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In C language, the keyword const and the prefix operator #define are used to declare constants. Constants declared by const can be accessed when the program is running, have a clear type, and cannot be modified; while constants defined by #define can only be replaced at compile time, and the type is determined by the replaced value and can be modified. For values that need to be replaced at compile time, you can use #define to define constants; for values that will not change, it is recommended to use const to declare constants.
Representation method of constants in C language
In C language, constants represent values that do not change. There are two main ways to represent constants:
Using the keywords
Declaring constants using the const
keyword. The declaration of a constant variable is similar to that of an ordinary variable, but const
is added before the variable name. For example:
<code class="c">const int MAX_SIZE = 100; const char MESSAGE[] = "Hello, world!";</code>
Use the prefix operator
Use the prefix operator #define
to define constants. It replaces the symbol with the specified constant value at compile time. For example:
<code class="c">#define PI 3.14159 #define MAX_SPEED 100</code>
Difference
const
can be accessed while the program is running , and constants defined by #define
are only replaced at compile time. const
Declared constants have an explicit type, while #define
defined constants have a type determined by the replaced value. const
The declared constant cannot be modified, while the #define
defined constant can be modified by redefining it. Usage Guide
const
to declare constants. #define
to define constants. #define
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