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Thread: Help looping back to top if invalid

  1. #1
    Junior Member
    Join Date
    Jul 2014
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    Default Help looping back to top if invalid


    I am working on this java project for my homework for a beginner java class. I have it all done, with one issue. When the user inputs an invalid entry instead of just looping back up and starting over it goes down to the "Enter degrees in Fahrenheit" section. I am sure it is a simple fix. Can anyone help me with this issue? I have attached my code. Thank you for the help

    //Brett Olsen, Assignment 3, Temperature Converter
    //13 July 2014 CMIS 141
    import java.util.Scanner;
    //Welcome Screen 
    public class TemperatureConverter {
    	public static void main(String[] args){
    		System.out.print("Welcome to THE TEMPERATURE CONVERTER");
    	public static void temperatureConverter(){
    		Scanner user_input = new Scanner(System.in);
    		char selection;		
    		do {		
    			System.out.println("F/f\tfrom Fahrenheit to Celsius");
    			System.out.println("C/c\tfrom Celcius to Fahrenheit");
    			System.out.println("\nYour Option:  ");
    			selection = user_input.next().charAt(0);
    			selection = Character.toUpperCase(selection);
    	//Invalid responses		
    			boolean invalid = ((selection != 'F' && selection != 'C' && selection != 'E'));
    			if (invalid)
    				System.out.print("Invalid Selection");
    	//Selection to convert Fahrenheit to Celcius		
    			if (selection !='C' && selection !='E') {
    				System.out.println("Enter a degree in Fahrenheit:  ");
    				double fahrenheit = user_input.nextDouble();
    				System.out.println(fahrenheit + " Fahrenheit is " + ((fahrenheit -32)*(5/9.0)) + " celsius.");	
    	//Selection to convert Celcius to Fahrenheit		
    			} else if (selection!='F' && selection !='E') {
    				System.out.println("Enter a degree in Celcius:  ");
    				double celcius = user_input.nextDouble();
    				System.out.println(celcius + " Celcius is " + ((celcius * 9/5) + 32) + " Fahrenheit.");
    	//Selection to Quit program		
    			} else if (selection !='F' && selection !='C') {
    				System.out.println("Thank you have a great day!");
    		}	while (selection != 'E' && selection != 'e');

  2. #2
    Super Moderator
    Join Date
    Jun 2013
    So. Maryland, USA
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    Default Re: Help looping back to top if invalid

    Welcome to the forum! Thanks for taking the time to learn how to post code correctly. If you haven't already, please read this topic to learn other useful info for new members.

    Your program is organized to get a menu selection then execute based on the selection. I believe you're asking how to repeat the menu if the user enters an invalid menu option. A way to accomplish this is to enclose the menu and the user's response in another while or do/while statement of the form:
    boolean valid = false;
    while ( !valid )
        // present menu
        // get user input
        // if user input valid, valid = true
        // else valid = false
    If you were using multiple methods or methods beyond the main(), I would suggest presenting the menu and getting the user's input using another method, but I suspect you're not there yet.

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