Thread: Do while loop skipping method 3 times

Hello, I started learning java two days ago and I am well on my way on completing my first calculator.

                do
		{
		System.out.println("Indicate the operation: ");
		input.CheckInputType(symbol[count]); 
		}
		while(symbol[count] != '*');

This code will print "Indicate the operation: " three times before asking for input again IF the symbol isn't *.

Here is the CheckInputType method in case it is needed:

EDIT: Apparently, I cannot add two code tags as of now, I'll blend it with the code up there.
EDIT: That doesn't work either.. I'll just make another post with the second method.

--- Update ---

The method:

package calcPackage;
 
import java.io.IOException;
 
public class TypeCheck2 extends TypeCheck
{
	@SuppressWarnings("static-access")
	public boolean CheckInputType(char character)
	{
		try
		{
			character = (char) System.in.read();
		} catch (IOException e)
		{
			System.out.println("Invalid input!");
			return false;
		}
        super.symbol[super.count] = character; //The only way I could think of to pass the input back from the method
		return true;
	}
}

This has to do with how the character is read in. Once you read the first character, the buffer still has some sort of data in it. You have to clear the buffer once you get your character.

Indicate the operation: 
-
45
Indicate the operation: 
13
Indicate the operation: 
10
Indicate the operation:

Why does it take the input three times when I only indicated one symbol? Why do the values change?

Nvm. How do I clear the buffer?

Show us the code that asks the user to "Indicate the operation:" and accepts/processes the input.

I believe I have already supplied the necessary information, but.. this may help clarify:

public static void insertSymbol()
	{
		TypeCheck2 input = new TypeCheck2();
 
		do
		{
		System.out.println("Indicate the operation: ");
		input.CheckInputType(symbol[count]); 
		}
		while(symbol[count] != '*');
 
		if ((symbol[count] == '=') && (count != 0)) 
		{
			seeResult = true;
		}
	}

So where do the '45', '13' and '10' come from? What print statement is outputting those values to the terminal?

Originally Posted by GregBrannon

So where do the '45', '13' and '10' come from? What print statement is outputting those values to the terminal?

package calcPackage;
 
import java.io.IOException;
 
public class TypeCheck2 extends TypeCheck
{
	@SuppressWarnings("static-access")
	public boolean CheckInputType(char character)
	{
		try
		{
			int tempCharacter;
			tempCharacter =  System.in.read();
			System.out.println(tempCharacter);
			character = (char)tempCharacter;
 
 
		} catch (IOException e)
		{
			System.out.println("Invalid input!");
			return false;
		}
        super.symbol[super.count] = character; //The only way I could think of to pass the input back from the method
		return true;
	}
}

I would suggest using a Scanner to abstract yourself from the System.in class. It's a bit easier to deal with.

Originally Posted by Parranoia

I would suggest using a Scanner to abstract yourself from the System.in class. It's a bit easier to deal with.

That was my plan, however the Scanner has no sc.readChar();

Bump. I will post the full program if that is what it takes to find a solution.

Originally Posted by Norm

Make a small, simple program that compiles, executes and shows the problem. Copy the full contents of the console window from when you execute the test program and paste it here. Add some comments saying what is wrong.

package simpleProgram;
 
import java.io.IOException;
 
public class Calculator
{
 
	public static void main(String[] args)
	{
 
		char symbol = 0;
		do
		{
			try
			{
				System.out.println("Please indicate the operation:");
				symbol = (char) System.in.read();
				//System.in.skip(200); // If I ask it to skip anything else, then it doesn't sh//ow 'Please indi...' three times.
				//if it is skip(1) and I enter one symbol, it will print 'Please indi...' twice.
				//so the junk I receive is always two characters aside from what is entered.
				//How do I make it read only 1 char, and discard anything else regardless of th//e amount of chars entered?
 
			} catch (IOException e)
			{
				System.out.println("Invalid input!");
 
			}
		} while (symbol != '*'); //if '((symbol != '*') || (symbol != '/'));' then no matter what I
// enter,
		//it's false
		//if just '(symbol != '*')' then it works as intended, however I need 4 dif. symbols.
		System.out.println("Operation symbol received successfully!");
 
	}
 
}

[COLOR="Silver"]

--- Update ---

 Please indicate the operation:
*
Operation symbol received successfully!

Please indicate the operation:
-
Please indicate the operation:
Please indicate the operation:
Please indicate the operation:
*
Operation symbol received successfully!

Originally Posted by Norm

What char is read by the read() method? When is the condition in the while() statement true?
Add a println() statement that prints out what is in the symbol variable so you can see what is read and then understand what the program is doing.


The read() method is a very low level method that returns what the OS sends to the program. If you are going to use it, you must understand what the OS can send and write code to handle it.

When I execute the code I get this in the command prompt window:

I added a println just under the
symbol = (char)System.in.read();

Please indicate the operation:
/
Symbol is: /
Please indicate the operation:
Symbol is: 
 
Please indicate the operation:
Symbol is: 
 
Please indicate the operation:
*
Symbol is: *
Operation symbol received successfully!

Any insights? .. Here's another one where I print out the result before casting to char:

Please indicate the operation:
/
Symbol is: 47
Please indicate the operation:
Symbol is: 13
Please indicate the operation:
Symbol is: 10
Please indicate the operation:
*
Symbol is: 42
Operation symbol received successfully!

If it's a such a low level method, then what would be a better alternative where I can check if the input entered is indeed a char?
I do realize that what is entered may as well be an int and just get converted into a char.. In any case, I just want it to work as intended. I do not know any other way to handle the input aside from System.in and Scanner.

So it's alright to dismiss the System.in method as unneeded or unreliable?

Aside from that.. The renewed version still does funky stuff.

package simpleProgram;
 
import java.io.IOException;
import java.util.Scanner;
 
public class Calculator
{
 
 
	public static void main(String[] args) //throws IOException
	{
 
		String symbol = null;
		Scanner sc = new Scanner(System.in);
		do
		{
			System.out.println("Please indicate the operation:");
			symbol =  sc.next();
			System.out.println("Symbol is: " + symbol);
		} while ((symbol.charAt(0) != '*') && symbol.length() != 1); 
		System.out.println("Operation symbol received successfully!");
 
	}
 
}

Please indicate the operation:
///////////
Symbol is: ///////////
Operation symbol received successfully!

I updated the code above. I made a mistake, however it still doesn't do what I wanted.

The program printed out this:

Please indicate the operation:
*****
Symbol is: *****
Operation symbol received successfully!

However I want it to print stuff like this:

Please indicate the operation:
///////////
Symbol is: ///////////
Please indicate the operation:
*****
Symbol is: *****
Please indicate the operation:
/
Symbol is: /
Please indicate the operation:
*
Symbol is *
Operation symbol received successfully!

I want the do {} while to loop until I get the input I desire. In this case, a symbol '*' which is of length 1.

I want it to exit the loop when I receive the above-mentioned symbol.

You repeatedly tell me to look at the conditions, hence I am blind to my mistake and it is something incredibly silly and obvious.
I realized that my human logic did not work here.

I want the loop to exit when the symbol is * AND the string length is 1, however I noticed that it will keep looping only while both of the conditions are not true. I want it to keep looping while........... either of the statements are not true. Yes, that should do the trick.. Incredibly silly of me but it takes me a while. It's kind of like thinking backwards right now.

Thank you for your patience, the program works fine now.