Objective C Tutorial - Objective C Arrays
Array is a data structure to store a fixed-size sequential collection of elements of the same type.
Declaring Arrays
To declare an array in Objective-C, we use the following syntax.
type arrayName [ arraySize ];
type defines the data type of the array elements.
type can be any valid Objective-C data type.
arraySize sets the element count inside the array. arraySize must be an integer constant greater than zero
The following line of code defines a 10-element array called myArray of type double.
double myArray[10];
Initializing Arrays
We can initialize an array using a single statement as follows:
double myArray[5] = {1.0, 2.0, 3.4, 12.0, 52.0};
The number of values in { } can not be larger than the number
of elements that we declare in [].
We can omit the size of the array and the compiler will create an array just big enough to hold the initialization.
double myArray[] = {1.0, 2.0, 3.4, 11.0, 23.0};
Array element index starts from 0, the following line sets the value for the fifth element.
myArray[4] = 5.0;
Example
#import <Foundation/Foundation.h>
int main ()
{
int n[ 10 ];
int i,j;
for ( i = 0; i < 10; i++ )
{
n[ i ] = i + 100; /* set element at location i to i + 100 */
}
for (j = 0; j < 10; j++ )
{
NSLog(@"Element[%d] = %d\n", j, n[j] );
}
return 0;
}
Creating an Array
#import <Foundation/Foundation.h>
int main ()
{
NSString *object1 = @"Hello";
NSString *object2 = @"world!";
NSNumber *object3 = [NSNumber numberWithInt:45];
NSArray *myArray;
myArray= [NSArray arrayWithObjects: object1, object2, object3, nil];
NSLog(@"Array contents = %@",[myArray componentsJoinedByString:@", "]);
return 0;
}
The code above generates the following result.
Accessing All Items in an Array
#import <Foundation/Foundation.h>
int main ()
{
NSString *object1 = @"Hello";
NSString *object2 = @"world!";
NSString *object3 = @"Good-bye";
NSArray *myArray;
myArray= [NSArray arrayWithObjects: object1, object2, object3, nil];
for (NSString *randomVariable in myArray)
{
NSLog (@"Array element = %@", randomVariable);
}
return 0;
}
The code above generates the following result.
Accessing All Items in an Array for loop
#import <Foundation/Foundation.h>
int main ()
{
NSString *object1 = @"Hello";
NSString *object2 = @"world!";
NSNumber *object3 = [NSNumber numberWithInt:45];
NSArray *myArray;
myArray= [NSArray arrayWithObjects: object1, object2, object3, nil];
int i;
for (i = 0; i < [myArray count]; i++)
{
NSLog (@"Element %i = %@", i, [myArray objectAtIndex: i]);
}
return 0;
}
The code above generates the following result.
Accessing an Item in an Array
#import <Foundation/Foundation.h>
int main ()
{
NSString *object1 = @"Hello";
NSString *object2 = @"world!";
NSNumber *object3 = [NSNumber numberWithInt:45];
NSArray *myArray;
myArray= [NSArray arrayWithObjects: object1, object2, object3, nil];
NSLog(@"Array contents = %@",[myArray componentsJoinedByString:@", "]);
NSLog (@"Index position 1 = %@", [myArray objectAtIndex:1]);
return 0;
}
The code above generates the following result.
Store Reference Objects to an Array
#import <Foundation/Foundation.h> int main (int argc, const char * argv[]) { NSMutableArray *listOfLetters = [NSMutableArray arrayWithObjects:@"A", @"B", @"C", nil]; NSString *stringObject1 = [listOfLetters objectAtIndex:0]; NSLog(@"stringObject1 = %@", stringObject1); NSString *stringObject2 = [listOfLetters lastObject]; NSLog(@"stringObject2 = %@", stringObject2); NSUInteger position = [listOfLetters indexOfObject:@"B"]; NSLog(@"position = %lu", position); return 0; }
The code above generates the following result.
Adding Items to an Array
#import <Foundation/Foundation.h>
int main ()
{
NSString *object1 = @"Hello";
NSString *object2 = @"world!";
NSString *object3 = @"Good-bye";
NSMutableArray *myArray;
myArray= [NSMutableArray arrayWithObjects: object1, object2, object3, nil];
for (NSString *randomVariable in myArray)
{
NSLog (@"Array element = %@", randomVariable);
}
[myArray addObject: @"New item"];
NSLog (@"**********");
for (NSString *randomVariable in myArray)
{
NSLog (@"Array element = %@", randomVariable);
}
return 0;
}
The code above generates the following result.
