add new object to nsmutablearray replace all objects in array - ios

Question

i try to add new object to my nsmutablearray but every time it replace all object
-(void)addToStack:(Coordinate *)coord{
Coordinate*c = [[Coordinate alloc] init];
c.x=coord.x;
c.y = coord.y;
if (coord.x==0 && coord.y==0) {
c.x=coord.x+1;
[_stack addObject:c];
c.x=coord.x;
c.y=coord.y+1;
[_stack addObject:c];
c.y=coord.y;
}
}

Answer 1

You are not adding a new object but you are changing the old object where the reference will remain the same.
NSMutableArray addObject will not add it because it already exists in the array.
So, when trying to add a new object, first create a copy of the one that you want to change, like this:
Coordinate *newCoordinate = [Coordinate mutableCopy];
// change attributes
// add it to the array

Answer 2

Everybody who said that adding the same object twice deletes the first instance and replaces it, is wrong.
Arrays can contain duplicate references to the same object. However, it's more like saving the same street address in an rolodex twice. If you look up the address in the first entry, go break all the windows in that house, then go back, look up the address in the second slot in your rolodex, and drive to THAT address, you'll find the house has broken windows (Because both addresses point to the same house.)
Similarly, when you add the same object to an array twice, it's two pointers to the same object. When you change values of the object at index 0, you see those changes reflected in the object in index 1 because it's a second pointer to the same object.
Despite saying the wrong thing about what goes wrong with your code, #Shashi3456643 gave you the correct solution, which is to create a new, unique object for every entry in your array.

Answer 3

Make sure to initiate the array:
NSMutableArray *stack=[[NSMutableArray alloc] init];

Answer 4

This is because every time you init the array. Initialize the array once.
For example:
in .h
Coordinate*c;
in .m
- (void)viewDidLoad
{
c = [[Coordinate alloc] init];
}
-(void)addToStack:(Coordinate *)coord{
c.x=coord.x;
c.y = coord.y;
if (coord.x==0 && coord.y==0) {
c.x=coord.x+1;
[_stack addObject:c];
c.x=coord.x;
c.y=coord.y+1;
[_stack addObject:c];
c.y=coord.y;
}
}