Question

Does someone know why i never get the first value of my array? it always starts at the index i+1, when i start the for loop at 0, or like here at 1 : instead of x=44, the console says x=100 :

//at the top
#define kMaxHillKeyPoints 5

//in the .h:
CGPoint _hillKeyPoints[kMaxHillKeyPoints];

- (void)generatePath {

    int _nVertices = 1;

    _hillKeyPoints[_nVertices] = CGPointMake(44, 0);
    _hillKeyPoints[_nVertices++] = CGPointMake(100, 75);
    _hillKeyPoints[_nVertices++] = CGPointMake(50, 150);
    _hillKeyPoints[_nVertices++] = CGPointMake(150, 225);

    for(int i = 1; i < 4; i++) {   
        CCLOG(@" _hillKeyPoints[1].x : %f", _hillKeyPoints[1].x);
        CCLOG(@"%i", i);
    }
}

//output :
_hillKeyPoints[1].x : 100.000000 //why not x = 44 ?

Would you know why? i cleaned the project also, but it does not change anything.

Thanks

Answer 1

First, you did the following:

int _nVertices = 1;
_hillKeyPoints[_nVertices] = CGPointMake(44, 0); //_nVertices = 1

This assigns _hillKeyPoints[1] to (44,0). Here, you are still good (you can NSLog here to verify).

However, in the following statement:

_hillKeyPoints[_nVertices++] = CGPointMake(100, 75);

you are post-incrementing _nVertices. This means that _hillKeyPoints[_nVertices] is first assigned to (100,75), then the value _nVertices is incremented. The statement above is exactly equivalent to doing this:

_hillKeyPoints[_nVertices] = CGPointMake(100, 75); 
_nVertices = _nVertices + 1;

Note that _nVertices = 1 here during assignment, so you are overwriting your previous assignment of (44, 0), and hence you get _hillKeyPoints[1] = (100,75) in the end.

If you still want to do it your way, you can pre-increment the index each time:

int _nVertices = 1; 
_hillKeyPoints[_nVertices] = CGPointMake(44, 0); //_nVertices = 1
_hillKeyPoints[++_nVertices] = CGPointMake(100, 75); //_nVertices = 2
_hillKeyPoints[++_nVertices] = CGPointMake(50, 150); //_nVertices = 3
_hillKeyPoints[++_nVertices] = CGPointMake(150, 225); //_nVertices = 4

Hope this helps.