Trouble setting a length [closed]

Question

I'm starting with LaTeX, and there are things that puzzle me. I'm trying to set a length that's the \textwidth minus (let's say for example) two inches. In the preamble, I wrote:

\newlength{\bplen}
\setlength{\bplen}{\textwidth}
\addtolength{\pblen}{-2in}

The compiler tells me:

! Undefined control sequence. <argument> \pblen 
l.21 \addtolength{\pblen}{-2in}
! You can't use `blank space  ' after \advance.
\addtolength #1#2-<\advance #1 
                               #2\relax
l.21 \addtolength{\pblen}{-2in}
! LaTeX Error: Missing \begin{document}.

I've just defined \bplen and what's that about a missing \begin{document}? Aren't I allowed to set lengths in the preamble?

Answer 1

Could it be simply a typo? Your first and your second code line contain \bplen, but your third \pblen.

EDIT: Without the typo your code works as intended:

\documentclass{article}

\newlength{\bplen}
\setlength{\bplen}{\textwidth}
\addtolength{\bplen}{-2in}

\begin{document}

Value of textwidth: \the\textwidth

Value of bplen: \the\bplen

\end{document}