An instance of a variable can be

1. stored directly in memory
2. accessed by pointer
3. accessed by reference

1. Directly Storage

• The type of a variable has no modifiers.
• The object takes up exactly its size in memory

Cube c;
int i;
uiuc::HSLAPixel p;

2. Storage by Pointer

• The type of a variable is modified with an asterisk (*).
• A pointer takes a “memory address width” of memory (ex: 64 bits on a 64 bit system)
• The pointer “points” to the allocated space of the object.

Cube *c;
int *i;
uiuc::HSLAPixel *p;

3. Storage by Reference

• A reference is an alias to existing memory and is denoted in the type with an ampersand (&).
• A reference does not store memory itself, it is only an alias to another variable.
• The alias must be assigned when the variable is initialized.
• Reference only refer to existing memory. So, its size is zero!

Cube &c = cube; // Alias to the variable `cube`
int &i = count; // Alias to the variable `i`
uiuc::HSLAPixel &p; // Illegal! Must alias something when variable is initialized.