Functions



function is a concept for C programming language, objective-c is entirely relies on C.




To define a function, you need provide four components: return value, function name, parameters and code block.


like this:




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​​int​​​​getRandomInteger(​​​​int​​​​minimum, ​​​​int​​​​maximum) {​​


​​return​​​​arc4random_uniform((maximum - minimum) + 1) + minimum;​​


​​}​​



the return value is a integer value, function name is getRandownInteger, there are two paramters: minimum and maximum, code block is enclosed by braces.




Function also can use pointer reference as return value or paramaters, like this:





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​​NSString​​​​*getRandomMake(​​​​NSArray​​​​*makes) {​​


​​int​​​​maximum = (​​​​int​​​​)[makes count];​​


​​int​​​​randomIndex = arc4random_uniform(maximum);​​


​​return​​​​makes[randomIndex];​​


​​}​​





The declaration and implementation can be sepearted, the declaration tells the compiler that these is a function and the implementation do the real work.




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​​// Declaration​​


​​NSString​​​​*getRandomMake(​​​​NSArray​​​​*);​​


​​// Implementation​​


​​NSString​​​​*getRandomMake(​​​​NSArray​​​​*makes) {​​


​​int​​​​maximum = (​​​​int​​​​)[makes count];​​


​​int​​​​randomIndex = arc4random_uniform(maximum);​​


​​return​​​​makes[randomIndex];​​


​​}​​



If a method want call function , the function declaration should be defined before the method.




static word




static functions




By default, all functions have a global scope, if you want limit the function’s scope to the current file, use ‘static’ keyword:





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​​// Static function declaration​​


​​static​​​​int​​ ​​getRandomInteger(​​​​int​​​​,​​​​int​​​​);​​


​​// Static function implementation​​


​​static​​​​int​​ ​​getRandomInteger(​​​​int​​​​minimum, ​​​​int​​​​maximum) {​​


​​return​​​​arc4random_uniform((maximum - minimum) + 1) + minimum;​​


​​}​​



Note that static keyword should be use on both the function declaration and implementation.




static local variable


By defualt, the local variable in a function will be reset each time the function is called. If you use ‘static’ midifier on a local variable in a function , the variable value will be remembered.


Note that the local variable’s scope do not changed, it still only accessible inside the function itself.