Java Crash Course: Build a Calculator

Exercise 7: Console Calculator

For this exercise, we are going to use what we learned to create a new program that is a console calculator. It will support the basic operations, addition, subtraction, multiplication, and division. You can add whatever other functionality you would like.

The user should be able to enter a calculation like this,

4
+
5
9.0
*
2
18.0
Q

For this exercise, we will need to get user input from the console, or terminal window. That is not something I do very often so I have to look it up. Part of programming is learning how to find out how to implement something to solve a problem. For this problem we need to look up, java console input and hopefully that will get us useful results.

That lookup got some good results but the first hits were for getting a single input. We want many inputs until the user is done so we need to modify our search to java console input in a loop.

I typically go for answers from stackoverflow and the first answer led me to this implementation that uses the Scanner class.

To look up the Scanner class, search for java 11 scanner which should find the official documentation as the first hit:

// The `try` block will automatically close the input reader when
// we are done.
// Loop until the user quits.
while (true) {
// Read a line from the console.

// some other code

if ("Q".equals(line)) {
break; // exit the loop
}
}
}

Using this input code above, create a new class with a main method that implements the calculator.

Watch the video for our implementation to see if your solution is similar.

[RitwikVaidya]

Hey! Thanks for this wonderful playlist. Here's my take on the calculator implementation.
package Calculator;

import java.util.Scanner;

public class Calculator {

public static void main(String[] args) {

try (Scanner sc = new Scanner(System.in)) {

while(true) {
System.out.println("Do you want to use the calculator? (y/n)");
String answer = sc.next();
if(answer.equals("n")) {

break;
}


System.out.println("Enter first number:");
Double num1 = sc.nextDouble();
System.out.println("Enter operation:");
String operation = sc.next();
System.out.println("Enter second number:");
Double num2 = sc.nextDouble();
switch(operation) {
case "+":
System.out.println("Answer: "+(num1 + num2));
break;
case "-":
System.out.println("Answer: "+(num1 - num2));
break;
case "*":
System.out.println("Answer: "+(num1 * num2));
break;
case "/":
System.out.println("Answer: "+(num1 / num2));
break;
default:
System.out.println("Invalid operator");
}
}
} catch(Exception e) {
System.out.println("Invalid input");
}
}
}