How to express constants in c language

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: Constants declared using const can be accessed while the program is running , and constants defined by #define are only replaced at compile time.
• Type: const Declared constants have an explicit type, while #define defined constants have a type determined by the replaced value.
• Modability: const The declared constant cannot be modified, while the #define defined constant can be modified by redefining it.

Usage Guide

• For values ​​that will not change, it is recommended to use const to declare constants.
• For values ​​that need to be replaced at compile time, you can use #define to define constants.
• To avoid name conflicts, use uppercase letters and underscores when defining constants using #define.

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