Weird vertical lines with table

Question

Using the code:

\documentclass[a4paper]{article}   
\usepackage{ngerman} 
\begin{document}
\begin{table}[htb]
\begin{center}
\begin{tabular}{|c|c|c|}
\hline
\textbf{Value A}&\textbf{Value B}&\textbf{Value C} \\
\hline 
\hline
\\ \( 1) & \( 17) & \( 98) \\ \\
\hline
\\ \( x = \frac{42}{5} \cdot x + n\) & \( y = \frac{17}{2} \cdot y + n\) & \( 0\) \\ \\
\hline
\hline
\end{tabular}
\end{center}
\caption{Stuff}
\end{table}
\end{document}

I get

Answer 1

Don't do

\hline \\ 

as that generates a truncated line with only the cell in the first column, hence the missing line segments, just do

\\

If you want to space out the array, use \arraystretch.

Answer 2

Good style advice for tables is available in the documentation for the booktabs package. Here it is strongly recommended not to use vertical rules, nor double horizontal rules. Furthermore to provide bigger row spacing in the table you should adjust \arraystretch (which is a command containing a factor) rather than adding blank rows.

\documentclass[a4paper]{article}   

\usepackage{ngerman} 
\usepackage{booktabs}

\begin{document}

\begin{table}[htb]
  \begin{center}
    \renewcommand*{\arraystretch}{1.5}
    \begin{tabular}{ccc}
      \toprule
      Bereich (I) in Nm&Bereich (II) in Nm&Bereich (III) in Nm \\ 
      \midrule
      \( M_{t1} = 0\) & \( M_{t2} = 150\) & \( M_{t3} = 150\) \\ 
      \( M_{by1}(x) = \frac{450}{43} \cdot x + n\)
        & \( M_{by2}(x) = -\frac{450}{43} \cdot x + n\)
        & \( M_{by3}(x) = 0\) \\ 
      \( M_{bz1}(x) = \frac{65}{43} \cdot x + n\)
        & \( M_{bz2}(x) = -\frac{65}{43} \cdot x + n\)
        & \( M_{bz3}(x) = 0\) \\
      \bottomrule
    \end{tabular}
  \end{center}
  \caption{Momente \textit{abgelesen}}
\end{table}

\end{document}