--- title: "Objective-C : Arrays" description: "Objective-C programming language provides a data structure called the array, which can store a fixed-size sequential collection of elements of the sam" author: "Tarun Kumar" published: 2015-07-09 updated: 2019-09-07 canonical: https://www.mindstick.com/articles/1816/objective-c-arrays category: "iphone" tags: ["iphone", "ios", "objective c"] reading_time: 9 minutes --- # Objective-C : Arrays *Previously we learn how to define numbers type with NSNumber* : Objective-C : Numbers\ Objective-C [programming language](https://www.mindstick.com/articles/332896/top-5-programming-languages-for-ios-app-development) provides a [data structure](https://www.mindstick.com/articles/332406/why-it-is-important-to-learn-data-structure-and-algorithm) called the array, which can store a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type. Instead of declaring individual variables, such as number0, number1, ..., and number99, you declare one array variable such as numbers and use numbers[0], numbers[1], and ..., numbers[99] to represent individual variables. A specific element in an array is accessed by an index. All arrays consist of contiguous memory locations. The lowest address corresponds to the first element and the highest address to the last element. \ ![Objective-C : Arrays](https://www.mindstick.com/mindstickarticle/86d44897-a5dc-442f-bdaf-3c642a893f15/images/4e714852-a378-4409-90b7-433ad6e80805.png) \ ##### Declaring Arrays \ To declare an array in Objective-C, a programmer specifies the type of the elements and the number of elements required by an array as follows: ``` type arrayName [arraySize ]; ``` \ This is called a single-dimensional array. The arraySize must be an integer constant greater than zero and type can be any valid Objective-C data type. For example, to declare a 10-element array called balance of type double, use this statement: *\* ``` double balance[10]; ``` Now, balance is a variable array, which is sufficient to hold up to 10 double numbers. ##### Initializing Arrays **\** You can initialize an array in Objective-C either one by one or using a single statement as follows: ``` double balance[5] = {1000.0, 2.0, 3.4, 17.0, 50.0}; ``` The number of values between braces { } can not be larger than the number of elements that we declare for the array between square brackets [ ]. Following is an example to assign a single element of the array: If you omit the size of the array, an array just big enough to hold the initialization is created. Therefore, if you write: ``` double balance[] = {1000.0, 2.0, 3.4, 17.0, 50.0}; ``` You will create exactly the same array as you did in the previous example. ``` balance[4] = 50.0; ``` The above statement assigns element number 5th in the array a value of 50.0. Array with 4th index will be 5th, i.e., last element because all arrays have 0 as the index of their first element which is also called base index. Following is the pictorial representation of the same array we discussed above: \ ![Objective-C : Arrays](https://www.mindstick.com/mindstickarticle/86d44897-a5dc-442f-bdaf-3c642a893f15/images/0029bc57-148c-4892-84f8-edc7d266c612.png) ##### Accessing Array Elements \ An element is accessed by indexing the array name. This is done by placing the index of the element within square brackets after the name of the array. For example: ``` double salary = balance[9];  ``` The above statement will take 10th element from the array and assign the value to salary variable. ##### Finding out the Number of Elements in an Array \ The number of objects in an array ([referred to as](https://answers.mindstick.com/qa/97098/which-layers-are-referred-to-as-network-support-layers) elements) can be identified using the count instance method of the NSArray class: ``` #import int main (){    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];        NSArray *myColors;          myColors = [NSArray arrayWithObjects: @"Red", @"Green", @"Blue", @"Yellow", nil];    NSLog (@"Number of elements in array = %lu", [myColors count]);        [pool drain];    return 0;} ``` When executed, the above code will be displayed: ``` 2015-07-10 02:35:11.472 demo[27440] Number of elements in array = 4 ``` ##### \ ##### Accessing the Elements of an Array Object ## \ The objects contained in an array are given index positions beginning at position zero. Each element may be accessed by passing the required index position through as an argument to the NSArray *objectAtIndex* instance method. We can, therefore, now extend our array example to display each element, using the count method to identify in advance how many elements there are to display: ``` #import int main () { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; NSArray *myColors; int i; int count; myColors = [NSArray arrayWithObjects: @"Red", @"Green", @"Blue", @"Yellow", nil]; count = [myColors count]; for (i = 0; i < count; i++) NSLog (@"Element %i = %@", i, [myColors objectAtIndex: i]); [pool drain]; return 0; } ``` When run, the above code will display each element in the array object: ``` 2015-07-10 02:42:42.667 demo[32249] Element 0 = Red2015-07-10 02:42:42.668 demo[32249] Element 1 = Green2015-07-10 02:42:42.668 demo[32249] Element 2 = Blue 2015-07-10 02:42:42.668 demo[32249] Element 3 = Yellow ``` ##### Accessing Array Elements using Fast Enumeration \ The technique for accessing all the array elements using a *for* loop as described in the previous section is a little ungainly. Another, easier