Want to make the following shape function in TikZ?

Question

Want to make the following shapes function in TikZ

\begin{tikzpicture}
\tikzstyle{every node}=[draw,shape=circle];
\draw (0,0)  --   (0,1)  node {1};
\draw (0,1)  --   (1,1)  node {2};
\draw (1,1)  --   (1,0)  node {3};
\draw (1,0) --    (0,0)  node {4};
\end{tikzpicture}
\begin{tikzpicture}
\tikzstyle{every node}=[draw,shape=circle];
\draw (0,0)  -- ++  (1,1)  node {1};
\draw (1,1)  -- ++  (1,-1) node {2};
\draw (0,0)  --  ++ (2,0)  node {3};
\end{tikzpicture}

Answer 1

Try to understand this code and you'll know how to draw all of them.

Start with definition of coordinates.

\coordinate (1) at (0,0,2);

creates a coordinate node (node without dimensions) named 1 at point (x,y,z)=(0,0,2). 2 means 2cm. If you need some particular unit change cm to mm, in, ... Later reference to point (0,0,2) will be done with (1). There is no need to remember its particular coordinates.

Second place circles in every coordinate and add labels to it.

    \fill (1) circle (1pt) node [below] {1};

will draw and fill a circle with radious 1pt (1 point) with center in coordinate 1. Below it a node with text 1 is placed. Because points 1 to 4 has label below and 5 to 8 has it above, it's possible to use a foreach loop.

Last, draw lines between coordinates:

\draw[dashed] (1)--(4)--(3) (4)--(8);

draws a dashed line from coordinate 1 to 4 and 3. Next places the pen on coordinate 4 and draws another line to coordinate 8.

You can use nodes (coordinates are nodes) to position other nodes. JLDiaz explained in his comments how to use calc syntax (needs \usetikzlibrary{calc} in preamble) to do it:

\coordinate (17) at ($(1)!.5!(5)$);

defines a new coordinate 17 on "the point in the line (1)-(5) which is at 50% of the distance from (1)" (the !.5! means that 50%). One you have coordinate 17 defined you can apply again \fill (17) circle (1pt) node [left] {17}; to draw the circle and label.

An alternative syntax could be

\path (1) -- (5) coordinate[pos=0.5] (17);

which means move from 1 to 5 and in pos=0.5 from this path place a coordinate node named 17. This syntax doesn't use calc library.

As an exercice: What do you think \coordinate (27) at ($(1)!.5!(7)$); does?

Before the complete code a little suggestion. If you fill intimidated by TiKZ huge documentation, take a look at some of documents recommended in

• What is the minimum one needs to know to use TikZ?

• Materials for learning TikZ

Now the complete code

\documentclass[tikz, border=2mm]{standalone}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}

\coordinate (1) at (0,0,2);
\coordinate (2) at (2,0,2);
\coordinate (3) at (2,0,0);
\coordinate (4) at (0,0,0);
\coordinate (5) at (0,2,2);
\coordinate (6) at (2,2,2);
\coordinate (7) at (2,2,0);
\coordinate (8) at (0,2,0);

\coordinate (17) at ($(1)!.5!(5)$);
\coordinate (27) at ($(1)!.5!(7)$);

\foreach \i in {1,...,4}
    \fill (\i) circle (1pt) node [below] {\i};

\foreach \i in {5,...,8}
    \fill (\i) circle (1pt) node [above] {\i};

\fill (17) circle (1pt) node [left] {17};
\fill (27) circle (1pt) node [above] {27};

\draw (1) --(2) --(3) --(7) --(6)--(5)--(8)--(7);
\draw (1)--(5) (2)--(6);
\draw[dashed] (1)--(4) --(3) (4)--(8);

\end{tikzpicture}
\end{document}