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C language constant definition rules

The definition of constant: a constant is a quantity whose value cannot be changed while the program is running.

Constants in C language can be divided into direct constants and symbolic constants.

Direct constant refers to a form expressed directly by specific data, which can be divided into integer constant, real constant, character constant and string constant.

Symbolic constants refer to constants defined by C language identifiers.

Integer constants are integer constants, decimal, octal and hexadecimal numbers. For example, 10,012, 0x0A

Real constants are also called floating-point constants. Such as: 3.14, 1.2E-4

Character constants must be enclosed in single quotation marks. Such as:'M','\ n'

String constants are enclosed in double quotes. For example, "abc", "a"

Symbolic constants can be represented by macro definitions or by const keywords. For example: # define PI 3.14 const float PI = 3.14

Expansion of knowledge points:

In C, there are two simple ways to define constants:

1. Use # define preprocessor

two。 Use the const keyword

Const defines a variable, not a constant, but the value of this variable is not allowed to change is a constant! With a type. There is type checking at compile time.

Define defines constants without types and only makes simple character substitutions. It works during precompilation, and there is no type checking.

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