\usepackage{color}
\usepackage{listings}
\lstset{language=C,
                \lstset{literate=% damit Umlaute in Kommentaren richtig dargestellt werden
                       {Ö}{{\"O}}1
                       {Ä}{{\"A}}1
                       {Ü}{{\"U}}1
                       {ß}{{\ss}}1
                       {ü}{{\"u}}1
                       {ä}{{\"a}}1
                       {ö}{{\"o}}1
                       {~}{{\textasciitilde}}1
                }
                basicstyle=\ttfamily,
                keywordstyle=\color{blue}\ttfamily,
                stringstyle=\color{red}\ttfamily,
                commentstyle=\color{green}\ttfamily,
                morecomment=[l][\color{magenta}]{\#}
            }

\begin{lstlisting}
for (int i=1; i<100; i++){
  ...
}
\end{lstlisting}

Man kann auch ganze Files einbinden:

\lstinputlisting{main.c}