PHP using if and set new string [closed]

I'm using form HTML that I post variable 'DDD' between '11' and '99'. I want to get the value sent by user and set a new string. For example:

My PHP code to get user POST is:

$sDDDs = $_POST['DDDs'];

I have two groups:

• Group1: 1x4x5x6x
• Group2: 2x3x7x8x9x

So the user sent 11 I need to set the value of the variable $sDDDs as '1x4x5x6x' if the user sent 75 then I set the variable $sDDDs as '2x3x7x8x9x'. I need this because in my code i'm using case and I execute the page based by chouses from user.

I trying to use IF statement but I don't get, I don't know if I can use this filter in my Switch -> Case

Follow the code of my switch case:

case($sIdProduct=='ProductName' and $sAnoMes=='DateUser' and $sDDDs=='1x4x5x6x'):