Error with subfigure and TikZ

Question

I'm trying to include two TikZ pictures in one figure:

\documentclass[12pt]{scrbook}
\usepackage{tikz}
\usepackage{amsmath,amssymb}
\usepackage{subfigure}

\begin{document}

\begin{figure}[h]
    \begin{subfigure}[b]{0.49\textwidth}
        \centering
        \resizebox{\linewidth}{!}{TikZ/QuadrateResiduenParabola}
     \caption{Text.}
    \end{subfigure}

    \begin{subfigure}[b]{0.49\textwidth}
        \centering
        \resizebox{\linewidth}{!}{TikZ/QuadrateResiduenParaboloid}
     \caption{More text.}
    \end{subfigure}
\end{figure}

\end{document}

Here I get the following error message:

Missing number, treated as zero. \begin{subfigure}[b]{0.49\textwidth}
Illegal unit of measure (pt inserted). \begin{subfigure}[b]{0.49\textwidth}

What is wrong?

Answer 1

There are a few problems with your code:

First, \resizebox just resizes what it is given, it doesn't look for files anywhere. Hence, if you do

\documentclass{article}
\usepackage{graphicx}
\begin{document}
TikZ/QuadrateResiduenParaboloid

\resizebox{\linewidth}{!}{TikZ/QuadrateResiduenParaboloid}
\end{document}

you get

To actually insert the contents of the .tex file, you need \input as well:

\resizebox{\linewidth}{!}{\input{TikZ/QuadrateResiduenParaboloid}}

The second is that you've loaded the wrong package for subfloats. The subfigure package that you've loaded does not define a subfigure environment, it defines a \subfigure macro, that is used as \subfigure[<list entry>][<subcaption>]{<figure>}. But that package is considered deprecated, so you shouldn't use it.

The syntax you have used is actually defined by the subcaption package, so you should replace \usepackage{subfigure} with \usepackage{subcaption}.

And finally, an empty line signifies a paragraph break, also inside a figure environment, so you need to remove the one between the subfigure environments, otherwise they will end up one above the other.

Complete code:

\documentclass[12pt]{scrbook}
\usepackage{tikz}
\usepackage{amsmath,amssymb}
\usepackage{subcaption}

\begin{document}

\begin{figure}[h]
    \begin{subfigure}[b]{0.49\textwidth}
        \centering
        \resizebox{\linewidth}{!}{\input{TikZ/QuadrateResiduenParabola}}
     \caption{Text.}
    \end{subfigure}\hfill
    \begin{subfigure}[b]{0.49\textwidth}
        \centering
        \resizebox{\linewidth}{!}{\input{TikZ/QuadrateResiduenParaboloid}}
     \caption{More text.}
    \end{subfigure}
\end{figure}

\end{document}