code for splitting cell into two

Question

Please can anyone tell me what code should I write for this type of cell splitting?

Answer 1

Is this meets your requirement?

\documentclass{book}
\begin{document}
\begin{tabular}{|l|l|p{4pc}|p{4pc}|}%%change the value 4pc, whatever you likes
\hline
Serial Number &Loops/Iteration &\multicolumn{2}{|l|}{Execution Time}\
\cline{3-4}
& &Execution Time Per Loop &Total Execution Time\
\hline
\end{tabular}
\end{document}

Answer 2

If you are new to LaTeX, you might need to read a tutorial to get familiar with its language. Here's a particular info on tables but usually more a custom tables require more code than just an environment and the content.

In almost all cases, it's better to merge cells rather than split. If you need to tabulate texts, it's also more convenient to use p{}-type column than regular l, c, or r. p{} converts cells into paragraphs and adds line breaks if necessary or let you add line breaks manually.

The table

and code

\documentclass{article}
\usepackage{array}
\usepackage{multirow}
\newcolumntype{P}[1]{>{\raggedright\arraybackslash}p{#1}}
\begin{document}
\begin{table}[tbh]
  \centering
  \renewcommand*{\arraystretch}{1.25}
  \caption{Cation}\label{tab:table}
  \vspace{3pt}%
  \begin{tabular}{|P{1.5cm}|P{2.5cm}|P{3cm}|P{3cm}|}
    \hline
    \multirow[t]{2}={Special number}
    & \multirow[t]{2}={Loops/Iteration}
    & \multicolumn{2}{l|}{Execution time} \
    \cline{3-4}
    & & Execution\newline Time per Loop & Total execution Time \
    \hline
  \end{tabular}
\end{table}
\end{document}