The traditional for loop in Objective-C is inherited from standard C and takes the following form:
for (/* Instantiate local variables*/ ; /* Condition to keep looping. */ ; /* End of loop expressions */)
{
// Do something.
}
For example, to print the numbers from 1 to 10, you could use the for loop:
for (int i = 1; i <= 10; i++)
{
NSLog(@"%d", i);
}
On the other hand, the for in loop was introduced in Objective-C 2.0, and is used to loop through objects in a collection, such as an NSArray instance. For example, to loop through a collection of NSString objects in an NSArray and print them all out, you could use the following format.
for (NSString* currentString in myArrayOfStrings)
{
NSLog(@"%@", currentString);
}
This is logically equivilant to the following traditional for loop:
for (int i = 0; i < [myArrayOfStrings count]; i++)
{
NSLog(@"%@", [myArrayOfStrings objectAtIndex:i]);
}
The advantage of using the for in loop is firstly that it's a lot cleaner code to look at. Secondly, the Objective-C compiler can optimize the for in loop so as the code runs faster than doing the same thing with a traditional for loop.
Hope this helps.