Thread: Need help with simple calc java program

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.

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.

[CODE]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;
	}
 
 
}
 
[/CODE]

The error code generated is:

Exception in thread "main" java.util.InputMismatchException
at java.util.Scanner.throwFor(Unknown Source)
at java.util.Scanner.next(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at CalcJava.main(CalcJava.java:21)

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.

If you haven't yet, you probably will soon, learn try/catch logic. InputMismatchException is being thrown because your feeding an int variable something that is not a int. That goes for any kind of primitive type. If you want to fix it try

try {
// code that throws InputMismatchException
catch (InputMismatchException e) {
// do something if Exception is thrown
}