Cross-referencing in LaTeX

\documentclass{article}
\begin{document}

\section{Introduction}
\label{sec:intro}
This is the introduction section.

\section{Methods}
\label{sec:methods}
As mentioned in Section~\ref{sec:intro}, we will now discuss methods.

\subsection{Data Collection}
\label{subsec:data}
Data collection procedures are described here.

\section{Results}
According to the methods in Section~\ref{sec:methods} and specifically 
the data collection in Section~\ref{subsec:data}, our results show...

\end{document}

% Step 1: Add labels to elements you want to reference
\section{Literature Review}
\label{sec:literature}

\begin{figure}[htbp]
  \centering
  \includegraphics[width=0.8\textwidth]{diagram.png}
  \caption{System architecture}
  \label{fig:architecture}
\end{figure}

\begin{equation}
E = mc^2
\label{eq:einstein}
\end{equation}

% Step 2: Reference them in text
As shown in Figure~\ref{fig:architecture}, the system...
Einstein's equation (Equation~\ref{eq:einstein}) demonstrates...
The literature review in Section~\ref{sec:literature} covers...

% Sections and chapters
\chapter{Introduction}
\label{chap:intro}

\section{Background}
\label{sec:background}

\subsection{Previous Work}
\label{subsec:previous}

% Figures and tables
\begin{figure}
  \caption{Results overview}
  \label{fig:results}
\end{figure}

\begin{table}
  \caption{Performance comparison}
  \label{tab:performance}
\end{table}

% Equations
\begin{equation}
  y = mx + b
  \label{eq:linear}
\end{equation}

% Algorithms and listings
\begin{algorithm}
  \caption{Sorting algorithm}
  \label{alg:sort}
\end{algorithm}

% Appendices
\appendix
\section{Additional Data}
\label{app:data}

% Examples and theorems
\begin{theorem}
  \label{thm:main}
  Statement of theorem...
\end{theorem}

\begin{example}
  \label{ex:basic}
  Example content...
\end{example}

% Basic page reference
See the discussion on page~\pageref{sec:methods}.

% Combined references
Figure~\ref{fig:results} on page~\pageref{fig:results} shows...

% Reference with both number and page
Equation~\ref{eq:main} (page~\pageref{eq:main}) demonstrates...

% Checking if reference is on current page
\ifthenelse{\equal{\pageref{fig:test}}{\thepage}}{%
  Figure~\ref{fig:test} above shows...
}{%
  Figure~\ref{fig:test} on page~\pageref{fig:test} shows...
}

\usepackage{amsmath}

% Numbered equation with reference
\begin{equation}
  \label{eq:quadratic}
  x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
\end{equation}

% Reference equation in text
The quadratic formula (Equation~\ref{eq:quadratic}) provides...

% Using \eqref for automatic parentheses
The solution is given by~\eqref{eq:quadratic}.

% Multiple equations with sub-references
\begin{subequations}
\label{eq:system}
\begin{align}
  x + y &= 5 \label{eq:system-a} \\
  2x - y &= 1 \label{eq:system-b}
\end{align}
\end{subequations}

% Referencing the system and individual equations
The system~\eqref{eq:system} consists of equations~\eqref{eq:system-a} 
and~\eqref{eq:system-b}.

\usepackage{subcaption}

\begin{figure}[htbp]
  \centering
  \begin{subfigure}[b]{0.45\textwidth}
    \includegraphics[width=\textwidth]{image1.png}
    \caption{First result}
    \label{fig:results-a}
  \end{subfigure}
  \hfill
  \begin{subfigure}[b]{0.45\textwidth}
    \includegraphics[width=\textwidth]{image2.png}
    \caption{Second result}
    \label{fig:results-b}
  \end{subfigure}
  \caption{Experimental results}
  \label{fig:results}
\end{figure}

% Referencing main figure and subfigures
Figure~\ref{fig:results} shows our experimental results. 
Specifically, Figure~\ref{fig:results-a} demonstrates the first outcome,
while Figure~\ref{fig:results-b} shows the second.

