how to combine two variables in cmd.exe script

In a cmd.exe script on Windows 7, I want to combine two variables to set a 开发者_StackOverflow社区third.

Eg. (which doesn't work)

SET THIRD=%FIRST%%SECOND%

How can I do this ?

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Apologies to everyone who even looked at this question. The example above works perfectly and I cannot reproduce the problem I was having. Thanks for pointing out my error.

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With quotes?

SET "THIRD=%FIRST%%SECOND%"