Java Program to evaluate simple expressions

GTU JAVA Practical 13

Write a program for calculator to accept an expression as a string in which the operands and operator are separated by zero or more spaces.
For ex: 3+4 and 3 + 4 are acceptable expressions.

				
					import java.util.Scanner;
class Practical_13 {
  public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    System.out.print("Enter Equation : ");
    String string = input.nextLine();
    String a = string.replaceAll(" ", "");

    if (a.length() < 3) {
      System.out.println(
        "Minimum 2 Opearator and 1 Opearand Required");
      System.exit(0);
    }

    int result = 0;
    int i = 0;

    while (a.charAt(i) != '+' && a.charAt(i) != '-' && a.charAt(i) != '*' && a.charAt(i) != '/') {
      i++;
    }

    switch (a.charAt(i)) {
    case '+':
      result = Integer.parseInt(a.substring(0, i)) + Integer.parseInt(a.substring(i + 1, a.length()));
      break;
    case '-':
      result = Integer.parseInt(a.substring(0, i)) - Integer.parseInt(a.substring(i + 1, a.length()));
      break;
    case '*':
      result = Integer.parseInt(a.substring(0, i)) * Integer.parseInt(a.substring(i + 1, a.length()));
      break;
    case '/':
      result = Integer.parseInt(a.substring(0, i)) / Integer.parseInt(a.substring(i + 1, a.length()));
      break;
    }

    System.out.println(a.substring(0, i) + ' ' + a.charAt(i) + ' ' + a.substring(i + 1, a.length()) +
      " = " + result);
  }
}

Output