\usepackage{cleveref}

% cleveref automatically determines reference type
\cref{sec:intro}        % → section 1
\cref{fig:results}      % → figure 2
\cref{tab:data}         % → table 3
\cref{eq:main}          % → equation (4)

% Capitalized versions
\Cref{sec:intro}        % → Section 1
\Cref{fig:results}      % → Figure 2

% Multiple references
\cref{fig:a,fig:b,fig:c}     % → figures 1, 2 and 3
\cref{eq:1,eq:2,eq:3}        % → equations (1) to (3)
\cref{sec:intro,sec:methods} % → sections 1 and 2

% Range references
\crefrange{fig:first}{fig:last}  % → figures 1 to 5
\Crefrange{eq:start}{eq:end}     % → Equations (1) to (3)

\usepackage{cleveref}

% Customize reference formats
\crefname{figure}{fig.}{figs.}           % figure → fig.
\Crefname{figure}{Fig.}{Figs.}          % Figure → Fig.

\crefname{table}{tab.}{tabs.}           % table → tab.
\Crefname{table}{Tab.}{Tabs.}           % Table → Tab.

\crefname{equation}{eq.}{eqs.}          % equation → eq.
\Crefname{equation}{Eq.}{Eqs.}          % Equation → Eq.

\crefname{section}{sect.}{sects.}       % section → sect.
\Crefname{section}{Sect.}{Sects.}       % Section → Sect.

% Custom theorem-like environments
\newtheorem{theorem}{Theorem}
\crefname{theorem}{theorem}{theorems}
\Crefname{theorem}{Theorem}{Theorems}

% Usage examples
\cref{fig:test}     % → fig. 1
\Cref{fig:test}     % → Fig. 1
\cref{thm:main}     % → theorem 1
\Cref{thm:main}     % → Theorem 1

% Conjunctions and lists
\cref{fig:a,fig:b}              % → figures 1 and 2
\cref{fig:a,fig:b,fig:c}        % → figures 1, 2 and 3
\cref{fig:a,fig:b,fig:c,fig:d}  % → figures 1 to 4

% Custom conjunctions
\crefname{figure}{figure}{figures}
\newcommand{\crefrangeconjunction}{--}  % Change "to" to "--"
\crefrange{fig:first}{fig:last}         % → figures 1--5

% Sorting and compression
\cref{fig:c,fig:a,fig:b}        % → figures 1, 2 and 3 (auto-sorted)
\cref{eq:1,eq:2,eq:3,eq:4,eq:5} % → equations (1) to (5) (compressed)

% Cross-reference without number
\namecref{fig:test}             % → figure (without number)
\nameCref{fig:test}             % → Figure (without number)

% Reference format for specific instances
\labelcref{fig:test}            % → 1 (just the number)
\labelcpageref{fig:test}        % → 5 (just the page number)

\usepackage{hyperref}
\usepackage{cleveref} % Load AFTER hyperref

% Configure hyperref
\hypersetup{
  colorlinks=true,
  linkcolor=blue,        % Internal links
  citecolor=green,       % Citations
  filecolor=magenta,     % File links
  urlcolor=cyan,         % URL links
  bookmarks=true,        % PDF bookmarks
  pdfborder={0 0 0}     % Remove boxes around links
}

% All references are now clickable
\section{Introduction}
\label{sec:intro}

\section{Methods}
As discussed in \cref{sec:intro}...  % Clickable blue link

% Customize link appearance
\hypersetup{
  linkcolor=black,       % Black links
  colorlinks=false,      % Boxes instead of colors
  pdfborder={0 0 1}     % Thin border
}

\usepackage{hyperref}

\hypersetup{
  pdftitle={Document Title},
  pdfauthor={Author Name},
  pdfsubject={Subject},
  pdfkeywords={keyword1, keyword2, keyword3},
  bookmarks=true,
  bookmarksopen=true,
  bookmarksdepth=3,      % Depth of bookmark tree
  pdfstartview=FitH      % Initial view
}

% Bookmarks are automatically generated from sections
\section{Introduction}        % Appears in PDF bookmarks
\subsection{Background}       % Nested bookmark
\subsubsection{Related Work}  % Deeper nesting

% Custom bookmark entries
\pdfbookmark[0]{Custom Entry}{custom}  % Level 0 bookmark
\pdfbookmark[1]{Sub Entry}{sub}        % Level 1 bookmark

\usepackage{amsthm}
\usepackage{cleveref}

% Define theorem environments
\newtheorem{theorem}{Theorem}[section]
\newtheorem{lemma}[theorem]{Lemma}
\newtheorem{corollary}[theorem]{Corollary}
\newtheorem{proposition}[theorem]{Proposition}

