Added book examples

C19/define_example.c

@@ -0,0 +1,18 @@
+#define UP 1
+#define DOWN 2
+
+int main()
+{
+    int i = 1;
+    
+    if (i == UP )
+    {
+        // Do something
+    }
+    
+    if ( i == DOWN)
+    {
+        // Doe something else
+    }
+    return 0;
+}