Untitled

import java.util.Scanner;

public class Main {

    public static class Stack {
        private int[] arr;
        private int top;
        private int capacity;

        public Stack(int size) {
            arr = new int[size];
            capacity = size;
            top = -1;
        }

        public void push(int x) {
            if (top == capacity - 1) {
                throw new RuntimeException("Stack Overflow");
            }
            arr[++top] = x;
        }

        public int pop() {
            if (isEmpty()) {
                throw new RuntimeException("Stack Underflow");
            }
            return arr[top--];
        }

        public boolean isEmpty() {
            return top == -1;
        }
    }

    public static int evaluatePostfix(String postfix) {
        Stack stack = new Stack(postfix.length());

        for (int i = 0; i < postfix.length(); i++) {
            char c = postfix.charAt(i);

            if (Character.isDigit(c)) {
                stack.push(c - '0');
            } else {
                int operand2 = stack.pop();
                int operand1 = stack.pop();

                switch (c) {
                    case '+':
                        stack.push(operand1 + operand2);
                        break;
                    case '-':
                        stack.push(operand1 - operand2);
                        break;
                    case '*':
                        stack.push(operand1 * operand2);
                        break;
                    case '/':
                        stack.push(operand1 / operand2);
                        break;
                    case '^':
                        stack.push((int) Math.pow(operand1, operand2));
                        break;
                    default:
                        throw new IllegalArgumentException("Unsupported operator: " + c);
                }
            }
        }
        return stack.pop();
    }

    public static void main(String[] args) throws Exception {
        System.setIn(new java.io.FileInputStream("Caculator3.txt"));
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter postfix expression (single-digit operands): ");
        String postfix = scanner.nextLine();

        int result = evaluatePostfix(postfix);
        System.out.println("Evaluation result: " + result);

        scanner.close();
    }
}