Incorrect syntax errors in sql server function. Please help.

Question

This is my sql server function:
create function dbo.CleanTheStringAdv (@theString nvar
char(500), @CleanMode as int) 
returns nvarchar(500)  
begin  
--define variables
declare @strAlphaNumeric nvarchar(500)  
declare @i int
declare @strChar nvarchar(500)
declare @CleanedString nvarchar(500)
--initiate values
set @CleanedString =''  
set @theString = @theString + ''
SET @i = 1
--Determine if we are looking for numeric values only or numbers and letters
return case @CleanMode
   WHEN 1
   THEN @strAlphaNumeric = '0123456789'
   WHEN 2
   THEN @strAlphaNumeric = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
   WHEN 3
   THEN @strAlphaNumeric = '|0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
   else 0
 end 
--Search through chars in the string passed to the function
    while (@i <= Len(@theString))
begin
@strChar = substring(@theString, @i, 1)
If (charindex(@strAlphaNumeric, @strChar) <>0)
--if the current char being reviewed is valid then add it to the new string
begin
@CleanedString = @CleanedString + @strChar
end
end
return @CleanedString
and below are the syntax errors I see when I press F5:
Msg 102, Level 15, State 1, Procedure CleanTheStringAdv, Line 24
Incorrect syntax near '='.
Msg 102, Level 15, State 1, Procedure CleanTheStringAdv, Line 39
Incorrect syntax near '@strChar'.
Msg 102, Level 15, State 1, Procedure CleanTheStringAdv, Line 43
Incorrect syntax near '@CleanedString'.
Any help is highly appreciated.....

Answer 1

Here is the full code for the function:
create function dbo.CleanTheStringAdv (@theString nvarchar(500), @CleanMode as int)
returns nvarchar(500)
as
begin
--define variables
declare @strAlphaNumeric nvarchar(500)
declare @i int
declare @strChar nvarchar(500)
declare @CleanedString nvarchar(500)
--initiate values
set @CleanedString =''
set @theString = @theString + ''
SET @i = 1
--Determine if we are looking for numeric values only or numbers and letters
SET @strAlphaNumeric = case @CleanMode
WHEN 1
THEN '0123456789'
WHEN 2
THEN '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
WHEN 3
THEN '|0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
else 0
end
--Search through chars in the string passed to the function
while (@i <= Len(@theString))
begin
set @strChar = substring(@theString, @i, 1);
If (charindex(@strAlphaNumeric, @strChar) <>0) --if the current char being reviewed is valid then add it to the new string
begin
SET @CleanedString = @CleanedString + @strChar;
end
END
return @CleanedString;
END