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--- function-macro [February 17, 2026 at 21:49] – yanevskiv
+++ function-macro [May 14, 2026 at 11:38] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
+# Function macro
+Function macro is a C preprocessor macro that looks like a function call when you use it.
+This is a basic example with a single expression. `sqr(x)` looks and feels like a function even though it's a macro. A good habit to get into is to always enclose arguments into parenthesis when you define function macros. For example, `#define sqr(x) x * x` would not behave like you would expect:  `sqr(2 + 3)` would expand into `2 + 3 * 2 + 3` which results in 11, not 25. By enclosing the arguments in parenthesis you guarantee precedence `((2 + 3) * (2 + 3))`.
+```c
+// Compile: gcc main.c -o program
+// Run:     ./program
+// Output:  Square of five is 25
+#include <stdio.h>
+#define sqr(x) ((x) * (x))
+int main()
+{
+    printf("Square of five is %d\n",  sqr(2 + 3));
+}
+```
+If want to make multiple statements in a function macro, a good way is to use `do { ... } while (0)`. This way, you gotta use ';' like you do when you call an actual function. Just remember to use '\' to extend the macro across multiple lines!
+```c
+// Compile: gcc main.c -o program
+// Run:     ./program
+// Output:  Square of '2 + 3' is 25!
+#include <stdio.h>
+#define sqr_calc(expr) do {                               \
+        int result = ((expr) * (expr));                   \
+        printf("Square of '" #expr "' is %d! ", result);  \
+        if (result % 2 == 0) {                            \
+            printf("%d is an odd number", result);        \
+        } else {                                          \
+            printf("%d is an even number", result);       \
+        }                                                 \
+    } while (0)
+int main()
+{
+    do_calc_sqr(2 + 3);
+}
+```
+## Links
+ - https://stackoverflow.com/questions/15575485/function-like-macros-in-c
+ - https://www.geeksforgeeks.org/cpp/macros-vs-functions/