While Loop with a Nested Switch in Objective-C

Question

I've just started learning Objective-C. I'm doing one of the standard calculator exercises. It's supposed to create an adding machine (e.g., input the operator and number, display the result each time). But I messed up something, and I think it has to do with my use of the "char" data type.

Here's the code, just the program section (interface and implementation are straightforward and worked in another version; still, if anyone wants to see them, just ask):

int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
double      value1 = 0.0;
char        operator = 'a';

Calculator *deskCalc = [[Calculator alloc] init];

NSLog(@"Initial value?");
scanf("%lf",&value1);

[deskCalc setAccumulator: value1];

while (operator != 'e') {
    {
    NSLog(@"Operation and value?");
    scanf("%c %lf", &operator, &value1);
    }
    switch (operator){
        case '+':
            [deskCalc add: value1];
            NSLog(@"%f", [deskCalc accumulator]);
            break;
        case '-':
            [deskCalc subtract: value1];
            NSLog(@"%f", [deskCalc accumulator]);
            break;
        case '*':
        case 'x':
            [deskCalc multiply: value1];
            NSLog(@"%f", [deskCalc accumulator]);
            break;
        case '/':
            if (value1 != 0) {
                [deskCalc divide: value1];
                NSLog(@"%f", [deskCalc accumulator]);
            }
            else {
                NSLog(@"Division by zero not allowed.");
                NSLog(@"%f", [deskCalc accumulator]);                   
            }
            break;
        case 's': 
            [deskCalc setAccumulator: value1];
            NSLog(@"%f", [deskCalc accumulator]);
            break;
        case 'e':
            NSLog(@"Done, sucker, final answer: %f.", value1);
        default:
            NSLog(@"Unknown operator.");
            NSLog(@"%f", [deskCalc accumulator]);
            break;
            

}
}

    [deskCalc release];
 
[pool drain];
return 0;

}

And, in case it helps, here's what I get from the terminal when I run this:

From the terminal:

Initial value?

12 // My input

Operation and value?

x 4 // My input

Unknown operator.

Operation and value? // It doesn't stop to ask for input.

48.000000

Operation and value?

Help and thanks.

P.S. I know the program is pretty clunky. Have mercy, the last language I learned was Basic on my Coleco Adam, which had a tape drive--yeah, like a cassette tape, which was awesome.

While probably not your problem, there is no break in the case for 'e'. Did you intend to do that? — Andy, May 23 '11 at 15:09
Note that in such cases it's always helpful to check what the actual value is, either by checking it in the debugger or printing it out (in this case probably as a hex or decimal value). — Georg Fritzsche, May 23 '11 at 16:09

score 4 · Accepted Answer · answered May 23 '11 at 15:19

4

scanf(" %c %lf", &operator, &value1);

Put a space between the open quotes and the %c, to trap any whitespace that is remaining on stdin.

answered May 23 '11 at 15:19

Amy Worrall

16,250
3
42
65

1

For the record, the steps I took to debug this are as follows: I got the code running, and noted that the behaviour matched what you described. Since it was saying "unknown operator", I made it log which operator it had found, with `NSLog(@"Operator '%c', operator);`. When I ran it again, I could see that the unknown operator was a carriage return. I then googled how to get scanf to skip over a carriage return, and found that a space character would do it. – Amy Worrall May 25 '11 at 07:52

score 0 · Answer 2 · answered May 23 '11 at 16:00

0

operator is mostly \n. You will probably need to do a flushall().

answered May 23 '11 at 16:00

Deepak Danduprolu

44,595
12
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105

While Loop with a Nested Switch in Objective-C

2 Answers2