Adding PHP examples

03_recursion/php/01_countdown.php

@@ -0,0 +1,14 @@
+<?php
+
+function countdown($i)
+{
+    echo $i;
+    // base case
+    if ($i <= 0) {
+        return;
+    } else {
+        countdown($i - 1);
+    }
+}
+
+countdown(5);

03_recursion/php/02_greet.php

@@ -0,0 +1,21 @@
+<?php
+
+function greet2($name)
+{
+    echo 'how are you, ' . $name . '?';
+}
+
+function bye()
+{
+    echo 'ok bye!';
+}
+
+function greet($name)
+{
+    echo 'hello, ' . $name . '!';
+    greet2($name);
+    echo  'getting ready to say bye...';
+    bye();
+}
+
+greet('adit');

03_recursion/php/03_factorial.php

@@ -0,0 +1,11 @@
+<?php
+
+function fact($x)
+{
+    if ($x === 1) {
+        return 1;
+    }
+    return $x * fact($x - 1);
+}
+
+echo fact(5);