << myStack.top() <<std::endl;
            }
            std::cout << "4. Progress = " << std::endl;
            for(int j=0; j< postFix.size(); j++)
            {
                std::cout<<postFix[j] << " ";
            }
            std::cout << std::endl;
        }

    }//end for

    std::cout<<"left for loop"<<std::endl;
    while (!myStack.empty())
    {
        postFix.push_back(myStack.top());
        myStack.pop();
    }

    //--------------------------------------------------------
    // Prints off initial Infix Expression */
    std::cout << "New PostFix Expression = " << std::endl;
    for(int j=0; j< postFix.size(); j++)
    {
        std::cout<<postFix[j] << " ";
    }
    std::cout << std::endl;
    //--------------------------------------------------------

    int valid = createExpressionTree(postFix);
    if (!valid) {
        topPtr = NULL;
    }

    return(valid);

}


Functions used for program

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int type(std::string type)
{
    if (type == "(")
    {
        return 1;
    }
    else if (type == ")")
    {
        return 2;
    }
    else if (type == "+" || type == "-"|| type == "*" || type == "/") //Operators
    {
        return 3;
    }
    else if (type == " ")
    {
        return 4;
    }
    else //Operands
    {
        return 5;
    }
}

int getPrecedence(std::string type)
{
    if (type == "+" || type == "-")
    {
        return 1;
    }
    else if (type == "*" || type == "/")
    {
        return 2;
    }
    else if (type == "(")
    {
        return 0;
    }
}


jgorospe (3)
Sorry it isn't exactly short
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