A working version is ready

netcalc.php

@@ -1,23 +1,51 @@
 <?php
+$version="0.1";
 
-if (isset($argv[1]))
+function print_usage()
 {
-    //$value=$argv[1];
-    $value=$argv[1];
-    if ($value < 0 || $value > 32)
-    {
-        print "Please enter an integer between 0 and 32 only\n";
-        exit;
-    }
-    $base=32-$value;
-    $netsize=pow(2, $base);
-    $hosts=$netsize-2;
-    print "$hosts\n";
+    print "netcalc.php $GLOBALS[version]\n";
+    print "Jack-Benny Persson <jack-benny@cyberinfo.se>\n";
+    print "\n";
+    print "Usage: php netcalc.php <netmask>\n";
+    print "Example: php netcalc.php 24\n";
 }
 
-else
+// Check if first argument is set and and if not, print usage
+if (!isset($argv[1]))
 {
-    print "Enter something\n";
+    print_usage();
+    exit(1);
 }
 
+$value=$argv[1];
+
+// Check if our argument was a numeric value or not
+if (!is_numeric($value)) 
+{
+    print "Please enter numbers only (between 0 and 32)\n";
+    exit(1);
+}
+
+// Check if the value is between 0 and 32
+if ($value < 0 || $value > 32)
+{
+    print "Please enter an integer between 0 and 32 only\n";
+    exit(1);
+}
+
+// Calculate the diffrent values
+$base=32-$value;
+$netsize=pow(2, $base);
+$hosts=$netsize-2;
+if ($hosts < 0)
+{
+    $hosts = 0;
+}
+
+// And now, finally, print the values
+print "Netmask: $value\n";
+print "Total number of addresses: $netsize\n";
+print "Number of usable addresses for hosts: $hosts\n";
+exit(0);
+
 ?>