The layout is not coming out as expected after using subsections [duplicate]

Question

I have inserted tables and images with the \subsection to make different parts in the report and I wrote it in order but the output is not in order when getting compiled, the subsection does not come after the table I want it to. I have attached the source code below. Any help will be appreciated.

I compared and analysed codes using the MPI library to find out the performance difference between C and Python programs.

\section{Integration}
Finding out the total integration under the curve for a fixed function with limits 0 to 2. 
\[ f(x)=\int\limits_0^1 x^2 \]
I have used the Trapezoidal Rule for calculating the same. It is a Numerical technique to find the definite integral of a function.The function is divided into many sub-intervals and each interval is approximated by a Trapezium. Then the area of trapeziums is calculated to find the integral which is basically the area under the curve. The more is the number of trapeziums used, the better is the approximation. \\
Algorithm for calculating the integration under the curve is as follows

\lstset{style=mystyle}
\begin{lstlisting}[language= C, caption= Code snippet from IntegrationMPI.c]
    h = (b-a)/n;
    
    local_n = n/size;

    local_a = a + my_rank * local_n * h;

    local_b = (local_a + local_n) * h;

    integral = Trap(local_a, local_b, local_n, h);

    if (my_rank == 0){
        total = integral;
        for (source = 1; source < size; source++){
            MPI_Recv(&integral, 1, MPI_FLOAT, source, tag, MPI_COMM_WORLD, &status);
            total += integral;
        }
    }
    else {
        MPI_Send(&integral, 1, MPI_FLOAT, dest, tag, MPI_COMM_WORLD); 
    }
    
\end{lstlisting}

\subsection{For Serial Program in C and Python}





\begin{table}[h!]
\centering
\begin{tabular}{||c|c|c||} 
 \hline
 No. of Trapeziums & Time Taken (s) & Accuracy \\ [0.5ex] 
 \hline\hline
 1000 & 0.001082 & 2.66666867 \\ 
 \hline
 2000 & 0.001272 & 2.66666743 \\
 \hline
 3000 & 0.002326 & 2.66666681 \\
 \hline
 4000 & 0.003009 & 2.66666675 \\
 \hline
 5000 & 0.003527 & 2.66666672 \\
 \hline
 6000 & 0.004466 & 2.66666670 \\
 \hline
 7000 & 0.004189 & 2.66666669 \\
 \hline
 8000 & 0.004368 & 2.66666669 \\
 \hline
 9000 & 0.007463 & 2.66666669 \\
 \hline
 10000 &  0.007001 & 2.66666669 \\ [1ex] 
 \hline
\end{tabular}
\caption{Data for Python Code}
\label{table:1}
\end{table}



\begin{table}[h!]
\centering
\begin{tabular}{||c|c|c||} 
 \hline
 No. of Trapeziums & Time Taken (s) & Accuracy \\ [0.5ex] 
 \hline\hline
 1000 & 0.000012 & 2.66662788 \\ 
 \hline
 2000 & 0.000030 & 2.66671276 \\
 \hline
 3000 & 0.000032 & 2.66658711 \\
 \hline
 4000 & 0.000052 & 2.66660619 \\
 \hline
 5000 & 0.000058 & 2.66650033 \\
 \hline
 6000 & 0.000064 & 2.66644287 \\
 \hline
 7000 & 0.000074 & 2.66667461 \\
 \hline
 8000 & 0.000084 & 2.66645622 \\
 \hline
 9000 & 0.000084 & 2.66647649 \\
 \hline
 10000 &  0.000103 & 2.66674614 \\ [1ex] 
 \hline
\end{tabular}
\caption{Data for C Code}
\label{table:1}
\end{table}

\begin{figure}[h!]
\centering
\includegraphics[width=1\textwidth]{Images/serial.png}
\caption{Comparison between C and Python serial programs}
\end{figure}


.

\subsection{For MPI Program in C and Python}

\begin{table}[h!]
\centering
\begin{tabular}{||c|c|c||} 
 \hline
 No. of Trapeziums & Time Taken (s) & Accuracy \\ [0.5ex] 
 \hline\hline
 1000 & 0.000549 & 2.66017401 \\ 
 \hline
 2000 & 0.000840 & 2.66341850 \\
 \hline
 3000 & 0.001900 & 2.66450082 \\
 \hline
 4000 & 0.001127 & 2.66504213 \\
 \hline
 5000 & 0.002618 & 2.66536696 \\
 \hline
 6000 & 0.002004 & 2.66558354 \\
 \hline
 7000 & 0.002583 & 2.66573824 \\
 \hline
 8000 & 0.002426 & 2.66585428 \\
 \hline
 9000 & 0.003441 & 2.66594453 \\
 \hline
 10000 &  0.002971 & 2.66601674 \\ [1ex] 
 \hline
\end{tabular}
\caption{Data for Python Code}
\label{table:1}
\end{table}

\begin{table}[h!]
\centering
\begin{tabular}{||c|c|c||} 
 \hline
 No. of Trapeziums & Time Taken (s) & Accuracy \\ [0.5ex] 
 \hline\hline
 1000 & 0.000037 & 2.66016173 \\ 
 \hline
 2000 & 0.000048 & 2.66345334 \\
 \hline
 3000 & 0.000072 & 2.66444683 \\
 \hline
 4000 & 0.000076 & 2.66499472 \\
 \hline
 5000 & 0.000087 & 2.66526604 \\
 \hline
 6000 & 0.000070 & 2.66551304 \\
 \hline
 7000 & 0.000099 & 2.66580105 \\
 \hline
 8000 & 0.000108 & 2.66578150 \\
 \hline
 9000 & 0.000111 & 2.66587353 \\
 \hline
 10000 &  0.000142 & 2.66612148 \\ [1ex] 
 \hline
\end{tabular}
\caption{Data for C Code}
\label{table:1}
\end{table}

\begin{figure}[h!]
\centering
\includegraphics[width=1\textwidth]{Images/mpi.png}
\caption{Comparison between C and Python MPI programs}
\end{figure}

Answer 1

Tables and figures are floats : even with the option [h!] LaTeX will sometimes decide to move them.

What you want is not a float : just remove the \begin{table}[h!] (or \begin{figure}[h!]) at he beginning, and the

\caption{...}
\label{...}
\end{table}

at the end. You can move the text of your captions just below your tabulars or images. For instance:

\subsection{For Serial Program in C and Python}

\begin{center}
\begin{tabular}{||c|c|c||} 
 (...)
\end{tabular}

Data for Python Code
\end{center}

Edit: If you want your table in the List of Tables, you can use the caption package:

\usepackage{capt-of} % or \usepackage{caption}

in your preamble, then

(...)
\end{tabular}

\captionof{table}{Data for Python Code} 
\label{your_label}
\end{center}

in your document.

It's even compatible with hyperref (if hyperref is loaded last):

\autoref{your_label}

The same with figures : \captionof{figure}{your_caption}.