i want to sum all digit in a number - php

Question

i want to add all digit in a number and if it is 11,22 then i want to display only 11 or 22 else i want to make it a single digit.
example 30=3+0=3
28=2+8=10=1+0=1
i just made a codebut it have an error
please help.
<?php
$day = 17;
$month = 8;
$year = 1993;
function sumday($day)
{
if ($day == 11)
{
$sday = 11;
}
elseif ($day == 22)
{
$sday = 22;
}
elseif ($day == 29)
{
$sday = 11;
}
else
{
do {
$nday = $day . "";
$sday = 0;
for ($i = 0; $i < strlen($nday); ++$i)
{
$sday += $nday[$i];
}
while ($sday <=9);
}
return $sday;
}

Answer 1

First of all I would suggest you to learn to separate the tasks that a function do.
You ask to sum up the digits of a number, you may first create a function called sum_digits
<?php
function sum_digits($num) {
if ($num < 10)
return $num;
return $num % 10 + sum_digits(floor($num/10));
}
and then via conditional do whatever you need to do.

Answer 2

please refer to unnikked's answer, that's a good answer.
And here's the full code, combined with unnikked's answer
<?php
$day = 17;
$month = 8;
$year = 1993;
function sumday($day)
{
if ($day == 11)
{
$sday = 11;
}
elseif ($day == 22)
{
$sday = 22;
}
elseif ($day == 29)
{
$sday = 11;
}
else{
$sday = $day;
do {
$sday = $sday % 10 + floor($sday/10);
} while ($sday >= 10);
}
return $sday;
}
?>
EDIT: If you want to return the sum if it's 11,22,33 in the while loop, then put the conditions in the while loop rather than using if else condition, it's much simpler tho :)
function sumday($day)
{
$sday = $day;
while ($sday >= 10 && $sday != 11 && $sday != 22 && $sday != 29){
$sday = $sday % 10 + floor($sday/10);
}
return $sday;
}
EDIT: here's the logic that can split the day and sum them
function sumday($day)
{
$sday = $day;
$arrday = str_split($sday); // split the day into array
$sumarrday = 0;
for($i = 0; $i < strlen((string)$sday); $i++){
$sumarrday = $sumarrday + $arrday[$i]; // sum the day from the array
}
$sday = $sumarrday;
// here you can modify the condition of while statement for your needs
// for example, if you want to return 29 when 29 shows up, add this to your condition, && $sday != 29
while ($sday >= 10){
$sday = $sday % 10 + floor($sday/10);
}
return $sday;
}

Answer 3

Try this:
else {
$nday = $day . ""; //moved out wrom loop
do {
$sday = 0;
for ($i = 0; $i < strlen($nday); ++$i)
{
$sday += $nday[$i];
}
$nday = $sday . ""; // you forget this line
while ($sday <=9);
}