如何在代码块上放置下标

Question

您好，如何在代码块中放置下标？

\documentclass{article}
\usepackage{xcolor}
\usepackage{listings}
\usepackage{float}
\usepackage{amsmath}  
\usepackage[a4paper,margin=1in,footskip=0.25in]{geometry}
\usepackage{graphicx}
\graphicspath{ {./images/} }
\colorlet{mygray}{black!30}
\colorlet{mygreen}{green!60!blue}
\colorlet{mymauve}{red!60!blue}
\parindent 0px
\lstset{
  backgroundcolor=\color{gray!10},  
  basicstyle=\ttfamily,
  columns=fullflexible,
  breakatwhitespace=false,      
  breaklines=true,                
  captionpos=b,                    
  commentstyle=\color{mygreen}, 
  extendedchars=true,              
  frame=single,                   
  keepspaces=true,             
  keywordstyle=\color{blue},      
  language=c++,                 
  numbers=none,                
  numbersep=5pt,                   
  numberstyle=\tiny\color{blue}, 
  rulecolor=\color{mygray},        
  showspaces=false,               
  showstringspaces=false,
  showtabs=false,                 
  stepnumber=5,                  
  stringstyle=\color{mymauve},   
  tabsize=3,                      
  title=\lstname                
}
\begin{document}


\begin{lstlisting}
Test_k
\end{lstlisting}

\end{document} 

Answer 1

mathescape最简单的方法可能是使用命令中的选项\lstset。

\lstset{
  mathescape,
  backgroundcolor=\color{gray!10},  
  basicstyle=\ttfamily,
  columns=fullflexible,
  breakatwhitespace=false,      
  breaklines=true,                
  captionpos=b,                    
  commentstyle=\color{mygreen}, 
  extendedchars=true,              
  frame=single,                   
  keepspaces=true,             
  keywordstyle=\color{blue},      
  language=c++,                 
  numbers=none,                
  numbersep=5pt,                   
  numberstyle=\tiny\color{blue}, 
  rulecolor=\color{mygray},        
  showspaces=false,               
  showstringspaces=false,
  showtabs=false,                 
  stepnumber=5,                  
  stringstyle=\color{mymauve},   
  tabsize=3,                      
  title=\lstname                
}


\begin{document}


\begin{lstlisting}
Test$_k$
Test$^k$
\end{lstlisting}

\end{document} 

这将为您提供：