Data, the numbers and characters that bear the information you use.

An expression is a bit of PHP that can be evaluated to produce a value.

The simplest yet most accurate way to define an expression is "anything that has a value".

Operators are combined with values to produce expressions, and every C expression has a value.

A statement is a complete instruction to the computer..

A statement can be an assignment, a function call, a loop, a conditional statement or even a statement that does nothing (an empty statement).

再次思考这些句子，感觉很棒。

Make me feel something.

A pointer points to the location of a variable or other data object. The & prefix used with the scanf() function creates a pointer telling scanf() where to place information.