Using a stack to determine if an expression has balanced parentheses

Question

I am working on my last school assignment for the semester and we are being introduced to stacks for the first time but I am having an issue with my program not analyzing the expression properly. Everything executes but the program always comes out with the result that expression is unbalanced. Any clues to point me in the right direction?

//    
//  main.cpp
//  Balanced Parenthesis
#include "StringStack.h"
#include <iostream>
using namespace std;


int main ()
{
StringStack stack;
char entry;
    int parCounter = 0;
cout << "This program will accept a string and determine whether it has balanced        parenthesis.\n";
cout << "Please type a sentence to be analyzed\n";

while (cin.get (entry) && entry != '\n')
{
            stack.push(entry);

}
if (stack.isEmpty()) {
    cout << "The stack is empty./n";
}

else{
    stack.pop(entry);
    if (entry == ')') {
        parCounter++;
    }
    else if(entry == '('){
        parCounter--;
    }


}
if (parCounter > 0 || parCounter < 0){
            cout << "This expression has UNBALANCED parentheses\n";
        }
        else
        {
            cout << "This expression has BALANCED parentheses\n";

    }



return 0;
}

//  StringStack.h
//  Balanced Par

#include <iostream>
using namespace std;

#ifndef StringStack_h
#define StringStack_h


//Define our stack class and its contents
class StringStack
{
private:

    char *stackArray;
    int stackSize;
    char top;
public:
StringStack();
    ~StringStack() {delete[] stackArray;}
    void push(char);
    void pop(char &);
    bool isBalanced();
    bool isEmpty();
};

#endif

//Constructor
StringStack::StringStack()
{
    stackArray = new char[stackSize];
    top = 0;
}

//Function to determine if stack is empty.
bool StringStack::isEmpty()
{
    if (top == 0)
        return true;
    else
        return false;
}

//Function to push letters/puncuation onto the stack
void StringStack::push(char letter)
{
//if (isEmpty())
{
    top++;
    stackArray[top] = letter;
}
//else
//{
    //exit(1);
//}
}

//Function to pop letters/puncuation off the stack
void StringStack::pop(char &letter)
{
if (isEmpty())
{
    cout << "The stack is empty.\n";
    exit(1);
}
else
{
    letter = stackArray[top];
    top--;
}
}

Answer 1

You're not initialising or setting the member stackSize anywhere. This makes new char[stackSize] undefined behaviour and anything could happen.

And after you fix that, you're only inspecting the top of the stack. You need a loop around the parCount - controlling if to run until the stack is empty.