\theoremstyle{definition}
\newtheorem{definition}[theorem]{Definition}
\newtheorem{example}[theorem]{Example}

\theoremstyle{remark}
\newtheorem{remark}[theorem]{Remark}

% Configure cleveref names
\crefname{theorem}{theorem}{theorems}
\Crefname{theorem}{Theorem}{Theorems}
\crefname{lemma}{lemma}{lemmas}
\Crefname{lemma}{Lemma}{Lemmas}
\crefname{definition}{definition}{definitions}
\Crefname{definition}{Definition}{Definitions}

% Usage
\begin{theorem}
\label{thm:main}
This is the main theorem.
\end{theorem}

\begin{proof}
The proof follows from \cref{thm:main}...
\end{proof}

\begin{lemma}
\label{lem:helper}
This lemma supports the main theorem.
\end{lemma}

% References in text
\Cref{thm:main} establishes... % → Theorem 1 establishes...
\cref{lem:helper} provides...  % → lemma 2 provides...

\usepackage{algorithm}
\usepackage{algpseudocode}
\usepackage{cleveref}

% Configure algorithm references
\crefname{algorithm}{algorithm}{algorithms}
\Crefname{algorithm}{Algorithm}{Algorithms}

\begin{algorithm}
\caption{Quicksort algorithm}
\label{alg:quicksort}
\begin{algorithmic}[1]
\Procedure{QuickSort}{$A, p, r$}
\If{$p < r$}
    \State $q \gets \Call{Partition}{A, p, r}$
    \State \Call{QuickSort}{$A, p, q-1$}
    \State \Call{QuickSort}{$A, q+1, r$}
\EndIf
\EndProcedure
\end{algorithmic}
\end{algorithm}

% Reference in text
\Cref{alg:quicksort} shows the implementation...
The complexity of \cref{alg:quicksort} is...

% In main document
\usepackage{xr}
\externaldocument{chapter1}  % References chapter1.tex
\externaldocument{chapter2}  % References chapter2.tex

% Can now reference labels from external documents
As shown in \cref{fig:external-result} (from Chapter 1)...
\Cref{tab:comparison} in Chapter 2 demonstrates...

% Avoiding label conflicts
\externaldocument[ch1-]{chapter1}  % Prefix all labels with "ch1-"
\externaldocument[ch2-]{chapter2}  % Prefix all labels with "ch2-"

% References now need prefixes
\cref{ch1-fig:result}
\cref{ch2-tab:data}

% Main document structure
% main.tex
\documentclass{book}
\usepackage{hyperref}
\usepackage{cleveref}

% Include chapters
\include{chapters/introduction}    % \input doesn't work with xr
\include{chapters/literature}
\include{chapters/methodology}
\include{chapters/results}
\include{chapters/conclusion}

% Each chapter file can reference others
% chapters/results.tex
\chapter{Results}
\label{chap:results}

As discussed in \cref{chap:introduction}, our methodology 
(\cref{chap:methodology}) leads to the following results...

\section{Experimental Setup}
\label{sec:setup}
The setup described here builds on \cref{sec:literature-review}...

\usepackage{ifthen}

% Check if reference exists
\newcommand{\safecref}[1]{%
  \ifthenelse{\equal{\ref{#1}}{??}}{%
    [Reference not found]%
  }{%
    \cref{#1}%
  }%
}

% Check if on same page
\newcommand{\smartref}[1]{%
  \ifthenelse{\equal{\pageref{#1}}{\thepage}}{%
    \cref{#1} above%
  }{%
    \cref{#1} on page~\pageref{#1}%
  }%
}

% Usage
\smartref{fig:test}  % → "figure 1 above" or "figure 1 on page 5"

% Define convenient macros
\newcommand{\figref}[1]{Figure~\ref{#1}}
\newcommand{\tabref}[1]{Table~\ref{#1}}
\newcommand{\eqnref}[1]{Equation~\eqref{#1}}
\newcommand{\secref}[1]{Section~\ref{#1}}
\newcommand{\chapref}[1]{Chapter~\ref{#1}}

% Enhanced macros with page references
\newcommand{\figpref}[1]{Figure~\ref{#1} on page~\pageref{#1}}
\newcommand{\tabpref}[1]{Table~\ref{#1} on page~\pageref{#1}}

% Usage
\figref{fig:results} shows...      % → Figure 1 shows...
\tabpref{tab:data} contains...     % → Table 1 on page 3 contains...