Write a program that prompts for a file name and then reads the file to check for balanced curly braces, {; parentheses, (); and square brackets, []. Use a stack to store the most recent unmatched left symbol. The program should ignore any character that is not a parenthesis, curly brace, or square bracket. Note that proper nesting is required. For instance, [a(b]c) is invalid.

Explanation:

The program is written in C++

/*

 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";

}

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