\documentclass[12pt]{article}

\usepackage{verbatim,moreverb}
\def\listingoffset{1em}
\def\listinglabel#1{\llap{\tiny\it\the#1}\hskip\listingoffset\relax}
\def\mylisting#1{{\fontsize{10}{11}\selectfont\listinginput[1]{1}{#1}}}
\def\myoutput#1{{\fontsize{10}{11}\selectfont\verbatimtabinput{#1}}}

\begin{document}

I wrote a program called flops.c that solves a system
of linear equations $Ax=b$.
Note, the solution obtained by Gaussian elimination satisfies
$$
	b_i=\sum_{j=1}^n A_{ij} x_j.
$$
The program was this:

\mylisting{flops.c}

The output was this:

\myoutput{flops.out}

\end{document}