Problem with \newcommand{\nal}{\end{align*}}

Question

Why do these newcommands result in error when used?

\newcommand{\bal}{\begin{align*}}
\newcommand{\nal}{\end{align*}}

Answer 1

Here is some code which does exactly what you want. As you can read in the answers of the dupe question, this is not really good advice. There is very little gain in obfuscating your code like this. You just safe very few key-strokes which are not even needed when using a good TeX editor. Btw., like this you would have to define new macros for the other align environment... so why invent the wheel a second time?

% arara: pdflatex

\documentclass{article}
\usepackage{mathtools}
\def\bal#1\nal{\begin{align*}#1\end{align*}}

\begin{document}
 \bal
 a&=c\\
 b&=d
 \nal
\end{document}