As I done the line break inside the cell of the table, the vertical lines has disappeared or not showing up

Question

I've written the below code with the quote from this post.

\documentclass[border=0.1cm]{article}
\usepackage{diagbox}
\usepackage{makecell}
\begin{document}
  \begin{table}\centering\setlength\tabcolsep{3.5pt}\renewcommand\arraystretch{1.25}
      \noindent\makebox[\textwidth]{%
        \begin{tabular}{|l|*{3}{c|}}
          \hline
          \diagbox[width=\dimexpr \textwidth/8+2\tabcolsep\relax, height=1cm,width=3cm]{ row  }{column }
         & smth1 & smth2 \\
          \hline
          smth3   & 1 & 2  \\  
          \hline
          smth4& 3 & 4 \\
          \hline
        \end{tabular}
      }
    \end{table}        


\end{document}

Got the below image from the above code.

As I done line break at the cell of smth3, the blank lines have appeared as shown in the below image.

How can I resolve this problem?

\documentclass[border=0.1cm]{article}
\usepackage{diagbox}
\usepackage{makecell}
\begin{document}
  \begin{table}\centering\setlength\tabcolsep{3.5pt}\renewcommand\arraystretch{1.25}
      \noindent\makebox[\textwidth]{%
        \begin{tabular}{|l|*{3}{c|}}
          \hline
          \diagbox[width=\dimexpr \textwidth/8+2\tabcolsep\relax, height=1cm,width=3cm]{ row  }{column }
         & smth1 & smth2 \\
          \hline
          smth3 \\ text at 2nd row of smth3  & 1 & 2  \\ % Added "\\ text at 2nd row of smth3" 
          \hline
          smth4& 3 & 4 \\
          \hline
        \end{tabular}
      }
    \end{table}        


\end{document}

Answer 1

Use multirow given in How to use \multirow

Here is the complete code

\documentclass[border=0.1cm]{article}
\usepackage{diagbox}
\usepackage{makecell}
\usepackage{multirow}
\begin{document}
        \begin{table}\centering \setlength\tabcolsep{3.5pt}\renewcommand\arraystretch{1.25}
          \noindent\makebox[\textwidth]{%
            \begin{tabular}{|l|*{3}{c|}}
              \hline
              \diagbox[width=\dimexpr \textwidth/8+2\tabcolsep\relax, height=1cm,width=3cm]{ row  }{column }
             & smth1 & smth2 \\
              \hline
              smith3 & \multirow{ 2}{*}{1}  & \multirow{ 2}{*}{2}   \\ % Added "\\ text at 2nd row of smth3" 
              text at 2nd row of smth3 &&\\
              \hline
              smth4& 3 & 4 \\
              \hline
            \end{tabular}
          }
        \end{table}        
\end{document}

Answer 2

\documentclass[border=0.1cm]{article}
\usepackage{diagbox}
\usepackage{makecell}
\begin{document}
\begin{table}\centering\setlength\tabcolsep{3.5pt}\renewcommand\arraystretch{1.25}
    \noindent\makebox[\textwidth]{%
        \begin{tabular}{|l|*{3}{c|}}
            \hline
            \diagbox[width=\dimexpr \textwidth/8+2\tabcolsep\relax, height=1cm,width=4.2cm]{ row  }{column }
            & smth1 & smth2 \\
            \hline
            \makecell[l]{smth3 \\ text at 2nd row of smth3}  & 1 & 2  \\ % Added "\\ text at 2nd row of smth3" 
            \hline
            smth4& 3 & 4 \\
            \hline
        \end{tabular}
    }
\end{table}        


\end{document}