Question

$child= array();
$i = 0;

while($row = mysql_fetch_array($result, MYSQL_ASSOC))
{
    $child[i] = $row['userId'];
    $i++;
} 

$i = 0;
while($i<=5)
{
    echo $child[i];
    $i++;
}

It is printing same value.

Answer 1

You are using i for the array index instead of $i:

$child[i]

This should be $child[$i]. Because the i in $child[i] is interpreted as a constant (value of constant i is used as index) or if there is no such constant as string. You can get a variable/value dump with var_dump.