Answer to Question #292114 in Java | JSP | JSF for Jimmy

Question

Write a program to make a normal mathematics calculator.

For example:

Enter the numbers along with +, -, *, /, %, ^ symbols you want to be calculated:

5 + 4 - 7

Your calculation:

2

Remember to do using mathematics operator precedence not java operator precedence.

Answer 1

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.println("Enter the numbers along with +, -, *, /, %, ^ symbols you want to be calculated:");
        String[] operators = {"+", "-", "*", "/", "%", "^"};
        String[] equation = in.nextLine().split(" ");
        int size = equation.length;
        while (size > 1) {
            String operator = "";
            int operatorIndex = -1;
            for (int i = 0; i < size; i++) {
                for (int j = 0; j < operators.length; j++) {
                    if (equation[i].equals(operators[j])) {
                        if (operator.length() == 0 || (operators[j].equals("^") && !operator.equals("^")) ||
                                ((operators[j].equals("*") || operators[j].equals("/") || operators[j].equals("%"))
                                        && (operator.equals("+") || operator.equals("-")))) {
                            operator = equation[i];
                            operatorIndex = i;
                        }
                        break;
                    }
                }
            }
            if (operatorIndex == -1) {
                System.out.println("Wrong equation!");
                System.exit(-1);
            }
            double result = 0;
            switch (operator) {
                case "+":
                    result = Double.parseDouble(equation[operatorIndex - 1]) + Double.parseDouble(equation[operatorIndex + 1]);
                    break;
                case "-":
                    result = Double.parseDouble(equation[operatorIndex - 1]) - Double.parseDouble(equation[operatorIndex + 1]);
                    break;
                case "*":
                    result = Double.parseDouble(equation[operatorIndex - 1]) * Double.parseDouble(equation[operatorIndex + 1]);
                    break;
                case "/":
                    result = Double.parseDouble(equation[operatorIndex - 1]) / Double.parseDouble(equation[operatorIndex + 1]);
                    break;
                case "%":
                    result = Double.parseDouble(equation[operatorIndex - 1]) % Double.parseDouble(equation[operatorIndex + 1]);
                    break;
                case "^":
                    result = Math.pow(Double.parseDouble(equation[operatorIndex - 1]), Double.parseDouble(equation[operatorIndex + 1]));
                    break;
            }
            equation[operatorIndex - 1] = Double.toString(result);
            for (int i = operatorIndex + 2; i < size; i++) {
                equation[i - 2] = equation[i];
            }
            size -= 2;

        }
        System.out.println(equation[0]);
    }
}