latex Loops - repeating things


Example

We can create loops in latex. They are similar but not as customizable as loops in other programming languages. One alternative to use loops are @loops. If we use a command which includes "@" in its name, we must be put it between \makeatletter and \makeatother. It is not allowed to use them in a macro which describes a new definition.

Wrong:

\def\is#1#2{\makeatletter\@ifstar{#1}{#2}\makeatother

Right:

\makeatletter\def\is#1#2{\@ifstar{#1}{#2}}\makeatother

@for loop: \@for\command:={list}\do{commands}

Example:

\makeatletter
\@for\sun:={rising,setting}\do{The sun is \sun.}
\makeatother

It creates the following text: The sun is rising. The sun is setting.

@whilenum loop: \@whilenum condition\do{commands}

Example:

\makeatletter
\newcounter{int}
\@whilenum\value{int}<10\do
{\stepcounter{int}\ifthenelse{\isodd{\value{int}}}{\theint}{}}
\makeatother

This code writes odd numbers from 1 to 9.

"loop repeat" loop: \loop {commands} \ifnum condition \repeat

Executes commands till condition is true.

Example

\setcounter{int}{1}
\loop
\theint
\addtocounter{int}{2}
\ifnum \value{int}<10
\repeat

This code does the same as @whilenum loop.

An example code:

\documentclass{article}
\usepackage{ifthen}
\usepackage{amsmath} %\text{} command needs this package
\begin{document}
    Demonstration of @for loop:

    \makeatletter
    \@for\sun:={rising,setting}\do{The sun is \sun. }
    \makeatother

    \newcounter{int}

    @whilenum loop:
    
    \setcounter{int}{0}
    \makeatletter
    \@whilenum\value{int}<20\do
    {\stepcounter{int}\ifthenelse{\isodd{\value{int}}}{\theint\text{ }}{}}
    \makeatother
    
    "loop repeat" loop:
    
    \setcounter{int}{1}
    \loop
    \theint
    \text{ }\addtocounter{int}{2}\ifnum\value{int}<20
    \repeat
\end{document}

result