Initialization
Initialization is not assignment
Initialization happens when a variable is given a value when it is created. Assignment obliterates an object’s current value and replaces that value with a new one.
For default initialization,variables of build-in type outside any blocks are initialized to zero, while inside function body being uninitialized. Class types have different initialization rules.
Declarations and Definitions
Variables must be defined exactly once(in one file) but can be declared many times(in other files).
Scope
Names are available from the point where they are declared until the end of the scope in which the declarations appears. For example, names defined in for-statement can only used in that statement.
Reference
A reference is not a object, it‘s just another name for an already existing object.Use ‘&‘.
Because references are not objects, we may not define a reference to a reference.
原文：https://www.cnblogs.com/bntodo/p/c-primer-study-notes.html