Add values to an array while looping through [duplicate]

I am looking for a way to add values to an array while I am looping through. This might sound a bit confusing but the following example will show what I want to do.

// Create a test array
$rows = range('a', 'z');

// Loop through the test array
foreach ($rows as $key => $row) {
    print $key . ': '.$row."\n";
    if (false === strpos($key, 'added') && $row == 'd') {
        // Add value to test array
        $rows['added_'.$key] = $row;
    }
}

Output

0: a
1: b
2: c
3: d
4: e
5: f
6: g
7: h
8: i
9: j
10: k
11: l
12: m
13: n
14: o
15: p
16: q
17: r
18: s
19: t
20: u
21: v
22: w
23: x
24: y
25: z

However, the foreach loop will not output the added values.