Added book examples

C20/conditional_directive_example.c

@@ -0,0 +1,15 @@
+#include <stdio.h>  
+#include <conio.h>  
+
+#define DEBUG_ON 1  
+
+int main(void) 
+{  
+#if DEBUG_ON == 1
+	printf("Debug mode - about to do something\n");  
+#else  
+	print("Running in standard mode");  
+#endif  
+	
+	return 0;
+}

C20/formatting_directive_example.c

@@ -0,0 +1,15 @@
+#include <stdio.h>  
+#include <conio.h>  
+
+#define DEBUG_ON 1  
+
+int main(void) 
+{  
+#ifdef DEBUG_ON 
+	printf("Debug mode - about to do something\n");  
+#else  
+	print("Running in standard mode");  
+#endif         
+
+return 0;
+} 

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;
+}