What is the TeX equivalent for the following C# nested loop?

Question

I need a nested loop to animate PSTricks diagrams. In C# or C or C++, I usually write as follows.

int N=6;
for(int x=0; x<N; x++)
    for(int y=x+1; y<N; y++)
        Console.WriteLine("({0}, {1})",x,y);

I have attempted to do it in TeX as follows, but it does not work. :-)

\documentclass{minimal}
\usepackage{multido}

\newcommand\N{6}
\newcommand\Init{}
\newcommand\Freq{}
\begin{document}
\multido{\ix=0+1}{\N}
{
        \makeatletter
            \renewcommand\Init{\strip@pt\dimexpr\ix pt + 1pt\relax}         
            \renewcommand\Freq{\strip@pt\dimexpr\N pt - \Init pt\relax}
        \makeatother
        \multido{\iy=\Init+1}{\Freq}
        {
                (\ix, \iy)\par
        }
}
\end{document}

How to fix it?

Answer 1

\documentclass{minimal}
\usepackage{multido}

\newcommand\N{6}
\begin{document}
\multido{\ix=0+1,\ixB=1+1,\iN=5+-1}{\N}{%
  \multido{\iy=\ixB+1}{\iN}{(\ix, \iy)\endgraf}}
\end{document}

and with a counter:

\documentclass{minimal}
\usepackage{multido}
\newcommand\N{6}
\newcounter{NminusOne}
\setcounter{NminusOne}{\N}\addtocounter{NminusOne}{-1}

\begin{document}
\multido{\ix=0+1,\ixB=1+1,\iN=\theNminusOne+-1}{\N}{%
  \multido{\iy=\ixB+1}{\iN}{(\ix, \iy)\endgraf}}
\end{document}

Answer 2

You need to use \edef to expand the macro content. Using \renewcommand simply redefines the macro to the exact same content over and over again. That the \ix and \Init macros have a changing value doesn't matter here. You can't have a paragraph in \multido because it isn't defined \long. So use either \\ or hide the \par in a macro. You need also take care of spaces introduced by line breaks, e.g. after } and {. The \makeatletter and \makeatother macros must be places outside the \multido macro, otherwise it's already to late to change catcodes.

\documentclass{minimal}
\usepackage{multido}

\newcommand\N{6}
\newcommand\Init{}
\newcommand\Freq{}
\newcommand\mypar{\par}
\begin{document}
\makeatletter
\multido{\ix=0+1}{\N}{%
    \edef\Init{\strip@pt\dimexpr\ix pt + 1pt\relax}%
    \edef\Freq{\strip@pt\dimexpr\N pt - \Init pt\relax}%
    \multido{\iy=\Init+1}{\Freq}{%
        (\ix, \iy)\mypar
    }%
}
\makeatother
\end{document}

Answer 3

The following is the simplified version of Herbert's answer.

\documentclass{minimal}
\usepackage{multido}
\newcommand\N{6}


\newcounter{NTemp}
\setcounter{NTemp}{\N}

\begin{document}
\multido{\ix=0+1,\iTemp=1+1}{\N}
{
  \addtocounter{NTemp}{-1}
  \multido{\iy=\iTemp+1}{\theNTemp}
  {
    (\ix, \iy)\endgraf
  }
}
\end{document}

Answer 4

\documentclass{minimal}
\usepackage{multido}


\newcommand{\N}{6}
\newcounter{Init}
\newcounter{Freq}
\setcounter{Freq}{\N}
\newcommand\mypar{\par}

\begin{document}
\multido{\ix=0+1}{\N}
{
    \setcounter{Init}{\ix}
    \addtocounter{Init}{1}
    \addtocounter{Freq}{-1}
    \multido{\iy=\value{Init}+1}{\value{Freq}}
    {
        (\ix, \iy)\endgraf
    }
}
\end{document}