Convert string to integer?

[richiebabes]

I am trying to read a text file to get a version number from it. I then want to compare that to the current version and abort if a newer version is already installed. This is what I have so far:

; check existing version
Push 1
Push "$INSTDIR\config\version.txt"
Call ReadFileLine
Pop $0

${If} $0 > 730
MessageBox MB_OK "A newer version of blah is already installed on this machine. Please uninstall it first."
Abort
${EndIf}

The problem is that $0 is a string and I can't find anywhere in the documentation how to convert it to an integer. I don't want to compare strings because 730 would be bigger than 1000.

How do I convert $0 to an integer?