mechanism for accessing [element in an array](https://www.mindstick.com/forum/158838/write-a-rust-program-to-find-the-second-smallest-element-in-an-array) involves something called *fast enumeration*. Fast enumeration simply requires that a variable be declared to hold each array element, and then referenced in the for loop: ``` #import int main (){    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];        NSArray *myColors;    NSString *color;    myColors = [NSArray arrayWithObjects: @"Red", @"Green", @"Blue", @"Yellow", nil];    for (color in myColors)        NSLog (@"Element = %@", color);    [pool drain];    return 0;} ``` When run, the above code will display each element in the array object: ``` 2015-07-10 02:50:21.1000 demo[3758] Element = Red2015-07-10 02:50:22.001 demo[3758] Element = Green2015-07-10 02:50:22.001 demo[3758] Element = Blue 2015-07-10 02:50:22.001 demo[3758] Element = Yellow ``` ##### Adding Elements to an Array Object ## \ New elements may be added to a [mutable array](https://www.mindstick.com/forum/33695/sorting-mutable-array-in-ascending-order-in-objective-c) object using the *addObject* instance method of the NSMutableArray class. For example, to [declare and initialize](https://www.mindstick.com/forum/159225/how-can-i-declare-and-initialize-an-array-in-java) an array, and then later add new element object the following code might be used: ``` #import int main () { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; NSMutableArray *myColors; NSString *color; myColors = [NSMutableArray arrayWithObjects: @"Red", @"Green", @"Blue", @"Yellow", nil]; //Before Adding Elements for (color in myColors) NSLog (@"Before Adding Element = %@", color); [myColors addObject: @"Indigo"]; [myColors addObject: @"Violet"]; //After Adding Elements for (color in myColors) NSLog (@"After Adding Element = %@", color); [pool drain]; return 0; } ``` When run, the above code will display each element in the array object: ``` 2015-07-10 03:02:43.767 demo[9598] Before Adding Element = Red2015-07-10 03:02:43.768 demo[9598] Before Adding Element = Green2015-07-10 03:02:43.768 demo[9598] Before Adding Element = Blue 2015-07-10 03:02:43.768 demo[9598] Before Adding Element = Yellow2015-07-10 03:02:43.768 demo[9598] After Adding Element = Red 2015-07-10 03:02:43.768 demo[9598] After Adding Element = Green 2015-07-10 03:02:43.768 demo[9598] After Adding Element = Indigo2015-07-10 03:02:43.768 demo[9598] After Adding Element = Blue 2015-07-10 03:02:43.768 demo[9598] After Adding Element = Yellow 2015-07-10 03:02:43.768 demo[9598] After Adding Element = Violet ``` ##### Inserting Elements into an Array ## \ The previous method appends new objects onto the end of an array. It is also possible to insert new objects at specific index points in an array object using the *insertObject* instance method. This method accepts as arguments the object to be inserted and the index position at which the insertion is to take place: ``` #import int main (){    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];        NSMutableArray *myColors;    int i;    int count;    myColors = [NSMutableArray arrayWithObjects: @"Red", @"Green", @"Blue", @"Yellow", nil];    [myColors insertObject: @"Indigo" atIndex: 1];    [myColors insertObject: @"Violet" atIndex: 3];    count = [myColors count];     for (i = 0; i < count; i++)        NSLog (@"Element %i = %@", i, [myColors objectAtIndex: i]);    [pool drain];    return 0;} ``` When we compile and run the code, the output will be like this: ``` 2015-07-10 03:04:17.131 demo[10617] Element 0 = Red2015-07-10 03:04:17.132 demo[10617] Element 1 = Indigo2015-07-10 03:04:17.132 demo[10617] Element 2 = Green 2015-07-10 03:04:17.132 demo[10617] Element 4 = Blue2015-07-10 03:04:17.132 demo[10617] Element 3 = Violet 2015-07-10 03:04:17.132 demo[10617] Element 5 = Yellow ``` ##### Deleting Elements from an Array Object \ The NSMutableArray class provides a number of [instance methods](https://www.mindstick.com/forum/23099/difference-between-static-methods-and-instance-methods-in-java) designed specifically to remove one or more elements from an array object. A sample of some of the more commonly used methods is provided below. This list is not exhaustive so refer to the Foundation Framework documentation for the NSMutableArray class for a full listing. To remove an element at a specific index location, use the removeObjectAtIndex method and ###### ##### To remove the first instance of a specific object from an array use removeObject: ``` #import int main (){    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];        NSMutableArray *myColors;    int i, count;    myColors = [NSMutableArray arrayWithObjects: @"Red", @"Green", @"Blue", @"Yellow", nil];    [myColors removeObject: @"Yellow"];    [myColors removeObjectAtIndex: 0];    count = [myColors count];    for(i=0; iint main (){    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];        NSMutableArray *myColors;    int i, count;    myColors = [NSMutableArray arrayWithObjects: @"Red", @"Green", @"Blue", @"Yellow", @"Red", @"Red", nil];    [myColors removeObjectIdenticalTo: @"Red"];    count = [myColors count];    for(i=0; i int main () { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; int i, count; NSMutableArray *myColors = [NSMutableArray arrayWithObjects: @"red", @"green", @"blue", @"yellow", nil]; NSArray *sortedArray; sortedArray = [myColors sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)]; count = [sortedArray count]; for(i=0; i