Or the blank question in the morning

The problem is that, for example, if you do not input anything in the input box, click submit and click it to print out "You haven't input yet". However, what I printed out is "NONE". I listened to others. I just want to change isset to trim. When I try to submit it empty, I can print "You haven't entered it "...

The problem is that, for example, if you do not input anything in the input box, click submit and click it to print out "You haven't input yet". However, what I printed out is "NONE". I listened to others. I just changed isset to trim. I tried to print out "You haven't input" when I open the empty commit, but the problem is that every time I open this page, I will report the error Notice: undefined index: num in D: wampwwwtest. why does php on line 13 look like this?
I tried to change it to empty. What should I do? What's more, the result I want is that when I open this page, No prompts are displayed, "no" or "You have not entered". Thank you.

      
      
  Prepare ("select * from aaa where num =? "); $ Stmt-> execute (array ($ _ POST ['num']); $ res = $ stmt-> fetchall (PDO: FETCH_ASSOC ); if ($ res) {foreach ($ res as $ v) {echo $ v ['name'] ;}} else {echo "no ";}} else {echo "You have not entered" ;}?>

Reply content:

The problem is that, for example, if you do not input anything in the input box, click submit and click it to print out "You haven't input yet". However, what I printed out is "NONE". I listened to others. I just changed isset to trim. I tried to print out "You haven't input" when I open the empty commit, but the problem is that every time I open this page, I will report the error Notice: undefined index: num in D: wampwwwtest. why does php on line 13 look like this?
I tried to change it to empty. What should I do? What's more, the result I want is that when I open this page, No prompts are displayed, "no" or "You have not entered". Thank you.

      
      
  Prepare ("select * from aaa where num =? "); $ Stmt-> execute (array ($ _ POST ['num']); $ res = $ stmt-> fetchall (PDO: FETCH_ASSOC ); if ($ res) {foreach ($ res as $ v) {echo $ v ['name'] ;}} else {echo "no ";}} else {echo "You have not entered" ;}?>

Because the POST data does not exist before you submit it, the error $ _ POST ['num'] does not exist. Just add @ to the front, or define POST as null first.

Different PHP versions cause different error levels. You can hide notice-level errors at the top entry:

error_reporting( error_reporting() & ~E_NOTICE )

I can't see it anymore.

If (empty ($ _ POST ['num']) {echo 'num not input ';}