# Undefined control sequence in VTEX

I am using VTEX (visual Tex). When I run this program, it shows a error message that is

! Undefined control sequence.
\convertto #1#2->\strip@pt \dimexpr
#2*65536/\number \dimexpr 1#1
?


But this program runs in LaTeX successfully. How can I solve this error?

\documentclass{article}

\makeatletter
\def\convertto#1#2{\strip@pt\dimexpr #2*65536/\number\dimexpr 1#1}
\makeatother

\begin{document}
\newdimen\mylength
\mylength=1in
\convertto{cm}{\the\mylength}cm
\end{document}


Output: 2.54 cm

The error occurs as VTeX does not have the e-TeX extensions enabled. These extensions to Kunth's TeX (TeX90) provide for example \dimexpr as a primitive. The extensions were finalised in 1999 and are available in all major (free) TeX systems available today. However, according to http://www.micropress-inc.com/new.htm the last update to VTeX was around 10 years ago and does not feature these. Thus you cannot use any code which needs the extensions: they are increasingly commonly used.