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;
}

Answer 1

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.