Need help with program

[jace5869]

Trying to figure out what I'm doing wrong in my programming assignment. I know I could more than likely clean it up and make it much more efficient, but I'm just crazy bad at programming. So, i'll post m assignment and my code and let some more experienced coders look at it.

Assignment:

1. Prompt the user for two integers.
2. Display a menu with the following options:
1. Add numbers
2. Subtract numbers
3. Quit

3. Prompt the user for a single integer that is either 1,2, or 3.
4. If the user enters an invalid selection, redisplay the menu and prompt them again. Continue this until you get a valid response (1,2,or 3). You must use a loop to do this.
5.If the user selects ‘3’ then exit the program.
6.Perform the associated operation (add or subtract) on the previously entered two integers and display the result. Return to step ‘1’ and continue in this manner until the user selects ‘3’ to exit the program.
7.Name the class CalcJava and save program as CalcJava.java
8.Submit the program using the WA3 link above.

So far I have the following code which works fine, seemingly, until I enter some non integer value for the inputs to get added/subtracted or menu choice. In which case errors get thrown out.

import java.util.Scanner;

public class CalcJava 
{
		
	public static void main(String[] args) 
	{
		
		int value1 = 0;
		int value2 = 0;
		int menuChoice = 0;
		Scanner input = new Scanner(System.in);
					
				
			
		while(menuChoice != 3)
		{
			

			System.out.printf("Please enter first number : ");
			value1 = input.nextInt();
			System.out.printf("Please enter second number : ");
			value2 = input.nextInt();
			
						
			calcMenu();
			
			menuChoice = input.nextInt();
			
			if(menuChoice % 1 != menuChoice)
				calcMenu();
				
				
			switch(menuChoice)
			{
			case 1:
				 calcAdd(value1, value2);
				break;
			case 2:
				 calcSubtract(value1, value2);
				break;
			case 3:
				System.out.println("\tGoodbye!");
				break;
			default :
				System.out.println("\tInvalid input :: Please enter a value of 1, 2, or 3");
			
			}
		};
		
			
		input.close();
		
	}

	public static void calcMenu()
	{
		System.out.println("\t\t\tWelcome to Java Calculator v1\n\n");
		System.out.println("\t1. to add two numbers.\n");
		System.out.println("\t2. to substract two numbers.\n");
		System.out.println("\t3. to exit.\n");
		System.out.printf("Please enter a selection: >");
	}
	
	public static int calcAdd(int value1, int value2)
	{
		int input1 = value1;
		int input2 = value2;
		int resultAdd = 0;
		resultAdd = input1 + input2;
		System.out.println("The sum of " + input1 + " and " + input2 + " is > " + resultAdd);
		return resultAdd;
	}
	
	public static int calcSubtract(int value1, int value2)
	{
		int input1 = value1;
		int input2 = value2;
		int resultSub = 0;
		resultSub = input1 - input2;
		System.out.println("The difference of " + input1 + " and " + input2 + " is > " + resultSub);
		return resultSub;
	}
	
	
}

The error code generated is:

Exception in thread "main" java.lang.NumberFormatException: For input string: "f"
at java.lang.NumberFormatException.forInputString(Unk nown Source)
at java.lang.Integer.parseInt(Unknown Source)
at java.lang.Integer.parseInt(Unknown Source)
at CalcJava.main(CalcJava.java:24)

Now, I'm guess using the Switch case statement is probably a bad idea for this. Also, I don't think getting input values from user before menu selection is a good idea either. I'm thinking while loop is sufficient, but probably should use if statements inside, or some type of nested loops? I'm really having a hard time with this, and the book we use (Java Programming: Joyce Farrell: 9781111529444: Amazon.com: Books)

Any help or guidance is appreciated.

[DrummondAW]

Look into learning how to use Try and Catch effectively to capture this error and respond accordingly. If your code does not have a way to handle errors it will crash.

[SJF]

OK. So that exception is saying that Scanner.nextInt() is making a call to Integer.parseInt(String s)... and that is failing because "f" is not an integer.... go figure...

If you haven't learned about try/catch blocks yet.... well it's never too soon to learn, but your instructor may not be expecting them, so....
Scanner does have a nifty .hasNextInt() which does this for you!

            	System.out.printf("Please enter first number : ");
            	while(!input.hasNextInt()){      //While Scanner does not have in int waiting for it, prompt the user to stop messing around.
            		System.out.printf("That's not a number!  Please enter first number : ");
                	input.nextLine();            //This just grabs the current line... which isn't an int!  (and chucks it)
                }
                value1 = input.nextInt();

etc.

[jace5869]

Thanks for the help!

I had sent an e-mail to my professor about the issue as well, and since we haven't covered handling exceptions - it's not required yet. I will take a look at seeing how I can fit the has.NextInt into my code. I really do appreciate the help.