Counting Items Stored in an Array
#import <Foundation/Foundation.h>
int main ()
{
NSString *object1 = @"Hello";
NSString *object2 = @"world!";
NSNumber *object3 = [NSNumber numberWithInt:45];
NSArray *myArray;
myArray= [NSArray arrayWithObjects: object1, object2, object3, nil];
NSLog(@"Array contents = %@",[myArray componentsJoinedByString:@", "]);
NSLog (@"Total number of items in array = %i", [myArray count]);
return 0;
}
The code above generates the following result.
Deleting All Instances of an Item From an Array
#import <Foundation/Foundation.h>
int main ()
{
NSString *object1 = @"Hello";
NSString *object2 = @"world!";
NSString *object3 = @"Good-bye";
NSString *object4 = @"Hello";
NSString *object5 = @"More data";
NSString *object6 = @"Hello";
NSString *object7 = @"Last data";
NSMutableArray *myArray;
myArray= [NSMutableArray arrayWithObjects: object1, object2, object3, object4, object5, object6, object7, nil];
NSLog (@"***** Original array *****");
for (NSString *randomVariable in myArray)
{
NSLog (@"Array element = %@", randomVariable);
}
NSLog (@"***** Deleting last array item *****");
[myArray removeLastObject];
for (NSString *randomVariable in myArray)
{
NSLog (@"Array element = %@", randomVariable);
}
NSLog (@"***** Deleting item at index position 2 *****");
[myArray removeObjectAtIndex: 2];
for (NSString *randomVariable in myArray)
{
NSLog (@"Array element = %@", randomVariable);
}
NSLog (@"***** Deleting all instances of Hello *****");
[myArray removeObject: @"Hello"];
for (NSString *randomVariable in myArray)
{
NSLog (@"Array element = %@", randomVariable);
}
return 0;
}
The code above generates the following result.
Inserting Items in an Array
#import <Foundation/Foundation.h>
int main ()
{
NSString *object1 = @"Hello";
NSString *object2 = @"world!";
NSString *object3 = @"Good-bye";//[NSNumber numberWithInt:45];
NSMutableArray *myArray;
myArray= [NSMutableArray arrayWithObjects: object1, object2, object3, nil];
for (NSString *randomVariable in myArray)
{
NSLog (@"Array element = %@", randomVariable);
}
[myArray insertObject: @"New item" atIndex: 1];
NSLog (@"**********");
for (NSString *randomVariable in myArray)
{
NSLog (@"Array element = %@", randomVariable);
}
return 0;
}
The code above generates the following result.
Array Iteration
#import <Foundation/Foundation.h> @interface Class1 : NSObject -(void)reportState; -(NSString *) doSomethingSpecial; @end @implementation Class1 -(void)reportState{ NSLog(@"Class1 objects are reporting state: One"); } -(NSString *) doSomethingSpecial{ return @"Class One objects do something special"; } @end #import <Foundation/Foundation.h> @interface Class2 : NSObject -(void)reportState; @end @implementation Class2 -(void)reportState{ NSLog(@"Class2 objects are reporting state: Two"); } @end int main (int argc, const char * argv[]) { NSMutableString *string1 = [NSMutableString stringWithString:@"A"]; NSMutableString *string2 = [NSMutableString stringWithString:@"B"]; NSMutableString *string3 = [NSMutableString stringWithString:@"C"]; NSArray *listOfObjects = [NSArray arrayWithObjects:string1, string2, string3, nil]; for(NSMutableString *s in listOfObjects){ NSLog(@"This string in lowercase is %@", [s lowercaseString]); } [listOfObjects makeObjectsPerformSelector:@selector(appendString:) withObject:@"-MORE"]; [listOfObjects enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) { NSLog(@"object(%lu)'s description is %@",idx, [obj description]); }]; return 0; }
The code above generates the following result.
Save Array to a File
#import <Foundation/Foundation.h> int main (int argc, const char * argv[]) { NSArray *listOfObjects = [NSArray arrayWithObjects:@"A", @"B", @"C", [NSNumber numberWithInt:1], [NSNumber numberWithInt:2], [NSNumber numberWithInt:3], nil]; NSString *filePathName = @"/Users/Shared/array.txt"; [listOfObjects writeToFile:filePathName atomically:YES]; return 0; }
Reading Arrays from a File
#import <Foundation/Foundation.h> int main (int argc, const char * argv[]) { NSString *filePathName = @"/Users/Shared/array.txt"; NSArray *listOfObjects = [[NSArray alloc] initWithContentsOfFile:filePathName]; NSLog(@"%@", listOfObjects); return 0; }