In Objective-C, you can add an element to an array using the addObject: method of NSMutableArray. Here's an example:
// create a mutable array and add some initial elements
NSMutableArray *myArray = [NSMutableArray arrayWithObjects:@"Item 1", @"Item 2", nil];
// add a new element to the end of the array
[myArray addObject:@"Item 3"];
// print the updated array
NSLog(@"%@", myArray);
In this example, we create a mutable array using the arrayWithObjects: method of NSMutableArray and add two initial elements to it. Then, we use the addObject: method to add a new element "Item 3" to the end of the array. Finally, we print the updated array using NSLog().