
\documentclass{article}
  \usepackage[latin1]{inputenc}
  \usepackage[T1]{fontenc}
  \usepackage{listings}

\begin{document}
\thispagestyle{empty}

\lstset{language=Pascal,literate={:=}{{$\gets$}}1
  {<=}{{$\leq$}}1 {>=}{{$\geq$}}1 {<>}{{$\neq$}}1}

\begin{lstlisting}
program Toto;
  var i : integer;
begin
  if (i<=0) then i := 1;
  if (i>=0) then i := 0;
  if (i<>0) then i := 0;
end.
\end{lstlisting}
\end{document}
