Adding a 'While' Loop To My Program

Question

I'm working on a program that calculates the area of either a circle (C), square (S), or rectangle (R), depending on what letter the user inputs. I've tested it and it works fine; the code is below:

import java.util.Scanner;

public class TestLoops {
public static void main(String[] args) {
   Scanner input = new Scanner(System.in);

    System.out.println("What is your shape? Enter C for circle, S for " + 
            "square, R for rectangle, or X to exit: ");
    String Shape = input.nextLine();

    if (Shape.equals("C")) {
        System.out.println("What is your circle's radius?: ");
        double Radius = input.nextDouble();
        double cFormula = (3.14 * Radius * Radius);
        System.out.println("Your circle's area = " + cFormula); 
    }
    else if (Shape.equals("S")) {
        System.out.println("What is the length of your shape's sides?: ");
        double Side = input.nextDouble();
        double sFormula = (Side * Side);
        System.out.println("Your square's area = " + sFormula);           
    }
    else if (Shape.equals("R")) {
        System.out.println("What is your rectangle's height?: ");
        double Height = input.nextDouble();
        System.out.println("What is your rectangle's width?: ");
        double Width = input.nextDouble();
        double rFormula = (Height * Width);
        System.out.println("Your rectangle's area = " + rFormula);
    }

   }

  }

Now, what I want to do is add a loop to the program. For example, if the user inputs C for circle and puts in the number 22 for the radius, they'll get an answer, but I want the program to loop back to the beginning again so that it asks the user "What is your shape?...". Also, if the user types in X instead of C, S, or R, I want the program to quit, but I'm not sure how to add that in, either.

I know that I need to add a 'while' loop, but I was hoping someone could point me in the right direction, because I don't know where to insert that part of the code. Do I add the 'while' loop somewhere at the beginning of the code, after the last "if else" statement, or... Also, I'm not actually sure what to type. Should it be something like,

while (Shape == C, S, R) {
   ....?

Any help or pointers would be appreciated by any one in the coding community! I will continue to work on this code on my own as well.

Answer 1

I would go for the do, while

So, the program will always do something while the conditions that are set are being accomplished, so you want your program to look something like:

public class TestLoops {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        boolean thisB = false; /*this is the guy who will tell the loop to stop the execution when the user inserts X*/
        String shape;
        do{
            System.out.println("What is your shape? Enter C for circle, S for " +
                    "square, R for rectangle, or X to exit: ");
            shape = input.next();

            if(shape.equalsIgnoreCase("C") || shape.equalsIgnoreCase("S") || shape.equalsIgnoreCase("R")) {
                if (shape.equals("C")) {
                    System.out.println("What is your circle's radius?: ");
                    double Radius = input.nextDouble();
                    double cFormula = (3.14 * Radius * Radius);
                    System.out.println("Your circle's area = " + cFormula);
                } else if (shape.equals("S")) {
                    System.out.println("What is the length of your shape's sides?: ");
                    double Side = input.nextDouble();
                    double sFormula = (Side * Side);
                    System.out.println("Your square's area = " + sFormula);
                } else if (shape.equals("R")) {
                    System.out.println("What is your rectangle's height?: ");
                    double Height = input.nextDouble();
                    System.out.println("What is your rectangle's width?: ");
                    double Width = input.nextDouble();
                    double rFormula = (Height * Width);
                    System.out.println("Your rectangle's area = " + rFormula);
                }
            }
            else if (shape.equalsIgnoreCase("X")) thisB = true;/*or in other words: stop*/
        }
        while(!thisB);
    }

}

Things to consider:

1) Naming conventions, always start variable names with undercase using camelCase, in your example shape started with UpperCase

2) When in a while loop, use only next(), not nextLine() to pick up the values as the latter will duplicate the question in the System.out.Println.

3) The optimum way to do this is to put all your if clauses in a method and call it with the parameter from the Scanner input. Even better would be having a method per shape, as things can get hairy depending on requests