diff --git a/02-vars-and-math.c b/02-vars-and-math.c
index 2a881f6..16df37f 100644
--- a/02-vars-and-math.c
+++ b/02-vars-and-math.c
@@ -1,11 +1,15 @@
 #include <stdio.h>
 
+#define  LOWER  0
+#define  UPPER  300
+#define  STEP   20
+
 /* print Fahrenheit-Celsius table */
 int main()
 {
 	int fahr;
 
 	printf("Fahrenheit\tCelsius\n=======================\n");
-	for (fahr = 300; fahr >= 0; fahr = fahr - 20)
+	for (fahr = UPPER; fahr >= LOWER; fahr = fahr - STEP)
 		printf("%3d\t\t%7.1f\n", fahr, (5.0/9.0)*(fahr-32));
 }
diff --git a/03-celsius-to-fahrenheit.c b/03-celsius-to-fahrenheit.c
index 85e9b7a..96c2164 100644
--- a/03-celsius-to-fahrenheit.c
+++ b/03-celsius-to-fahrenheit.c
@@ -1,11 +1,15 @@
 #include <stdio.h>
 
+#define  LOWER  0
+#define  UPPER  300
+#define  STEP   20
+
 /* print Celsius-Fahrenheit table */
 int main()
 {
 	int cels;
 
 	printf("Celsius\t\tFahrenheit\n==========================\n");
-	for (cels = 0; cels <= 300; cels = cels + 20)
+	for (cels = LOWER; cels <= UPPER; cels = cels + STEP)
 		printf("%3d\t\t%10.0f\n", cels, (9.0/5.0)*cels+32);
 }