Adding emptyset in my pseudocode

Question

I am trying to write some pseudocode using verbatim. The problem is, I can't get it write the right symbols. Here's my code:

\begin{verbatim}
    S= $\emptyset$
    while ((not ottimo(S) ) and (C \ne $\emptyset$))
         x = seleziona(C)
         C = C – {x}
         if (ammissibile(S U {x}))
               S = S U {x}
    if (ottimo(S))
         return S
    else
         return $\emptyset$

\end{verbatim}

If I write $\emptyset$ shows it exactly as it is written, but if I use Ø it returns error.

How can I fix it?

ps. it does the same with every other symbol, like not equal, ...

Answer 1

I don't think this is the best way to present pseudocode. Anyway, you can use alltt, but symbols will look very different.

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{alltt}

\begin{document}

\begin{alltt}
    S = \(\emptyset\)
    while ((not ottimo(S) ) and (C \(\ne\) \(\emptyset\)))
         x = seleziona(C)
         C = C – \{x\}
         if (ammissibile(S U \{x\}))
               S = S U \{x\}
    if (ottimo(S))
         return S
    else
         return \(\emptyset\)

\end{alltt}

\end{document}

You may want to use the algpseudocode package, which provides customizable features for the purpose.

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{algpseudocode}
\usepackage{amsmath}

\newcommand{\fun}[1]{\mathrm{#1}}% functions
\newcommand{\NOT}{\operatorname{not}}
\newcommand{\AND}{\mathbin{\mathrm{and}}}

\begin{document}

\begin{algorithmic}[1]
\State $S = \emptyset$
\While{$(\NOT \fun{ottimo}(S) ) \AND (C \ne\emptyset)$}
  \State $x = \fun{seleziona}(C)$
  \State $C = C - \{x\}$
  \If{$(\fun{ammissibile}(S\cup \{x\}))$}
    \State $S = S \cup \{x\}$
    \If{$(\fun{ottimo}(S))$}
      \State return $S$
    \Else
      \State return $\emptyset$
    \EndIf
  \EndIf
\EndWhile
\end{algorithmic}

\end{document}

Answer 2

If you load fontspec, use only Unicode symbols and no LaTeX commands, and select a monospaced font that contains all those symbols, you can use verbatim.

\tracinglostchars=2 % Warn if a glyph is missing from the font!
\documentclass{article}
\usepackage{fontspec}

\setmonofont{DejaVu Sans Mono}

\pagestyle{empty} % Suppress page numbering for MWE.

\begin{document}
\begin{verbatim}
    S = Ø
    while ((not ottimo(S)) and (C ≠ Ø))
         x = seleziona(C)
         C = C – {x}
         if (ammissibile(S ∪ {x}))
               S = S ∪ {x}
    if (ottimo(S))
         return S
    else
         return Ø
\end{verbatim}
\end{document}

You cannot enter math mode or use commands within verbatim. There are several packages that format pseudocode more attractively than this, but that’s one way to get the retro look.