BalancedParentheses.cpp

/*
  C++ Program to check for balanced parentheses in an expression using stack.
  Given an expression as string comprising of opening and closing characters
  of parentheses - (), curly braces - {} and square brackets - [], we need to 
  check whether symbols are balanced or not. 
*/
#include<iostream>
#include<stack>
#include<string>
using namespace std;
// Function to check whether two characters are opening 
// and closing of same type. 
bool ArePair(char opening,char closing)
{
	if(opening == '(' && closing == ')') return true;
	else if(opening == '{' && closing == '}') return true;
	else if(opening == '[' && closing == ']') return true;
	return false;
}
bool AreParanthesesBalanced(string exp)
{
	stack<char>  S;
	for(int i =0;i<exp.length();i++)
	{
		if(exp[i] == '(' || exp[i] == '{' || exp[i] == '[')
			S.push(exp[i]);
		else if(exp[i] == ')' || exp[i] == '}' || exp[i] == ']')
		{
			if(S.empty() || !ArePair(S.top(),exp[i]))
				return false;
			else
				S.pop();
		}
	}
	return S.empty() ? true:false;
}

int main()
{
	/*Code to test the function AreParanthesesBalanced*/
	string expression;
	cout<<"Enter an expression:  "; // input expression from STDIN/Console
	cin>>expression;
	if(AreParanthesesBalanced(expression))
		cout<<"Balanced\n";
	else
		cout<<"Not Balanced\n";
}