Added book examples

C20/macro_function_example.c

@@ -0,0 +1,8 @@
+#include <stdio.h>  
+#define MIN(a,b) ((a)<(b)?(a):(b))  
+
+int main(void) 
+{  
+   printf("The minimum value of 10 and 20 is: %d\n", MIN(10,20));    
+   return 0;
+}