macOS Switch Statement Obj-C

[larswik]

Hello. I have a method and I want to pass in a NSString which contains just a single char from an NSTextField. The return value will be an int.

If I pass in value is @"a" the return value would be 1 as an example.

-(int)findCritValue: (NSString *) letter{
    int i;
    switch (letter) {
        case @"a":
            i = 1;
            return i;
            break;
            
        default:
            break;
    }
}

I am getting an error saying the Switch only take integer values?

 

[gnasher729]

Hello. I have a method and I want to pass in a NSString which contains just a single char from an NSTextField. The return value will be an int.

If I pass in value is @"a" the return value would be 1 as an example.

-(int)findCritValue: (NSString *) letter{
    int i;
    switch (letter) {
        case @"a":
            i = 1;
            return i;
            break;
            
        default:
            break;
    }
}

I am getting an error saying the Switch only take integer values?

Exactly. The switch statement only takes integer constant values.

 

[larswik]

I must be thinking back to my Pascal class or from my C book. This link has examples of char's being used, Pascal.

http://www.schoolfreeware.com/Free_Pascal_Tutorial_8_Case_Statements_-_Lazarus.html

Perhaps Objective - C is not as cool as Pascal still is, with it's limited abilities

 

[jiminaus]

Perhaps Objective - C is not as cool as Pascal still is, with it's limited abilities

Switch being restricted to integer constants can be a PITA. It is a shame that Objective-C didn't extend C's switch to cover NSString, even if it compiles down to a cascade of if/else if/.../else.

 

[mfram]

How about something like:

-(int)findCritValue: (NSString *) letter{
    int i;
    unichar u = [letter characterAtIndex:0];
    switch (u) {
        case 'a':
            i = 1;
            return i;
            break;
            
        default:
            break;
    }
}

 

[balamw]

larswik, I think it works fine with char because char is just an unsigned 8 bit integer.

'a' is just convenient shorthand for 0x61 or decimal 97.

NSString isn't so simple. Maybe you can convert your NSString to char * in ASCII or UTF-8.

B

 

[wlh99]

larswik, I think it works fine with char because char is just an unsigned 8 bit integer.

'a' is just convenient shorthand for 0x61 or decimal 97.

NSString isn't so simple. Maybe you can convert your NSString to char * in ASCII or UTF-8.

B

Also,
Instead of 26 switch statements (assuming one for each letter) you can subtract 96 from the char for a lowercase letter, and 64 for a lowercase letter. You would also want some error checking to ensure the returned value makes sense.

-(int)findCritValue: (NSString *) letter{
    int i;
    unichar u = [letter characterAtIndex:0];
    if (u > 96) i = u-96;
    else i = u-64;
    if ((i < 1) || (i > 26)) {
        NSLog(@"Error - non letter entered");
        
        return 0;
    }
    return i;
    
    
}

 

[larswik]

Thanks for the ideas!

It's not every number, it's these letters with these values

A = 10
B = 20
C = 30
D = 50
E = 70
F = 80
G = 90
H = 100
I = 120
J = 140
K = 150
L = 160
M = 170

I think it will be easier to to use a bunch of If statements in my method and adjust the passed in argument to upper or lower case. I was a little surprised that I could not compare strings in the Switch like the 'isEqualTo' or something.

Thanks!

 

[lee1210]

Thanks for the ideas!

It's not every number, it's these letters with these values


I think it will be easier to to use a bunch of If statements in my method and adjust the passed in argument to upper or lower case. I was a little surprised that I could not compare strings in the Switch like the 'isEqualTo' or something.

Thanks!

You could try:

NSDictionary *valueMap = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt: 10], @"A",
[NSNumber numberWithInt: 20], @"B",
[NSNumber numberWithInt: 30], @"C",...];

Then

NSNumber *myValue = [valueMap valueForKey:myKey];

If myValue is null, didn't match, no good. Otherwise you can pass intValue to get your int out.

-Lee

 

[balamw]

You could try:

What a simple Cocoa way of approaching this problem.

Of course a dictionary has keys and values.

Yet another reason I find it harder and harder to recommend learning C before Objective-C/Cocoa if that is your goal. When you do you tend to miss the forest for all the trees you are used to dealing with in lower level languages.

B