Write a regular expression for fixed$-$point, floating point numbers. Assume that there is always at least one digit on either side of the decimal point. For example, $0\mathrm{.}0,0\mathrm{.}12,5\mathrm{.}0,11\mathrm{.}234.$ Use character classes as explained at the end of section $3\mathrm{.}1$ in the book.