l

L-value: refer to location, passing by reference.
R-value: refer to the value stored at the location, passing by value.

Reading location on the right and writing to the location on left

To run g (e):
1, evaluate e to a value v
2, pass a copy of v to g
3, callee changes to copy of v not visible to caller

To run g (e):
1, evaluate e to an l-value r
2, pass the l-value r to g
3, callee changes via r are visible to caller
Ps: l-value is reference

Array is passing by reference and other is passing by value.

Reference Type is passing by reference and other is passing by value.