In Objective-C, you can declare a variable in two places. First, you can declare it in between the braces of the header file for your class. Then it becomes an instance variable. Second, you can declare it within a method in the implementation file for your class.
The compiler needs to be informed about every type before you use it. That means you must import the header file into any implementation that uses the variable. To see the ParseError that you get if you fail to do this, see ParseErrorAtCertainNameNeedHelp.
You declare a variable by first defining the variable’s type, then you write the name of the variable, and you end the declaration with a semicolon.
short myShortVariable;
This declaration defines a variable that is of the type “short” and which is named “myShortVariable”.
You can declare more than one variable at a time…
float x,y,z;
Here we are declaring three variables of the type “float” which are named “x”, “y”, and “z”.
Cocoa objects are declared with a style similar to that of declaring C pointers
Declaration of Cocoa objects as parameters and return values is best presented as an example of the interface part of a sample class see also AnatomyOfADotHFile
1 //Pet-Class Interface (Pet.h)
2 #import <Foundation/NSObject.>
3 #import <Foundation/NSString.h>
4 @interface
5 Pet : NSObject
6 {
7 NSString *name;
8 int age;
9 }
10 - (void)setName:(NSString *)newName;
11 - (NSString *)name;
12 - (void)setAge:(int)newAge;
13 @end
Remember that the code you are writing is in Objective-C, not in C. In C you write a prototype like this:
void setName(NSString *newName);
but the Objective-C equivalent is:
- (void)setName:(NSString *)newName;
The parentheses are there because it is the way specify the type of the parameter in Objective-C. Try reading the “The Objective-C Programming Language” book from Apple: http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/index.html.
The *’ is actually a part of the type. So you are using variables of type NSString when dealing with Cocoa strings. Placing the * beneath the variable name is just an ancient C convention. The compiler will not distinguish between ‘NSString name’, ‘NSString name’ or even ‘NSString*name’, IIRC. This IS hard for a newbie - but C was written for Real� Men only, I suppose. ;-)
Remember in the interface, anything within the { } are variable declarations. Anything after the } and before the @end are method declarations.
* Line 7, name is a variable, a pointer to a NSString(NSString *) * line 10, newName is a parameter when you call the method “setName” you must pass in a pointer to an NSString (NSString *) * line 11, “name” is not a variable name but a method name, this method will return a pointer to an NSString (NSString *)
Note that declaring scalar types uses the same punctuation style in ObjC (see also the discussion on C syntax for how to declare and pass pointers to scalar types)
A good article about how to use global variables in Objective-C can be found here: GlobalVariablesInCocoa
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