Question

Write a scripting interface that accepts the following commands:
   The program must run a continuous loop and not shut down after
   each operation -- that is, continuously asks for input until "exit"
   is typed.

Specification:
   Run as: java Calc
   This throws up a prompt which accepts the following syntax:
    PROMPT>> <number1> + <number2>
    PROMPT>> <number1> - <number2>
    PROMPT>> <number1> * <number2>
    PROMPT>> <number1> / <number2>
    PROMPT>> <number1> % <number2>

    example:

    PROMPT>> 3 + 6
      9
    PROMPT>> 4 - 3
      1

   Handle gracefully as many incorrect inputs as you can. For example:
         
    ex. ADDER > 3 $ 6
                         error: No such operator '$'
    
    ex. ADDER > 3 + 2 + 1
                         error: must supply only two numbers
    
    ex. ADDER > a + 2
                         error: symbol 'a' not a valid real

Answer 1

Code:

import java.util.Scanner;
public class Main
{
   public static void main(String[] args) {
  
   Scanner sc=new Scanner(System.in);
   while(true){
   System.out.print("PROMPT>>");
   String inp=sc.nextLine();
   if(inp.equals("exit")){
   System.out.println("Thank You");
   break;
   }
   else{
   String []inp1=inp.split(" ");
   if(inp1.length==3){
   if(inp1[1].equals("+" )|| inp1[1].equals("-" )|| inp1[1].equals("*" )|| inp1[1].equals("/" )|| inp1[1].equals("%")){
   float a,b;
   try{
   a=Float.parseFloat(inp1[0]);
   try{
   b=Float.parseFloat(inp1[2]);
   if(inp1[1].equals("+" )){
   System.out.println(a+b);
   }
   else if(inp1[1].equals("-" )){
   System.out.println(a-b);
   }
   else if(inp1[1].equals("*" )){
   System.out.println(a*b);
   }
   else if(inp1[1].equals("/" )){
   System.out.println(a/b);
   }
   else if(inp1[1].equals("%" )){
   System.out.println(a%b);
   }
   }
   catch(Exception e){
   System.out.println(" symbol '"+inp1[2]+"' not a valid real");
   }
   }
   catch(Exception e){
   System.out.println(" symbol '"+inp1[0]+"' not a valid real");
   }
   }
   else{
   System.out.println("No such operator '"+inp1[1]+"'");
   }
   }
   else{
   System.out.println("must supply only two numbers and an operation");
   }
   }
   }
  
   }
}

Output: