Stacks: Balanced Brackets , C#

Stacks: Balanced Brackets

//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static bool CheckString(string exp){
            bool res = true;
            char[] charArray = exp.ToCharArray();
            Stack st = new Stack();
            
            foreach(char i in charArray){
                
                string item =  i.ToString();
                if(item == "[" || item == "{" || item == "("){
                    
                        st.Push(item);
                }else if(st.Count > 0){
                
                if(item == "]"){
                    
                    if(st.Peek().ToString() == "["){
                        st.Pop();
                    }
                    else{
                        res =false;
                    }
                }
                else if(item == "}"){
                    
                    if(st.Peek().ToString() == "{"){
                        st.Pop();
                    }else{
                        res =false;
                    }                                 
                }
                else if(item == ")"){
                      
                    if(st.Peek().ToString() == "("){
                    
                        st.Pop();
                    }else{
                        res =false;
                    }
                    
                }
                }else{
                    res = false;
                }
          
            }//for

return res;
        }
        
        public static void Main(string[] args)
        {
            //Your code goes here
          int t = Convert.ToInt32(Console.ReadLine());
        for(int a0 = 0; a0 < t; a0++){
            string expression = Console.ReadLine();
           bool result =  CheckString(expression);
            if(result)
            Console.WriteLine("Yes");
            else
                Console.WriteLine("No");
        }
            
           //end code
        }
    }
}


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