Why does this listings command keep giving me this error?

Question

\documentclass[titlepage]{article}
\author{foobar}
\title{foofoofoo}
\usepackage{syntonly}
\usepackage{verbatim}
\usepackage{lipsum}
\usepackage{listings}
\begin{document}
\maketitle
\newpage
\tableofcontents
\newpage
\lstset{basicstyle=\texttt} %THIS LINE
\section{Source Code}
I will admit that this code is {\it messy}.
\subsection{foo.c}
\lstinputlisting{foo.c}
\end{document}

I don't understand why that line makes pdflatex not compile; when I remove it, everything works fine.

It gives me this:

! Incomplete \ifmmode; all text was ignored after line 

Answer 1

Since \texttt is a command that expects an argument, it won't find strange characters etc. in listings verbatim mode. It's not possible to give verbatim code as an argument to another command. This is why \texttt{...} must fail.

In order to achieve typewriter font, use \ttfamily to switch to this font. Note, this is an enduring switch (until another switch is applied), whereas \texttt{...} lasts only for the {...} - delimited argument.

\documentclass[titlepage]{article}
\author{foobar}
\title{foofoofoo}
\usepackage{syntonly}
\usepackage{verbatim}
\usepackage{lipsum}
\usepackage{listings}
\begin{document}
\maketitle
\newpage
\tableofcontents
\newpage
\lstset{basicstyle=\ttfamily} %THIS LINE
\section{Source Code}
I will admit that this code is {\textit{messy}}.
\subsection{foo.c}
\lstinputlisting{foo.c}
\end{document}

foo.c:

#include <stdio.h>

int main( int argc, char **argv)
{
  printf("Hello World!\n");
  return(0);
}