How to use define in c language

The define directive of C language is used to define macros to achieve code reuse and maintainability. Its usage is: #define macro name value. Advantages include: defining constants, simplifying code, and improving maintainability. Notes include: macro names cannot start with numbers or underscores. Macros are expanded during the preprocessing stage. Macros should be used with caution.

Usage of define in C language

#define is a preprocessing instruction in C language, mainly used for definition Macro. Macros are replaced with given values ​​at compile time, allowing code reuse and maintainability.

Usage:

<code class="c">#define 宏名 值</code>

For example:

<code class="c">#define PI 3.14</code>

The above code defines the PI macro as a constant 3.14.

Function:

• Define constants: define can define immutable constants, similar to the const keyword, but in preprocessing stage processing.
• Code simplification: The code can be simplified by using macros to avoid repeatedly writing the same values ​​or complex expressions.
• Maintainability: If you need to change a constant, you only need to modify the define statement, not everywhere it is used.

Note:

• The first character of the macro name cannot be a number or underscore.
• Values ​​can be literals, constants, or expressions.
• Macros are expanded during the preprocessing phase and therefore cannot contain function calls or other expressions that require runtime.
• Macros should be used with caution as they may cause compiler errors or difficult-to-understand code.

Example:

<code class="c">#define MAX_SIZE 100

int main() {
    int arr[MAX_SIZE];
    // ...
}</code>

In this example, the MAX_SIZE macro defines an integer array arr of size 100. Without define, you would need to use the number 100 multiple times throughout the program, which would make the code lengthy and difficult to maintain.

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