Added error exit on wrong command and prepared waitfg

tsh.c

@@ -168,22 +168,24 @@ void eval(char *cmdline)
   char *argv[MAXARGS]; // Save flags for process
   int bg = parseline(cmdline, argv); // See whether cmd is back or foreground and parse cmdline
   struct job_t *job;
+
+  if (argv[0] != NULL) { // Do nothing, but don't crash on empty line
     if (!builtin_cmd(argv)) { // if cmdline is not a builtin
       int pid = fork(); // fork process
       if (pid == 0) { // Child Process
         if (execve(argv[0], argv, environ) != 0) { // if exec failed
-        printf("Command not found.\n");
-        exit(0);
+          printf("%s Command not found.\n", argv[0]);
+          exit(1);
         }
-      exit(0);
       } else { // Parent Process
         wait(NULL);
+        addjob(jobs, pid, bg ? BG : FG, cmdline);
         if (bg) {
-        addjob(jobs, pid, BG, cmdline);
           job = getjobpid(jobs, pid);
           printf("[%d] (%d) %s", job->jid, pid, cmdline);
         } else {
-        addjob(jobs, pid, FG, cmdline);
+          // waitfg(pid);
+        }
       }
     }
   }
@@ -298,9 +300,9 @@ void do_bgfg(char **argv)
  */
 void waitfg(pid_t pid)
 {
-  // while (pid == fgpid(jobs)) {
-  //   sleep(1);
-  // }
+  while (pid == fgpid(jobs)) {
+    sleep(1);
+  }
   return;
 }