Salut a tous
je ne comprend pas cette erreur (ci desous) ou alors quelle erreur est ce que je fais au niveau du else{}

PHP Notice: Undefined variable: idCat in C:\\xampp\\htdocs\\kant\\produits.php on line 127, referer: http://localhost/kantt/index.php?panier=1

<?php

require_once("connection.php");



if (isset($_POST["motCle"])){

	$motCle = $_POST["motCle"];
	$req = $dbConnect->query("SELECT * FROM produit WHERE designation LIKE '%$motCle%'");

}

elseif (isset($_GET["idCat"])) {

	$idCat = $_GET["idCat"];
	
	$req = $dbConnect->query("SELECT * FROM produit WHERE code_cat='$idCat'");
   
}


else{
    
	$req = $dbConnect->query("SELECT * FROM produit");
}


?>

<div id="produits">

<?php

while($prod=$req->fetch(PDO::FETCH_ASSOC)) {

?>

	<div id="produit" align="center">
	
		<form method="post" action="formular.php">
		<table>

				<td><a>Pos.Nr. / Kantt-Nr.</a></td>
				<td><input type="text" name="postnr_kanttnr" size="60" required="required"></td>

			</tr>

			<tr>

				<td><a>Bezeichnung:</a></td>
				<td><input type="text" name="bezeichnung" size="60" required="required"></td>

			</tr>

			<tr>

				<td><a>Farbe:</a></td>
				<td><input type="text" name="farbe" size="60" required="required"></td>

			</tr>

			<tr>
				<td><a>Anzahl x Länge:</a></td>
				<td><input type="text" name="anzahl_laenge" size="60" required="required"></td>

			</tr>

			<tr>
				<td><a>Bemerkung:</a></td>
				<td><input type="text" name="bemerkung" size="60" required="required"></td>

			</tr>

			
			<tr>
				<td></td>
				<td rowspan="1" align="center"><img src="images/<?php echo $prod['photo']?>"></td>

			</tr>

			

			<tr>

				<td><h3>Designation:</h3></td><td width="100px"><h3><?php echo $prod['DESIGNATION']?></h3></td>

			</tr>
         

			<tr>	
				<td><a>a</a><input type="text" name="a" size="4"  required="required" ></td>				               
				<td><a>b</a><input type="text" name="b" size="4"  required="required"></td>
			</tr>
		
		    <tr>
				<td><a>c</a><input type="text" name="c" size="4"  required="required"></td>				
                <td><a>d</a><input type="text" name="d" size="4"  required="required"></td>
			</tr>

			<tr>
				<td><a>e</a><input type="text" name="e" size="4" required="required"></td>
				<td><a>f </a><input type="text" name="f" size="4" required="required"></td>
			</tr>
			
			<tr>	
				<td><a>g</a><input type="text" name="g" size="4" required="required"></td>				
				<td><a>α</a><input type="text" name="alpha" size="4" required="required"></td>
			</tr>
		
			<tr>
				<td colspan="4" align="right">
					<div id="formPanier">
						<form method="post" action="addCaddie.php" id="form2">
						     
							<input type="text" name="quantite" size="4" value="1"/>
							
						
							
							<input type="hidden" name="designation" value="<?php echo $prod['DESIGNATION']; ?>" />
							
						
							<input type="image" src="images/korb.jpg" value="submit" align="right"/>
							</tr>
						</form>
					</div>
					<input type="hidden" name="idCat" value="<?php echo $idCat; ?>">   //c'est ici la ligne 127
				</td>
			</tr>
			<tr>

				<td></td><td align="right"><br><input type="submit" name="produit_erstellen" value="Speichern"></td>

			</tr>
		</table>

		
		</form>
	</div>
<?php

}

?>

</div>

salut,

cela signifie qu'a la ligne 127 tu utilises une variable $idCat qui n'existe pas.
Dans ce genre de cas il faut faire confiance à ce que te dit php

C'est le tant que tu n'entres pas de le elsif ligne 14 (donc soit $_POST["motCle"] existe, soit $_GET["idCat"] n'existe pas

dans ton cas utilise plutôt l'information qui vient de la requête sql

ton code pourrait ressembler à ceci

<?php
require_once 'connection.php';
$sql = 'select * from produit where 1=1';
if (isset($_POST['motCle'])) {
    $sql .= ' and designation LIKE '.$dbConnect->quote('%'.$_POST['motCle'].'%');
}
if (isset($_GET['idCat'])) {
    $sql .= 'and code_cat='.$dbConnect->quote($_GET['idCat']);
}
$req = $dbConnect->query($sql);
?>
<div id="produits">
<?php
while ($prod = $req->fetch(PDO::FETCH_ASSOC)) {
    ?>
  <div id="produit" align="center">
    <form method="post" action="formular.php">
    <table>
        <td><a>Pos.Nr. / Kantt-Nr.</a></td>
        <td><input type="text" name="postnr_kanttnr" size="60" required="required"></td>
      </tr>
      <tr>
        <td><a>Bezeichnung:</a></td>
        <td><input type="text" name="bezeichnung" size="60" required="required"></td>
      </tr>
      <tr>
        <td><a>Farbe:</a></td>
        <td><input type="text" name="farbe" size="60" required="required"></td>
      </tr>
      <tr>
        <td><a>Anzahl x Länge:</a></td>
        <td><input type="text" name="anzahl_laenge" size="60" required="required"></td>
      </tr>
      <tr>
        <td><a>Bemerkung:</a></td>
        <td><input type="text" name="bemerkung" size="60" required="required"></td>
      </tr>
      <tr>
        <td></td>
        <td rowspan="1" align="center"><img src="images/<?php echo $prod['photo']?>"></td>
      </tr>
      <tr>
        <td><h3>Designation:</h3></td><td width="100px"><h3><?php echo $prod['DESIGNATION']?></h3></td>
      </tr>
      <tr>
        <td><a>a</a><input type="text" name="a" size="4"  required="required" ></td>
        <td><a>b</a><input type="text" name="b" size="4"  required="required"></td>
      </tr>
      <tr>
        <td><a>c</a><input type="text" name="c" size="4"  required="required"></td>
        <td><a>d</a><input type="text" name="d" size="4"  required="required"></td>
      </tr>
      <tr>
        <td><a>e</a><input type="text" name="e" size="4" required="required"></td>
        <td><a>f </a><input type="text" name="f" size="4" required="required"></td>
      </tr>
      <tr>
        <td><a>g</a><input type="text" name="g" size="4" required="required"></td>
        <td><a>?</a><input type="text" name="alpha" size="4" required="required"></td>
      </tr>
      <tr>
        <td colspan="4" align="right">
          <div id="formPanier">
            <form method="post" action="addCaddie.php" id="form2">
              <input type="text" name="quantite" size="4" value="1"/>
              <input type="hidden" name="designation" value="<?php echo $prod['DESIGNATION']; ?>" />
              <input type="image" src="images/korb.jpg" value="submit" align="right"/>
              </tr>
            </form>
          </div>
          <input type="hidden" name="idCat" value="<?php echo $PROD['code_cat']; ?>">
        </td>
      </tr>
      <tr>
        <td></td>
        <td align="right"><br><input type="submit" name="produit_erstellen" value="Speichern"></td>
      </tr>
    </table>
    </form>
  </div>
<?php
}
?>
</div>

@+

ps : pense à mettre un titre parlant pour tous "erreur" ça ne veux rien dire

Merci bien