Objective-C Fundamentals

Arrays
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On return, the variable numberOfItems tells you how many elements are in the array.
To access each element in an NSArray, you can use another message called objectAt-
Index:, which behaves similarly to the [] indexing operator used with C-style arrays:
id item = [myArray objectAtIndex:5];
You could imagine this last statement as being equivalent to myArray[5] if myArray
had instead been declared as a C-style array. The intent and behavior is identical.
Using the techniques you learned in this section, you could access the last element of
an array with the following code snippet:
int indexOfLastItem = [myArray count] - 1;
id item = [myArray objectAtIndex:indexOfLastItem];
You could even condense this into a single statement by nesting the two method calls:
id item = [myArray objectAtIndex:[myArray count] - 1];
The -1 in the index calculation accounts for the fact that the last element in the array
will have an index of 1 less than the number of items in the array. Because this is a
common code pattern and Foundation Kit is all about developer efficiency, NSArray
provides a lastObject message that performs the same task in a cleaner manner:
id item = [myArray lastObject];
Using this concept of simplifying common coding tasks, let’s investigate some of the
other aspects of the NSArray class.
4.1.3 Searching for array elements
You now have the building blocks for determining if a particular value is present in an
array. To achieve this goal, you can use a for loop to step through each element in the
array and use an if statement to compare the current element with the value you’re
looking for. This process is demonstrated in the following listing.
Listing 4.2
Determining if an NSArray contains the word “Fish” using C-style code
NSArray *pets = [NSArray arrayWithObjects:@"Cat", @"Dog", @"Rat", nil];
NSString *valueWeAreLookingFor = @"Fish";
int i;
BOOL found = NO;
for (i = 0; i < [pets count]; i++)
{
if ([[pets objectAtIndex:i]
isEqual:valueWeAreLookingFor])
{
found = YES;
break;
}
}
B
d
Step through
the array
c
Check array
element value
Break out
for loop
if (found)
{