Question : TSQL decimal

What's wrong with following sql

Declare @Decimals Integer
Declare @Digits Decimal
DECLARE @myval varchar(9)

Set @Decimals  = 3
Set @Digits = (9 - @Decimals)
SET @myval = 193.57

select convert(decimal(@Digits,@Decimals),@myval)

Following line works but why i cannot pass a variable?
select convert(decimal(9,3),@myval)

Answer : TSQL decimal

If myVal is currently VARCHAR and has a decimal point in it, you can do this to get a truncated value:

SELECT LEFT(myValue, CHARINDEX('.', myValue) + [decimal])
FROM myTable