Increment counter with name based on input

Question

I have different counters, and I want to increment them. After I do not want to increment them separately, I wanted to write a macro which does that for me, depending on the input. I have the following code:

\documentclass[10pt,a4paper]{book}
\usepackage[latin1]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{tikz}
\usepackage{tocloft}

\newcounter{countera}
\newcounter{counterb}
\newcommand{\toC}[1]{
    \stepcounter{%
        \expandafter\csname counter#1\endcsname%
        }
}
\begin{document}
\toC{a}
\end{document}

When I now want to increment counter countera, I just want to call \toC{a} instead of \stepcounter{countera}. By using the code above, I get a lot of errors, such as ! Missing \endcsname inserted., ! Extra \endcsname. and ! LaTeX Error: No counter '\countera ' defined. The macro \toC{} will be expanded later, thus I would prefer to keep its structure like this, if possible. Why do I get those errors?

Answer 1

Do you mean this?

\documentclass[10pt,a4paper]{book}
\usepackage[latin1]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{tikz}
\usepackage{tocloft}

\newcounter{countera}
\newcounter{counterb}
\newcommand{\toC}[1]{%
  \stepcounter{%
    counter#1%
  }
}
\begin{document}
\toC{a}
\toC{b}

\thecountera

\thecounterb

\end{document}