Stack_parentThesisChecker

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package parentThesisBalance;

import java.util.Scanner;
import java.util.*;

public class CheckerPT {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        try{
            Stack stack = new Stack();
            Scanner sc = new Scanner(System.in);
            System.out.println("Enter a expression");
            String exp = sc.nextLine();
            boolean flag=false;
            for (int c = 0; c < exp.length(); c++) {
                char ch = exp.charAt(c);
                if (ch == '{' || ch == '(' || ch == '[') {
                    stack.push(ch);
                }
                else if(ch=='}'||ch==')'||ch==']'){
                        if(stack.isEmpty()){
                            int found=exp.indexOf(ch);
                            System.out.println("Error at character "+ ++found);
                            System.out.println(ch+" not opened");
                        }
                        char popch=(char)stack.pop();
                        int index=exp.indexOf(popch);
                    if((ch=='}' && popch=='{')||(ch==')' && popch=='(')||(ch==']' && popch=='['))
                        flag=true;
                    else{
                        flag=false;
                        System.out.println("Expression is NOT correct");
                        System.out.println("Error at character# "+ ++index);
                        System.out.println(popch+" not closed");
                        break;
                    }
                }
            }
            if(flag)
                    System.out.println("The expression is correct");
            }catch(Exception e){
            System.out.println(e);
        }
    }

}