diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index e04ff992b09515a2a7c41ae8bf0228383741483d..1e17a78d53f1c7f8925bf8c95d734755905ba0f6 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -11,7 +11,24 @@ syscall_init (void)
 {
   intr_register_int (0x30, 3, INTR_ON, syscall_handler, "syscall");
 }
+/* from lib/syscall-nr.h 
+system calls numbers are 
+    SYS_HALT,                  0
+    SYS_EXIT,                  1
+    SYS_EXEC,                  2 
+    SYS_WAIT,                  3 
+    SYS_CREATE,                4
+    SYS_REMOVE,                5
+    SYS_OPEN,                  6
+    SYS_FILESIZE,              7
+    SYS_READ,                  8
+    SYS_WRITE,                 9
+    SYS_SEEK,                  10
+    SYS_TELL,                  11
+    SYS_CLOSE,                 12
 
+these are used for the case instead of number
+*/
 
 static void
 syscall_handler (struct intr_frame *f UNUSED)
@@ -24,5 +41,27 @@ syscall_handler (struct intr_frame *f UNUSED)
       shutdown_power_off();
 		  break;
     }
+    /*
+    // each team member should select on syscall.
+    // develop one from the cw document
+
+
+    case SYS_EXIT:{
+      //to be developed
+      break;
+    }
+    case SYS_EXEC:{
+      //to be developed
+      break;
+    }
+    case SYS_WAIT:{
+      //to be developed
+      break;
+    }
+    case SYS_WAIT:{
+      //to be developed
+      break;
+    }
+    */
   thread_exit ();
 }