diff --git a/Makefile b/Makefile
index e42377f..a9b3531 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,6 @@
 subnetcalc: subnetcalc.c
-	gcc -Wall -pedantic subnetcalc.c -lm -static -o subnetcalc
+	gcc -std=c99 -Wall -pedantic subnetcalc.c -lm -static -o subnetcalc
 	docker build . -t subnetcalc
 
 clean: subnetcalc
 	rm subnetcalc
-	docker image rm subnetcalc
diff --git a/subnetcalc b/subnetcalc
index 80a20ad..6c8d5e7 100755
Binary files a/subnetcalc and b/subnetcalc differ
diff --git a/subnetcalc.c b/subnetcalc.c
index 68135c9..61623cc 100644
--- a/subnetcalc.c
+++ b/subnetcalc.c
@@ -9,26 +9,26 @@
 int main(void)
 {
     int net;
-    double hosts;
-    double addr;
+    long int hosts, addr;
     printf("Enter netmask in slash-notation without the slash: ");
     scanf("%2d", &net);
 
-    if (net >= 0 && net <= 32) // Sanity check the user input
+    if (net >= 0 && net <= 32) /* Sanity check the user input */
     {
         printf("Netmask bit: %d\n\n", net);	
-        addr = pow(2, 32-net); // Calculate number of addresses
-        printf("%.0lf total addresses\n", addr);
+        addr = pow(2, 32-net); /* Calculate number of addresses */
+        printf("%ld total addresses\n", addr);
 
-        hosts = addr-2; 
-        if (hosts < 0)   // Check if number of usable hosts is a negative value
+        hosts = addr-2;
+        /* Check if number of usable hosts is a negative value */ 
+        if (hosts < 0)
         {
-            hosts = 0;   // Set usable hosts to zero if it was negative
+            hosts = 0;   /* Set usable hosts to zero if it was negative */
         }   
-        printf("%.0lf usable addresses for hosts\n", hosts);
+        printf("%ld usable addresses for hosts\n", hosts);
         return 0;
     }
-    else  // If the user entered anything else than 0-32
+    else  /* If the user entered anything else than 0-32 */
     {
         printf("Only values between 0-32 are accepted\n");
         return 1;