Arg error checking

hex.c

@@ -1,6 +1,7 @@
 #include <stdio.h>
 
-// TODO: Error checking
+// TODO: ASCII/Position printing 
+// TODO: Stop appending garbage at file end
 
 #define BYTES 1024
 #define BYTES_PER_LINE 10
@@ -18,8 +19,14 @@ void print_hex(unsigned char* buf, int byteno)
   puts("");
 }
 
-void main(int argc, char** argv)
+int main(int argc, char** argv)
 {
+  if (argc != 2)
+  {
+    printf("Usage: %s <file>\n", argv[0]);
+    return -1;
+  }
+
   FILE* f = fopen(argv[1], "r");
   unsigned char buf[BYTES];
   int byteno = fread(buf, 1, BYTES, f);
@@ -30,14 +37,27 @@ void main(int argc, char** argv)
     char cmd;
     int loc;
     scanf("%c%d", &cmd, &loc);
-
-    if (cmd == 'p') print_hex(buf + loc, BYTES_PER_LINE);
-    if (cmd == 'e') scanf("%x", buf + loc);
-    if (cmd == 's') break;
+    switch(cmd)
+    {
+      case 'p':
+      case 'P':
+        print_hex(buf + loc, BYTES_PER_LINE);
+        break;
+      case 'e':
+      case 'E':
+        scanf("%hhx", buf + loc);
+        break;
+      case 's':
+      case 'S':
+        fclose(f);
+        f = fopen(argv[1], "w");
+        fwrite(buf, 1, BYTES, f);
+        fclose(f);
+        break;
+      case 'q':
+      case 'Q':
+        return 0;
+        break;
+    }
   }
-
-  fclose(f);
-  f = fopen(argv[1], "w");
-  fwrite(buf, 1, BYTES, f);
-  fclose(f);
 }