Check for balanced parentheses in an expression in C++

Suppose we have an expression. The expression has some parentheses; we have to check the parentheses are balanced or not. The order of the parentheses are (), {} and []. Suppose there are two strings. “()[(){()}]” this is valid, but “{[}]” is invalid.

The task is simple; we will use stack to do this. We should follow these steps to get the solution −

Traverse through the expression until it has exhausted
- if the current character is opening bracket like (, { or [, then push into stack
- if the current character is closing bracket like ), } or ], then pop from stack, and check whether the popped bracket is corresponding starting bracket of the current character, then it is fine, otherwise that is not balanced.
After the string is exhausted, if there are some starting bracket left into the stack, then the string is not balanced.

Example

Live Demo

#include <iostream>
#include <stack>
using namespace std;
bool isBalancedExp(string exp) {
   stack<char> stk;
   char x;
   for (int i=0; i<exp.length(); i++) {
      if (exp[i]=='('||exp[i]=='['||exp[i]=='{') {
         stk.push(exp[i]);
         continue;
      }
      if (stk.empty())
         return false;
      switch (exp[i]) {
      case ')':
         x = stk.top();
         stk.pop();
         if (x=='{' || x=='[')
            return false;
         break;
      case '}':
         x = stk.top();
         stk.pop();
         if (x=='(' || x=='[')
            return false;
         break;
      case ']':
         x = stk.top();
         stk.pop();
         if (x =='(' || x == '{')
            return false;
         break;
      }
   }
   return (stk.empty());
}
int main() {
   string expresion = "()[(){()}]";
   if (isBalancedExp(expresion))
      cout << "This is Balanced Expression";
   else
      cout << "This is Not Balanced Expression";
}