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.