Answer by egreg for Use a variable in foreach

You're redefining \end at the same grouping level as the \end{tikzpicture} instruction. So when TeX sees \end{tikzpicture} it will obey your redefinition and replace it with

2.0{tikzpicture}

Can you see why your choice isn't really good?

Use a different name, there's plenty of them, for instance \END. But it should really be

\pgfmathtruncatemacro{\END}{2}

otherwise you will get 2.0 and the loop would use floating point numbers.

Example:

\documentclass{article}\usepackage{tikz}\begin{document}\begin{tikzpicture}  \pgfmathtruncatemacro\END{2}  \foreach \x in {0,...,\END}{       \draw(\x,1)--(\x,0);  }\end{tikzpicture}\end{document}