[tex-eplain] Strike out in TeX

[Guy Worthington]

> if you want to strike out each letter individually

The algorithm comes from a pretty-printing macro package called
c_pascal.  A quick search of CTAN has it at macros/generic/c_pascal.

%-test.tex-----------------------------------------------------------
\newcount\CharCode
\newif\ifDigit
\newif\ifPunctuation

\def\isDigit#1{%
  \Digitfalse
  \ifnum `\/ < #1\relax
    \ifnum `\: > #1\relax \Digittrue \fi \fi
  \ifDigit}

\def\isPunctuation#1{%
  \fi% matches \ifDigit...\else...\fi
  \Punctuationfalse
  \ifnum `\, = #1\relax \Punctuationtrue \fi
  \ifnum `\. = #1\relax \Punctuationtrue \fi
  \ifPunctuation}
      
\def\Strike#1{%
   \expandafter\ReadChar#1}
  
% the argument is a single number
\def\ReadChar#1{%
  \let\WhatNext = \ReadChar%
  \global\CharCode = `#1\relax%
  \isDigit{\CharCode}/\llap#1%
    \else \isPunctuation{\CharCode}#1%
       \else #1\relax \let\WhatNext = \relax \fi%
  \WhatNext}

Here is a number in text mode: \Strike{123,456,789.01}\ (don't forget
the space after the macro).

Here is a number in math mode: $\Strike{123456}$.

\bye
%------------------------------------------------------------