Preprocessor Macros

Preprocessor Macros

The C preprocessor runs before compilation, performing text substitution. Lines starting with # are preprocessor directives.

Simple Constants

#define creates named constants -- the preprocessor replaces every occurrence with the value:

#define PI 3
#define MAX_SIZE 100

int arr[MAX_SIZE];

Standing orders: defined before the mission begins, automatically applied everywhere they're referenced. That's a #define.

Macros with Parameters

Macros can take arguments, acting like inline functions:

#define SQUARE(x) ((x) * (x))
#define MAX(a, b) ((a) > (b) ? (a) : (b))
#define MIN(a, b) ((a) < (b) ? (a) : (b))

printf("%d\n", SQUARE(5));   // 25
printf("%d\n", MAX(10, 20)); // 20

Why the Extra Parentheses?

Without parentheses, macros can produce unexpected results due to operator precedence:

#define BAD_SQUARE(x) x * x
printf("%d\n", BAD_SQUARE(2 + 3));
// Expands to: 2 + 3 * 2 + 3 = 11 (not 25!)

#define GOOD_SQUARE(x) ((x) * (x))
printf("%d\n", GOOD_SQUARE(2 + 3));
// Expands to: ((2 + 3) * (2 + 3)) = 25

Conditional Compilation

#define DEBUG 1

#if DEBUG
    printf("Debug mode\n");
#endif

Your Task

Define the following macros:

• ABS(x) -- absolute value of x
• CLAMP(x, lo, hi) -- clamp x between lo and hi

Print ABS(-5), ABS(3), CLAMP(15, 0, 10), and CLAMP(-3, 0, 10).