MadIvad asks:

Is there some sort of math function for the minimum of a set of values? I have searched the docs and not found one reference to math in iPhone OS2.2, and min only returns the like of ‘minimum’ for different control values. or for stating what the minimum of the integer or NSUInt class etc…

Does a function/class/anything exist that would simply return the lowest value of 2 or more values?

Boy, that was easy. There are compiler macros defined that work on any scalar datatype. MIN(a,b) and MAX(a,b). Note the case.

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Trapper asks:

I have one integer holding a variable number of decimal places that another variable needs to be rounded to when I stringWithFormat it. What is the correct way to do this?

Trapper is not content with just specifying %.2f in a stringWithFormat, but he wants the number of decimal places to be dependent on a second variable.

Here is the shortest method I came up with.

int decimals = 3;
double d = 3.1415;
   
NSString *format = [NSString stringWithFormat:@"%%%0.1ff", decimals/10.0];
NSString *formattedString = [NSString stringWithFormat:format, d]; // e.g. %0.3f 
NSLog(formattedString);

I got confused at first because the NSLog would always output a strange value when wanted to output the formatting string. Then I remembered that the first parameter of NSLog itself is also interpreting formatting information. NSLog combines stringWithFormat into the output.

That’s good to know in case you want to add an NSLog statement for debugging floating point variables.

double d = 3.1415;
NSLog("%0.2f", d);  // formatting directly here

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Rob asks:

I have decided to start writing apps as a full time job. Assuming I can master this, and assuming I can get 1 app per month accepted in the App Store, can anyone give me some guidance on how much income I am likely to make.

Here are some numbers from my data that might help you:

• A general purpose tool app like GeoCorder might sell between 1 and 5 copies a day.
• Something interesting or unusual like iFR Cockpit can expect to sell around 5-10 copies a day.
• A niche market tool like iWoman might to do well at 10-20 copies a day.
• A game like LuckyWheel would sell around 20 copies a day IF you also have a LITE Version that has about 900-1000 downloads a day. Without a LITE version it could only be 5-10 copies a day.;-)

So assuming you concentrate on niche apps and games and calculating from $25 a day per such app you might make around $2000 a month if you manage to land 3 of those in the store. NOT taken into account additional cost like taxes or hardware. And not considering that Apple has the painful final word. Does that sound easy enough for you to immediately quit your day job?

For me it didn’t and it took me 8 months to get where I am today. It’s ok to see it as a lucrative hobby or even second income, but to stake your existance solely iPhone development you have to be extremely disciplined. Or even better: to know how to build teams of bright minds who can bring skills to the table that your don’t possess yourself.

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