parameter error handling, return 1 on error

minebash

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-#TODO: highscore, monochrome, flags red if too many
+#TODO: highscore, monochrome, flags red if too many, adventure mode
 import random, io, sys, time, os
 
 import curses
@@ -34,7 +34,7 @@ clWhite, clRed, clCyan, clBlue, clYellow, clGreen, clInverted = None, None, None
 difficulty = 'medium'
 
 param_error = 'minebash: Invalid parameters. See \'minebash help\' for help '
-helpstr = '''Usage: minebash [easy|medium|hard] [width height minecount]
+helpstr = '''Usage: minebash [easy|medium|hard] | [width height minecount]
     
 Difficulty presets:
     easy:    5x5  4 mines
@@ -69,20 +69,24 @@ if len(sys.argv) > 1:
             MINECOUNT = 35
         else:
             print(param_error)
-            sys.exit(0)
+            sys.exit(1)
         difficulty = sys.argv[1] 
     elif len(sys.argv) == 4: #this means the user has specified width, height and minecount
-        width = int(sys.argv[1])
-        height = int(sys.argv[2])
+        try:
+            width = int(sys.argv[1])
+            height = int(sys.argv[2])
+        except ValueError:
+            print(param_error)
+            sys.exit(1)
         if int(sys.argv[3]) < width*height:
             MINECOUNT = int(sys.argv[3])
             difficulty = 'custom'
         else:
             print('Minecount muss be less than width x height.')
-            system.exit(0)
+            sys.exit(1)
     else:
         print(param_error)
-        sys.exit(0)
+        sys.exit(1)
 playfield = [[UNKNOWN for x in range(width)] for y in range(height)]
 
 headline = '┌'