Parameterized input of file inside tikz

Question

I have looked into a few threads about passing arguments to \input command but haven't found much. Any help with my current predicament (or feedback of an alternative approach) would be appreciated! My current setup (working, but not ideal) is:

Relevant part from main.tex

\begin{tikzpicture}[scale=.3]
    \input{grid}
    %some other shapes
\end{tikzpicture}

grid.tex

\draw[black!20!white] (0,0) grid (20, 20);
\fill (0,0) circle (2pt) node[below left] {(0,200)};
\fill (20,0) circle (2pt) node[below right] {(200,200)};
\fill (0,20) circle (2pt) node[above left] {(0,0)};
\fill (20,20) circle (2pt) node[above right] {(200,0)};
\fill (20,20) circle (2pt) node[above right] {(200,0)};
\tiny
\foreach \x in {20, 40, ..., 180} {
    \fill (\x/10,20) circle (2pt) node[above] {\x};
}
\foreach \y in {20, 40, ..., 180} {
    \fill (0,20-\y/10) circle (2pt) node[left] {\y};
}

Although I'd like to customize the grid. Something like -

\pgfmathsetmacro{\inc}{#1/10}
\draw[black!20!white] (0,0) grid (\inc,\inc);
\fill (0,0) circle (2pt) node[below left] {(0,#1)};
\fill (\inc,0) circle (2pt) node[below right] {(#1,#1)};
\fill (0,\inc) circle (2pt) node[above left] {(0,0)};
\fill (\inc,\inc) circle (2pt) node[above right] {(#1,0)};
\fill (\inc,\inc) circle (2pt) node[above right] {(#1,0)};
\tiny
\foreach \x in {#2, #2*2, ..., #1 - #2} {
    \fill (\x/10,\inc) circle (2pt) node[above] {\x};
}
\foreach \y in {#3, #3*2, ..., #1 - #3} {
    \fill (0,\inc-\y/10) circle (2pt) node[left] {\y};
}

And input it in main.tex as:

\begin{tikzpicture}[scale=.3]
    \input{grid}[160][10][25]
    %some other shapes
\end{tikzpicture}

or

\begin{tikzpicture}[scale=.3]
    \input{grid}[300][15][15]
    %some other shapes
\end{tikzpicture}

EDIT:

MWE as requested by @Andrew (working, but not ideal) -

main.tex:

\documentclass{exam}
\usepackage{tikz}
\begin{document}
\begin{center}
\begin{tikzpicture}[scale=.3]
    \input{grid}
\end{tikzpicture}   
\end{center}
\end{document}

grid.tex:

\draw[black!20!white] (0,0) grid (20, 20);
\fill (0,0) circle (2pt) node[below left] {(0,200)};
\fill (20,0) circle (2pt) node[below right] {(200,200)};
\fill (0,20) circle (2pt) node[above left] {(0,0)};
\fill (20,20) circle (2pt) node[above right] {(200,0)};
\fill (20,20) circle (2pt) node[above right] {(200,0)};
\tiny
\foreach \x in {20, 40, ..., 180} {
    \fill (\x/10,20) circle (2pt) node[above] {\x};
}
\foreach \y in {20, 40, ..., 180} {
    \fill (0,20-\y/10) circle (2pt) node[left] {\y};
}

EDIT 2:

Taking suggestion given by @Andrew, I have managed to define variables in the main file and use the same in grid.tex

main.tex:

\documentclass{exam}
\usepackage{tikz}
\begin{document}
\begin{center}
\begin{tikzpicture}[scale=.3]
    \def\gridsize{300}
    \def\xMarker{45}
    \def\yMarker{50}
    \input{grid}
\end{tikzpicture}   
\end{center}
\end{document}

grid.tex:

\pgfmathsetmacro\size{\gridsize/10}
\draw[black!20!white] (0,0) grid (\size,\size);
\fill (0,0) circle (2pt) node[below left] {(0,\gridsize)};
\fill (\size,0) circle (2pt) node[below right] {(\gridsize,\gridsize)};
\fill (0,\size) circle (2pt) node[above left] {(0,0)};
\fill (\size,\size) circle (2pt) node[above right] {(\gridsize,0)};
\fill (\size,\size) circle (2pt) node[above right] {(\gridsize,0)};
\tiny
\foreach \x in {0,\xMarker, ..., \gridsize} {
    \fill (\x/10,\size) circle (2pt) node[above] {\x};
}
\foreach \y in {0,\yMarker, ..., \gridsize} {
    \fill (0,\size-\y/10) circle (2pt) node[left] {\y};
}

Still hoping I can just pass the values to the file somehow :)

I don't think I can create a command since I can't put it inside tikz.

Answer 1

Do you want something like this?

\documentclass{exam}
\usepackage{tikz,xparse}
\NewDocumentCommand \mygrid { O {300} O {45} O {50} }
{
  \pgfmathsetmacro\size{#1/10}
  \draw[black!20!white] (0,0) grid (\size,\size);
  \fill (0,0) circle (2pt) node[below left] {(0,#1)};
  \fill (\size,0) circle (2pt) node[below right] {(#1,#1)};
  \fill (0,\size) circle (2pt) node[above left] {(0,0)};
  \fill (\size,\size) circle (2pt) node[above right] {(#1,0)};
  \fill (\size,\size) circle (2pt) node[above right] {(#1,0)};
  \begin{scope}[font=\tiny]
    \foreach \x in {0,#2, ..., #1} {
      \fill (\x/10,\size) circle (2pt) node[above] {\x};
    }
    \foreach \y in {0,#3, ..., #1} {
      \fill (0,\size-\y/10) circle (2pt) node[left] {\y};
    }
  \end{scope}
}
\begin{document}
\begin{center}
\begin{tikzpicture}[scale=.3]
  \mygrid[200][35][25]
\end{tikzpicture}
\begin{tikzpicture}[scale=.3]
  \mygrid
\end{tikzpicture}
\end{center}
\end{document}