Problem using while loop with !=

Question

Hi, I'm a beginner and still learning the basics of Java!
Right now, I have a problem creating a while loop to read in two values.
This is what I have entered:
while((input != 'a') || (input != 'b'))
       Screen.out.println("Invalid Input");
       Screen.out.println("Enter 'a' or 'b' to continue");
       input = Keybd.in.readChar();
}    I'm trying to get a input from the user, either the character 'a' or 'b' to continue, where my next set of code would come in and if they did not enter the character 'a' or 'b', it would display the "Invalid Input" message.
What I can't get to happen in my while loop is that when I enter 'a' or 'b' , I still get the "Invalid Input" message etc. Even when I enter any other character in, I still get the same "Invalid Input" message. I thought the " != " mean "not equal to" and the " || " means OR. What am I doing wrong??

Answer 1

while((input != 'a') && (input != 'b'))The || operator evaluates to true if either operand is true. If you enter an 'a', (input != 'b') is true, so the code gets executed. Similarly, if you enter 'b', you obviously didn't enter an 'a', so your code gets executed.
You want to execute the code only if (input != 'a') AND (input != 'b').
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