struct a collection of types, composite data type, composition, “user-definded data structure” struct Test { char* name; int nr; float f; }; Name of type is “struct Test”, and not “Test” alone. struct Test myNewTest Semicolon after closing parethesis is essentional. Access composed types with dot-syntax: myNewTest.name = "hjkjnk"; myNewTest.nr = 32; myNewTest.f = 2.2424; typedef a shorthand, an alias for a type, for ease of readability. typedef int MyType “MyType n;” would be equal to “int n;” enum “introduces a symbolic name for an integer constant” enum direction_enum {LEFT, RIGHT}; /* LEFT -> 0, RIGHT -> 1; */ enum direction_enum x = LEFT; typedef enum typedef enum { LEFT; RIGHT; } direction; declatation: -(void)myFunction:(direction)LEFTorRIGHT; call: -(void)myFunction:LEFT; typedef struct typedef struct objectInfo_ { CGPoint origin; NSString* name; NSColor* color; } objectInfo Shortcut. Instead of writing ‘struct objectInfo_’, write ‘objectInfo’. The keyword ‘objectInfo_’ seems to be optional.