Convert javascript function to Obj-C function

Question

I want to use a bunch of functions that were written in Javascript in my Obj-C app. I made a header file and got the first one converted, but got stuck on the second. Here's what I started with and what I've done so far that doesn't work...

function calcDayOfWeek(juld)
    {
        var A = (juld + 1.5) % 7;
        var DOW =     (A==0)?"Sunday":(A==1)?"Monday":(A==2)?"Tuesday":(A==3)?"Wednesday":(A==4)?"Thursday":(A==5)?"Friday":"Saturday";
        return DOW;
    }

...and my attempt:

NSString calcDayOfWeek(float julianDay)
{
    float A = (julianDay + 1.5) % 7;
    NSString DOW = (A==0)?"Sunday":(A==1)?"Monday":(A==2)?"Tuesday":(A==3)?"Wednesday":(A==4)?"Thursday":(A==5)?"Friday":"Saturday";
    return DOW;
}

It should return a string with the day of the week based on the input of a Julian Day Number.

EDIT: Per Yuji's answer, this is what worked...

NSString* calculateDayOfWeek(float julianDay) {
    int a = fmod(julianDay + 1.5, 7);
    NSString* dayOfWeek = (a==0)?@"Sunday":(a==1)?@"Monday":(a==2)?@"Tuesday":(a==3)?@"Wednesday":(a==4)?@"Thursday":(a==5)?@"Friday":@"Saturday";
    return dayOfWeek;
}

Yuji · Accepted Answer · 2010-12-03 04:35:47Z

5

You first need to learn the syntax and the grammar of Objective-C. The function would be

NSString* calcDayOfWeek(float julianDay)
{
     int A = ((int)(julianDay + 1.5)) % 7;
     NSString* DOW = (A==0)?@"Sunday":(A==1)?@"Monday":(A==2)?@"Tuesday":(A==3)?@"Wednesday":(A==4)?@"Thursday":(A==5)?@"Friday":@"Saturday";
     return DOW;
}

In Objective-C, variables for objects are pointers, not the object itself. You need NSString* instead of NSString.
@"..." is the Objective-C string which is an object. "..." is a C-string, which is just char*.
I recommend against using == for a float. What happens if two floats differ by .00000001? Well, % operator automatically gives you integer, but I still don't like it.

However, you shouldn't re-invent the wheel. Cocoa has an API that does the calendar conversion for you. See Date and Time Programming Topics.

edited Dec 3, 2010 at 4:35

answered Dec 3, 2010 at 4:10

Yuji

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5 Comments

Steve Over a year ago

Of the suggestions, this gets the closest. But the int A = (julianDay + 1.5) % 7; line generates two instances of error: invalid operands to binary % (have 'double' and 'int')

Steve Over a year ago

I searched for that error and tried this instead: int A = fmod(julianDay, 7); This compiles fine - now to try it. And thanks for the link to the date/time stuff!

Yuji Over a year ago

Ah, sorry. I had no idea that % doesn't accept float and int!

Andrew Over a year ago

I've been curious about this for a while and it's impossible to google: What's the difference between NSString* calcDayOfWeek()... in your answer and NSString *calcDayOfWeek()... in @ConspicuousCompiler's one? Does moving the * have a syntactic impact?

Yuji Over a year ago

No it doesn't. Read the specification of the programming language C: open-std.org/JTC1/SC22/WG14/www/docs/n1256.pdf Basically, any spaces to the right or to the left of non-alphabetic character mean nothing to the language. You can just remove them. NSString*calc... would be just fine.

Sam Ritchie · Accepted Answer · 2010-12-03 04:07:20Z

1

You'll need to change the way you declare the function. Try this:

-(NSString *) dayOfWeek:(float)julianDay {

    float A = (julianDay + 1.5) % 7;
    NSString *DOW = (A==0)?@"Sunday":(A==1)?@"Monday":(A==2)?@"Tuesday":(A==3)?@"Wednesday":(A==4)?@"Thursday":(A==5)?@"Friday":@"Saturday";
    return DOW;
}

answered Dec 3, 2010 at 4:07

Sam Ritchie

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Comments

Moshe · Accepted Answer · 2010-12-03 04:24:51Z

1

You'll want to build your strings as NSStrings by prefixing them with @s and take a reference to them:

NSString *calcDayOfWeek(float julianDay)
{
    float A = (julianDay + 1.5) % 7;
    NSString *DOW = (A==0)?@"Sunday":(A==1)?@"Monday":(A==2)?@"Tuesday":(A==3)?@"Wednesday":(A==4)?@"Thursday":(A==5)?@"Friday":@"Saturday";
    return DOW;
}

edited Dec 3, 2010 at 4:24

Moshe

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answered Dec 3, 2010 at 4:06

Conspicuous Compiler

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