Homework Question...

Question

I'm having problem with my do while loop in a self constructed method. When I attempt to use a != for the test it just reruns the loop.
Written like this the loop just continues :
public static char displaymenu()
     char y, ch;
     String x;
     Scanner kb = new Scanner(System.in);
do {
     System.out.println("Please select one of the following: ");
     System.out.println("F - to convert Fahrenheit to Celsius ");
     System.out.println("C - to convert Celsisu to Fahrenheit ");
     System.out.println("Q - to Quit. ");
     System.out.print("Choice: ");
x =kb.next();
ch = x.charAt(0);
y = Character.toUpperCase(ch);
} while ( y !='Q'|| y!='F'|| y!='C');
return y;
Written like this the loop works:
public static char displaymenu()
     char y, ch;
     String x;
     Scanner kb = new Scanner(System.in);
do {
     System.out.println("Please select one of the following: ");
     System.out.println("F - to convert Fahrenheit to Celsius ");
     System.out.println("C - to convert Celsisu to Fahrenheit ");
     System.out.println("Q - to Quit. ");
     System.out.print("Choice: ");
x =kb.next();
ch = x.charAt(0);
y = Character.toUpperCase(ch);
} while ( y =='A'|| y=='B'|| =='D'); //etc.
return y;
What is the problem with my code?

Answer 1

What is the problem with my code?Looking at the first code example you give:do {
   /* prompting - looking for Q F or C */
} while ( y !='Q'|| y!='F'|| y!='C');Suppose I enter an 'X'. Then y!='Q' will be true and the loop will continue (good).
Next suppose I enter an 'F'. Then y!='Q' will be true and the loop will still continue (bad).
The problem here is your use of || (or). In fact you mean && (and). That way all parts of the condition have to be true in order for the loop to continue. do {
   /* prompting - looking for Q F or C */
} while ( y !='Q'&& y!='F'&& y!='C');Now when I enter an 'X': y!='Q' is true, y!='F' is true, y!='C' is true. All true so the loop continues.
When I enter an 'F': y!='Q' is true, y!='F' is false, y!='C' is true. They are not all true so the loop does not continue.
[Edit] Slow...