using includegraphics conditionally

Question

I want to print a different logo sequentially for 4 years, and then resuse them. My script is not working... any idea?

\documentclass{article}
\usepackage{pgf,calculator,ifthen}
\MODULO{\year}{4}{\ye}
\newcommand{\autologo}{\ifcase\ye\relax logotp0.pdf\or logotp1.pdf\or logotp2.pdf\else logotp3.pdf\fi}
\newcommand{\auteloge}{\ifcase\ye\relax example-image-a\or example-image-b\or example-image-c\else example-image-d\fi}
\begin{document}
\includegraphics[scale=0.5]{logotp2.pdf}  % works for the 4 image files...
\includegraphics[scale=0.5]{\auteloge}   %works
\includegraphics[scale=0.5]{\autologo}    % error argument of \@firstofone
\end{document}

Answer 1

You have spurious spaces appended to the file names:

\documentclass{article}
\usepackage{pgf,calculator,ifthen}
\MODULO{\year}{4}{\ye}
%\newcommand{\autologo}{\ifcase\ye\relax logotp0.pdf \or logotp1.pdf  \or logotp2.pdf  \else logotp3.pdf \fi}
 \newcommand{\autologo}{\ifcase\ye\relax logotp0.pdf\or logotp1.pdf\or logotp2.pdf\else logotp3.pdf\fi}

\begin{document}
\includegraphics[scale=0.5]{logotp2.pdf}  % works...
\includegraphics[scale=0.5]{\autologo}    % but I want something like this
\end{document}

I replaced your image names with example-images and it worked:

\documentclass{article}
\usepackage{pgf,calculator,ifthen}
\usepackage{duckuments}
\MODULO{\year}{4}{\ye}
\newcommand{\autologo}{%
  \ifcase\ye\relax
      example-image-a%
  \or example-image-b%
  \or example-image-c%
  \else example-image%
  \fi}

\begin{document}
\pagenumbering{gobble}
\includegraphics[scale=1]{example-image-duck}  % works...
\includegraphics[scale=0.5]{\autologo}    % but I want something like this
\end{document}

TeX ignores spaces after the control sequence names (\relax, \or, and \else, for example), but not after normal characters, so with your previous code \includegraphics failed because it didn't find a file named logotp2.pdf .<extension>.

Edit:

Since we're apparently stuck here, let me suggest a more robust approach using expl3:

\documentclass{article}
\usepackage{pgf,calculator,ifthen}

% Copy this to the preamble of your document
\usepackage{xparse}
\ExplSyntaxOn
\seq_new:N \jom_logos
\NewDocumentCommand\DefineAutologo
  { m }
  {
    \seq_set_from_clist:Nn \jom_logos { #1 }
  }
\NewExpandableDocumentCommand\UseAutologo
  { m }
  {
    \seq_item:Nn \jom_logos { #1 }
  }
\ExplSyntaxOff

% Use this to set the images you want to use
\DefineAutologo{
  example-image-a,
  example-image-b,
  example-image-c,
  example-image
}

\MODULO{\year}{4}{\ye}

\begin{document}
\pagenumbering{gobble}
\includegraphics[scale=0.5]{example-image}  % works...
% Include the image with `\UseAutologo{<image-number>}`
\includegraphics[scale=0.5]{\UseAutologo{\ye}}    % but I want something like this
\end{document}