SSIS Execute sql task and variables

I am newbie to SSIS. I want to run an Execute sql task in control flow. Control flow does not provide any derived column task or so.. I want to prepare a sql statement and put it in a variable and then I can use that in execute sql task.

I have defined a variable called sqlstatment. When I went to set its value; I set it as:

‘truncate table ‘ +   User::vschema + ‘.’ + employee

Now when I run execute sql task, it is complaining about syntax of sqlstatement. Cannot figure out the error:

A few questions:

1. Can I define value of a variable sqlstatment which is an expression.
2. How do I debug what is the value of variable when I am executing control flow.

Appreciate any help.