Conflict between main.tex and input child.tex

Question

When I run child.tex, then table created with right formatting.

When I run main.tex, with \input{child.tex}, then table in child.tex created with wrong formatting.

child.tex code from: Error: Not in outer par mode: table inside tcolorbox

\documentclass[12pt,a4paper,
               x11names,table]{article}
\usepackage{tcolorbox}
\usepackage[skip=1ex]{caption}

\begin{document}

\begin{tcolorbox}[colback=gray!5!white,colframe=gray!75!black,title=\large{In the next lines I'm trying to insert the same in a box}]
\centering
\begin{tabular}{|c|c|c|c|}
  \hline
  % after \\: \hline or \cline{col1-col2} \cline{col3-col4} ...
  a& b & T/F & dif\\ \hline
1 & 2 & False & -1\\
2 & 4 & False & -2\\
  \hline
\end{tabular}\\
\captionof{figure}{Caption Table}\label{tab:table-out}
    \end{tcolorbox}
\end{document}

And in main.tex:

\documentclass[12pt,a4paper]{article}
a lot of usepackage
\begin{document}
\input{child.tex}
\end{document}

How can I clear format of main.tex inside child.tex?

Answer 1

You can not have two \documentclass, \begin{document} and \end{document} commands in one TeX code!

Please see the following MWE (package filecontents is only used to have both TeX codes in one compiling MWE, you do not need to use filecontents in your code!) and please see the comments in code for main.tex:

\RequirePackage{filecontents}
\begin{filecontents}{child.tex}
\begin{tcolorbox}[colback=gray!5!white,colframe=gray!75!black,title=\large{In the next lines I'm trying to insert the same in a box}]
\centering
\begin{tabular}{|c|c|c|c|}
  \hline
  % after \\: \hline or \cline{col1-col2} \cline{col3-col4} ...
  a& b & T/F & dif\\ \hline
1 & 2 & False & -1\\
2 & 4 & False & -2\\
  \hline
\end{tabular}\\
\captionof{figure}{Caption Table}\label{tab:table-out}
\end{tcolorbox}
\end{filecontents}


% your code main.tex following % <===========================================
\documentclass[%
  12pt,a4paper,
  x11names,table
]{article}

\usepackage{tcolorbox} % all needed packages for child.tex have to be called here!
\usepackage[skip=1ex]{caption}

\begin{document}
\input{child.tex} % only code for environment tcolorbox
\end{document}

giving you the resulting pdf:

You get the same output with following both files.

First child.tex:

\begin{tcolorbox}[colback=gray!5!white,colframe=gray!75!black,title=\large{In the next lines I'm trying to insert the same in a box}]
\centering
\begin{tabular}{|c|c|c|c|}
  \hline
  % after \\: \hline or \cline{col1-col2} \cline{col3-col4} ...
  a& b & T/F & dif\\ \hline
1 & 2 & False & -1\\
2 & 4 & False & -2\\
  \hline
\end{tabular}\\
\captionof{figure}{Caption Table}\label{tab:table-out}
\end{tcolorbox}

and second main.tex:

\documentclass[%
  12pt,a4paper,
  x11names,table
]{article}

\usepackage{tcolorbox}
\usepackage[skip=1ex]{caption}

\begin{document}
\input{child.tex}
\end{document}

Please do us and yourself a favour and read the documentation of package filecontents for example by typing texdoc filecontents in your terminal/console and press then enter ... This package is very helpful for building MWE for testing purposes like in your case ...