define usage of function macro

define definition function macro usage: 1. Define a simple calculation macro, "#define SQUARE(x) ((x) * (x))"; 2. Define a macro with multiple parameters, "#define MAX(a, b) ((a) > (b) ? (a) : (b))"; 3. Define macros with complex expressions, "#define ABS(x) ((x ) ea7660032eb04c051a645ad22556e13e (10) ? (5) : (10))`, that is, `10`.

3. Define macros with complex expressions:

#define ABS(x) ((x) < 0 ? -(x) : (x))

When using `ABS(-5)` in your code, the preprocessor will replace it with `((-5 ) < 0 ? -(-5) : (-5))`, that is, `5`.

It should be noted that function macros are just simple text replacement, without type checking and scope restrictions. Therefore, care needs to be taken when using function macros to avoid potential errors and side effects. In addition, since the function macro is replaced during the preprocessing stage, its parameters are not evaluated multiple times. Therefore, expressions with side effects should be avoided in function macros.

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