class - Difference between a property and a global variable [objective c] -

i'm wondering difference between class's public global variable , class's property (objective-c ios programming). thing notice have use pointer notation -> access class's global variable rather dot.

i've read changing code using globals using properties can program breaking change. true , if so, why?

thanks!

edit:

block.h

public global variable (i think?) [edit: understand instance variable, thanks]

@interface block : gameobject {     @public    int type;    skemitternode *particles;} 

property

@property (nonatomic) cgfloat x; 

no, not "global variable".

it called instance variable.

a property (but not necessarily) has associated instance variable, modern compilers hide you.

the big difference between using instance variable is, property accessed through accessors (in case setx:(cgfloat)x?and -(cgfloat)x`.

if wanted, overwrite these accessors , special handling, say, whenever variable accessed.

it possible bypass accessors using instance variable directly. in case of auto-synthesized ivar, _x.

note -> not necessary in either case