Question

I am creating a program in the iOS SDK in which there is a group of buttons. When a button is clicked, its title is added to an array, and the array is displayed in an assigned label.

When I try to create delete and clear buttons, error messages show up. They show up in the function_builder = function_builder.removeLastObject; and function_builder = function_builder.removeAllObjects; lines of the .m file. The error messages are the same: Assigning to ‘NSMutableArray *_strong’ from incompatible type ‘void’. How do I fix this?
Thank you for any and all help

Here is the .h file:

#import <UIKit/UIKit.h>

@interface SecondViewController : UIViewController
@property (nonatomic,strong) IBOutlet UILabel *equation_field;
@property (nonatomic) NSMutableArray *function_builder;//declare array//
@property(nonatomic, readonly, retain) NSString *currentTitle;//declare button titles//
@end

And here is the .m file:

#import "SecondViewController.h"

@interface SecondViewController ()

@end

@implementation SecondViewController
@synthesize equation_field;
@synthesize currentTitle;
@synthesize function_builder;
NSMutableArray *function_builder;//create the array name//

- (IBAction)functionButtonPress:(UIButton *)sender {//code for all buttons except delete    and clear//
[function_builder addObject: sender.currentTitle];//when button is pressed, its title is added to the array//
self.equation_field.text = function_builder.description;//the contents of the array appear in the assigned label//
}
- (IBAction)delete:(UIButton *)sender {//create delete button//
function_builder = function_builder.removeLastObject; //ERROR OCCURRING HERE: Assigning to 'NSMutableArray *_strong' from incompatible type 'void'//
}

- (IBAction)clear:(UIButton *)sender{//create clear button//
function_builder = function_builder.removeAllObjects;//ERROR OCCURRING HERE: Assigning to 'NSMutableArray *_strong' from incompatible type 'void'//
}



- (void)viewDidLoad {

function_builder = [[NSMutableArray alloc] init];//initialize array//



[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}

- (void)viewDidUnload
{
[super viewDidUnload];
// Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
} else {
    return YES;
}
}

@end

Answer 1

Many errors there..

You’ve assigned the results of this methods (void*) to function_builder which is of kind NSMutableArray. That makes no sense.

In order to manipulate an object, just send a message to it:

[function_builder removeLastObject]; // this will remove the last object of the array
[function_builder removeAllObjects]; // guess what ;)

For the other thing:

self.equation_field.text = [function_builder componentsJoinedByString:@", "]

This will create a string with all objects in array separated by “, ” => A, B, C, D