CODEWITHSUNDEEP
javaif-statementint
DJ87
DJ87

Reputation: 11

How to return to top of code? Maybe?

I am extremely new to programming Java and have what I'm sure is a very easy fix. I have the following code, and it works, but I was wondering how I could change it so if the user inputs something other than an int, it would loop back to the top after it gives the error message, so it would ask for a temp again. Thanks in advance.

    Scanner in = new Scanner(System.in);
    //User input of temperature
    System.out.print("Enter temperature in Celsius: ");
    if (in.hasNextInt())
    {
        int temperature = in.nextInt();
        //Now determine what state the water will be in, either ice, gas, or water.
        if (temperature >=100)
        {
            System.out.print("Gas!");
        }
        else if ((temperature <100) && (temperature >0))
        {
            System.out.print("Water!");
        }
        else if (temperature <=0)
        {
            System.out.print("Ice!");
        }
    }
    else
    {
         System.out.println("Error: Not an Integer");
         System.out.print("Please enter temperature in Celsius: ");
    }

Upvotes: 1

Views: 21520

Answers (6)

Patrick Perini
Patrick Perini

Reputation: 22633

The most simple solution to your answer is to stick your code into an infinite "run" loop.

Scanner in = new Scanner(System.in);
while (true) {
    //User input of temperature
    System.out.print("Enter temperature in Celsius: ");
    if (in.hasNextInt())
    {
        int temperature = in.nextInt();
        //Now determine what state the water will be in, either ice, gas, or water.
        if (temperature >=100)
        {
            System.out.print("Gas!");
        }
        else if ((temperature <100) && (temperature >0))
        {
            System.out.print("Water!");
        }
        else if (temperature <=0)
        {
            System.out.print("Ice!");
        }
    }
    else
    {
        System.out.println("Error: Not an Integer");
        System.out.print("Please enter temperature in Celsius: ");
    }
}

Run loops, or main loops as they're often called, provide a consistent loop that accepts user input and provides feedback. If/when you get into multi-threading/GUI programming, this is where most of your UI code goes. However, most project-based environments (Eclipse for Android apps, Xcode for iOS apps, etc.) have more complex and idiomatic run loops than while (true).

Upvotes: 0

Bela Vizer
Bela Vizer

Reputation: 2537

wrap your code with a loop, I would use while(...) for this purpose, exit condition would be an 'int' input. http://docs.oracle.com/javase/tutorial/java/nutsandbolts/while.html

To validate user input use eg. regexp something like this: userInput.matches("[-+]?\d+(\.\d+)?");

Upvotes: 0

Marc
Marc

Reputation: 257

You have to use a loop. Look here for an introduction: http://www.leepoint.net/notes-java/flow/loops/loops.html

Upvotes: 0

DejanLekic
DejanLekic

Reputation: 19797

What you are looking for is the while loop.

Upvotes: 0

user830639
user830639

Reputation:

It looks like you should look into using a while() loop. You can use a snippet like this:

Scanner scanner = new Scanner(System.in);
int input = -1; 
input = scanner.nextInt();
while (input != 0)
{
 System.out.println("Enter 0 to exit the loop.");
 input = scanner.nextInt(); //without this, you will hit a loop that never ends. 
{

Where you can add your code to convert the temperature within that loop.

Upvotes: 1

scibuff
scibuff

Reputation: 13755

move it into a method

public static void main( String args[] ){

    Scanner in = new Scanner(System.in);
    readInput( in );
}

public static void readInput( Scanner in ){

    System.out.print("Enter temperature in Celsius: "); 
    if ( in.hasNextInt() ){
        // do your stuff here
    }
    else {
        // print the errors
        readInput( in );
    }
}

Upvotes: 5

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