C++ Stack Implementation, checking parenthesis correctness

Question

I want to give the expression in the form of parenthesis through CIN, like: ()). then, through push & pop operation of the stack, I want the program to print me weather the given expression is BALANCED or NOT. The program works perfectly but only one issue has been found & that is when I enter like ()(, so it tells me that this expression is IMBALANCED which is fine but when I enter like () (, so then it tell me that this expression is BALANCED which is actually not balanced.

#include <iostream>

/* run this program using the console pauser or add your own getch, system("pause") or input loop */
using namespace std;

char Stack[10];
int top=-1;

void push(char ch)
{
    if(top<10)
    {
        top++;
        Stack[top] = ch;
    }
    else
        cout<<"Stack Overflow";
}

void pop()
{
    if(top > -1)
    {
        top--;
    }
    else
        cout<<"Stack Underflow";    
}
int show(){
    cout<<"It is imbalanced.";
}

int main(int argc, char** argv) 
{
    
    int a=0,b=0;
    string exp;
    cout << "Write down the parenthesis:" ;
    cin >> exp;
    bool check = true;
    
    for(int i=0; i<exp.length(); i++)
    {
        if(exp[i]== '(')
        {
            push(exp[i]);
        }
        else if(exp[i]== ')')
        {
            if(top == -1)
            {
                check = false;
                break;
            }
            else
            {
                pop();
            }
        }
    
    }
    
    for(int i=0; i<exp.length(); i++)
    {
        if(exp[i]=='('){
        ++a;
    }
    else if (exp[i]==')')
    {
        b++;
        
        }   
    }
    
    if(a>b){
        cout<<"\n\nGiven Combination is IMBALANCED";
        return 0;
    }
    
    if(check == true)
        cout<<"\n\nGiven Combination is BALANCED";
    
    else
        cout<<"\n\nGiven Combination is IMBALANCED";
    
    
    return 0;
}

Answer 1

The main comments boil down to:

• Don’t use a stack when no stack is needed.
  • And if you do use one, don’t limit it to an arbitrary fixed depth.
• Handle errors and report malformed expressions.
• Make sure you get the right input; std::getline() may be less error-prone than input tokenized using the >> operators. Just skip spaces (or whatever insignificant characters are allowed in the input).
• using namespace std; is an antipattern and a bad habit.

The basic idea: Calculate the nesting depth as you iterate over the string. It must be zero, ultimately. It must not drop below zero at any point.

#include <cstdlib>
#include <iostream>
#include <stdexcept>
#include <string>
#include <string_view>

using std::size_t;

bool correctly_parenthesized(std::string_view expression) {
  size_t depth{0};
  for (const auto character : expression) {
    switch (character) {
      case '(': ++depth; break;
      case ')': if (depth) { --depth; break; } else { return false; }
      case ' ': break;
      default: throw std::invalid_argument("invalid character");
    }
  }
  return depth == 0;
}

int main() {
  std::cout << "Write down the parentheses: ";
  std::string exp;
  std::getline(std::cin, exp);
  try {
    std::cout << (correctly_parenthesized(exp) ? "YES" : "NO") << std::endl;
  } catch (const std::exception &e) {
    std::cerr << e.what() << std::endl;
    return EXIT_FAILURE;
  }
}