Tikz - Dynamic Node Naming

Question

I need to dynamically create the ids of the nodes in TiKz with a counter, so that I can position the new nodes in terms of the previous ones. The counter is created as follows and gets increased for each new node:

\documentclass[10pt]{article}
\begin{document}
\thispagestyle{empty}

\newcounter{nojobs}\setcounter{nojobs}{0}

The definition of the command that creates the TiKz node dynamically is the following one (this command can get invoked as many times as required):

\newcommand{\job}[7]{
    \stepcounter{nojobs}

    \node [
        regular polygon,
        regular polygon sides=3,
        fill=headergray,
        anchor=north,
        shift={(+0.0cm,+0.0cm)},
        minimum width=\tipheight,
        minimum height=\tipheight,
        shape border rotate=90
    ]
        (__job_\value{nojobs})
        at
        (__job_\the\numexpr\value{nojobs}-1\relax.south)
    {};

}

The problem is that, whenever the command is invoked, LaTeX says:

! Undefined control sequence.
\job ...par \par \stepcounter {nojobs} \par \node 

• Is this the correct approach for the problem? Any alternative solutions?
• Can the counter variable be used in this way?
• Can the counter variable be decreased and used in the calculation of the previous node ID?

Answer 1

Your approach works -- in principle. Here are the first steps to make it work. The only real "improvement" is the use \pgfmathtruncatemacro.

\documentclass[10pt]{article}
\usepackage{tikz}
\usetikzlibrary{matrix, positioning,backgrounds,shapes}
\thispagestyle{empty}

\newcounter{nojobs}\setcounter{nojobs}{0}
\newcommand{\job}[7]{
    \stepcounter{nojobs}
    \pgfmathtruncatemacro{\ni}{\value{nojobs}}
    \pgfmathtruncatemacro{\nj}{\value{nojobs}-1}
    \node 
    [
        regular polygon,
        regular polygon sides=3,
%        fill=headergray,
        anchor=north,
        shift={(+0.0cm,+0.0cm)},
%         minimum width=\tipheight,
%         minimum height=\tipheight,
        shape border rotate=90
    ]
        (jobnode\ni)
        at
        (jobnode\nj.south)
    {#1};

}
\begin{document}
\tikz{\node (jobnode0) at (0,0) {};\job1234567\job2345678}
\end{document}

My crystal ball broke, so I had to comment out some of the options which one does not know without a compilable MWE.

EDIT: I cut of the .0 in the floating point numbers returned in an earlier version of my answer, using the comments to this question.