diff --git a/helloworld1.php b/helloworld1.php
index 5af7fc2..ed30d34 100644
--- a/helloworld1.php
+++ b/helloworld1.php
@@ -12,4 +12,4 @@
             <?php } ?>
         </ul>
     </body>
-</html>
\ No newline at end of file
+</html>
diff --git a/helloworld2.php b/helloworld2.php
index ede1aa7..8245f09 100644
--- a/helloworld2.php
+++ b/helloworld2.php
@@ -1,3 +1,12 @@
+<?php
+if (isset($_GET["nb"])) {
+    $nb = (int)$_GET["nb"];
+    if ($nb < 0 and $nb > 100)
+        $nb = null;
+} else
+    $nb = null;
+?>
+
 <!DOCTYPE html>
 <html lang="en">
     <head>
@@ -7,9 +16,7 @@
     <body>
         <ul>
             <?php
-            if (isset($_GET["nb"])) {
-                $nb = (int) $_GET["nb"];
-                if ($nb >= 0 and $nb <= 100)
+            if ($nb !== null) {
                 for ($i = 0; $i < $nb; $i++) { ?>
                     <li>Hello World !</li>
                 <?php }
@@ -18,4 +25,4 @@
             <?php } ?>
         </ul>
     </body>
-</html>
\ No newline at end of file
+</html>
diff --git a/helloworld3.php b/helloworld3.php
index 1182084..978afae 100644
--- a/helloworld3.php
+++ b/helloworld3.php
@@ -1,3 +1,18 @@
+<?php
+$nb = null;
+$name = null;
+$error = false;
+if (isset($_GET["nb"]) AND isset($_GET["name"])) {
+    $nb = (int)$_GET["nb"];
+    $name = htmlspecialchars($_GET["name"]);
+    if ($nb < 0 or $nb > 100) {
+        $error = true;
+        $nb = null;
+        $name = null;
+    }
+}
+?>
+
 <!DOCTYPE html>
 <html lang="en">
     <head>
@@ -5,14 +20,6 @@
         <title>Hello World 3</title>
     </head>
     <body>
-        <?php
-        $nb = 0;
-        $name = "";
-        if (isset($_GET["nb"]) AND isset($_GET["name"])) {
-            $nb = (int)$_GET["nb"];
-            $name = htmlspecialchars($_GET["name"]);
-        }
-        ?>
         <form>
             <label for="nb">Number: </label>
             <input id="nb" type="number" name="nb" min="0" max="100" value="<?= $nb ?>" required>
@@ -21,17 +28,17 @@
             <input type="submit" value="Send">
         </form>
 
+        <?php
+        if ($error) { ?>
+        <strong>Invalid args !</strong>
+        <?php } ?>
+
         <ul>
-            <?php
-            if ($nb AND $name) {
-                if ($nb >= 0 and $nb <= 100)
-                    for ($i = 0; $i < $nb; $i++) { ?>
-                        <li>Hello <?= $name ?> !</li>
-                    <?php }
-                else { ?>
-                    <strong>Invalid args !</strong>
+             <?php if ($nb !== null AND $name !== null) {
+                for ($i = 0; $i < $nb; $i++) { ?>
+                    <li>Hello <?= $name ?> !</li>
                 <?php }
-            } ?>
+             }?>
         </ul>
     </body>
-</html>
\ No newline at end of file
+</html>
diff --git a/helloworld4.php b/helloworld4.php
index 2fd8344..745c6fe 100644
--- a/helloworld4.php
+++ b/helloworld4.php
@@ -1,3 +1,39 @@
+<?php
+$children = 0;
+$married = false;
+$income = 0;
+if (isset($_POST["children"]) AND isset($_POST["income"])) {
+    $children = (int)$_POST["children"];
+    if (isset($_POST["married"]))
+        $married = (bool)$_POST["married"];
+    else
+        $married = false;
+    $income = (float)$_POST["income"];
+}
+
+if ($married)
+    $n = 2+$children/2;
+else
+    $n = 1+$children/2;
+
+$q = $income/$n;
+
+$t = 0;
+if ($q >= 0 AND $q <= 9963)
+    $t =  $income*0 - 0*$n;
+elseif ($q <= 27518)
+    $t = $income*0.14 - 1394.96*$n;
+elseif ($q <= 73778)
+    $t = $income*0.3 - 5798*$n;
+elseif ($q <= 156243)
+    $t = $income*0.41 - 13913.69*$n;
+elseif ($q >= 156244)
+    $t = $income*0.45 - 20163.45*$n;
+
+$t = round($t);
+echo $q;
+?>
+
 <!DOCTYPE html>
 <html lang="en">
     <head>
@@ -5,20 +41,7 @@
         <title>Hello World 4</title>
     </head>
     <body>
-        <?php
-            $children = 0;
-            $married = false;
-            $income = 0;
-            if (isset($_GET["children"]) AND isset($_GET["income"])) {
-                $children = (int)$_GET["children"];
-                if (isset($_GET["married"]))
-                    $married = (bool)$_GET["married"];
-                else
-                    $married = false;
-                $income = (float)$_GET["income"];
-            }
-        ?>
-        <form>
+        <form method="POST">
             <label for="children">Number of children: </label>
             <input id="children" type="number" name="children" min="0" value="<?= $children ?>" required> <br />
             <label for="married">Married: </label>
@@ -27,29 +50,7 @@
             <input id="income" type="number" name="income" min="0" step="any" value="<?= $income ?>" required> <br />
             <input type="submit" value="Send">
         </form>
-        <?php
-            if ($married)
-                $n = 2+$children/2;
-            else
-                $n = 1+$children/2;
 
-            $q = $income/$n;
-
-            $t = 0;
-            if ($q >= 0 AND $q <= 9963)
-                $t =  $income*0 - 0*$n;
-            elseif ($q >= 9964 AND $q <= 27518)
-                $t = $income*0.14 - 1394.96*$n;
-            elseif ($q >= 27519 AND $q <= 73778)
-                $t = $income*0.3 - 5798*$n;
-            elseif ($q >= 73779 AND $q <= 156243)
-                $t = $income*0.41 - 13913.69*$n;
-            elseif ($q >= 156244)
-                $t = $income*0.45 - 20163.45*$n;
-
-            $t = round($t);
-
-            ?>
         <p>Your taxes is <?= $t ?></p>
     </body>
-</html>
\ No newline at end of file
+</html>
