exercise 6.4

[dharr19]

Hi Stephen,

I am working practice exercise 6.4.  If I type in an 'E' or 'e' it still goes thru the switch statement.  Here is part of the program that does the work in blue.  And below this is the output in orange

    NSLog(@"Type in your expression.");
    scanf("%lf %c", &value, &operator);
   
    [deskcalc setAccumulator:value];
   
    while (operator != 'E' || operator != 'e')
    {
        switch ( operator )
        {
            case '+':
               [deskcalc add:value];
                break;
            case '-':
               [deskcalc subtract:value];
               break;
            case '*':
            case 'x':
               [deskcalc multiply:value];
               break;
            case '/':
               [deskcalc divide:value];
               break;
            case 'S':
            case 's':
                [deskcalc setAccumulator:value];
                break;
            default:
               Error = 1;
               NSLog(@"Unknown operator %c.", operator);
               break;
        }
   
        NSLog(@"%f", [deskcalc accumulator]);       
        scanf("%lf %c", &value, &operator);
    }
   
    NSLog(@"%lf %c End of program = ", [deskcalc accumulator], operator);
    NSLog(@"End of calculations.");
   
   2011-07-11 12:59:08.377 Calculator[1383:903] Type in your expression.
    0 E
    2011-07-11 12:59:16.250 Calculator[1383:903] Unknown operator E.
    2011-07-11 12:59:16.250 Calculator[1383:903] 0.000000

[skochan]

Look at the logic in your while statement.

Cheers,

Steve

[dharr19]

If I write the statement as follows it works fine

while (operator != 'E')

but if I do the following it won't

while ((operator != 'E') || (operator != 'e'))

[skochan]

You want to use a logical AND and write the expression like this:

Code: (Objective-C)

while (operator != 'E' && operator != 'e')
   ...

Cheers,

Steve