Thread: stacks

Hello,

I'm trying to do this stack container that reads a string and is supposed to find if the string has a balanced parentheses (opening and closing parentheses). for example

Z+ X- Y //no parentheses
Z * X / (Y+10) //Matching parenthesis
Z * ((X / Y) + D + (F-10) //Parenthesis don’t match. Missing right parenthesis
Z * (X / Y) + W + (F-10)) //Parenthesis don’t match. Missing left parenthesis

so far this is what I got

Code:

#define STACK_MAX 100

class Stack {

    private:
        int        data[STACK_MAX];
        int        size;

    public:
        Stack() {       // Constructor
            size = 0;
        }

        ~Stack() { }    // Destructor

        int top() {

            if (size == 0) {
                printf("Error: stack empty\n");
                return -1;
            }
            return data[size-1];
        }

        void push(int d) {

            if (size < STACK_MAX)
                data[size++] = d;
            else
                printf("Error: stack full\n");
        }

        void pop() {

            if (size == 0)
                printf("Error: stack empty\n");
            else
                size--;
        }
};

int
 main()
{
  


  return 0;
}

The stack looks okay.
The problem in question doesn't really require a stack though..
All you have to do is to read the expression character by character.
When you find a '(' increment a counter, and ')' to decrement.
The final count determines the result. ( 0 depicting no error).

This is where I am right now. I think this should work, but it's not doing what's supposed to do.

Code:

// A simple Integer stack, Array based
#include <algorithm>
#include <cassert>
#include <iostream>
#include <cstdlib>
#include <string>

using namespace std;

#define STACK_MAX 100

class Stack {

    private:
        int        data[STACK_MAX];
        int        size;

    public:
        Stack() {       // Constructor
            size = 0;
        }

        ~Stack() { }    // Destructor

        int top() {

            if (size == 0) {
               cout << "Error: stack empty\n";
                return -1;
            }
            return data[size-1];
        }

        void push(int d) {

            if (size < STACK_MAX)
                data[size++] = d;
            else
                cout << "Error: stack full\n";
        }

        void pop() {

            if (size == 0)
                cout << "Error: stack empty\n";
            else
                size--;
        }

        bool isEmpty() {
            if (size == 0)
                return -1;
                    else
                        return 1;
        }
};

int main()
{
const char left_p = '(';
const char right_p = ')';
bool error = false;
char ch;

Stack s;

cout << "Please enter an algebraic expression: ";
cin.get(ch);

	while (( ch != '\n')  && (!error) )
    {
		if (ch == left_p)
			 s.push(ch);


		if (ch == right_p)
			//if (s.isEmpty())
             //   error = true;
              //  else
                    s.pop();
                    cin.get(ch);
	}
		if ((!error) && s.isEmpty())
		cout<<"\nResult: This expression is valid. \n"<<endl;
            else
                cout<<"\nResult: This expression is invalid. \n"<<endl;
  return 0;
}