How do I create a new environment with a conditional?

I'd to be able to set a value at the start of my document that sets in which chapters examples will have solutions. My attempt at this is as follows.

\newcommand{\solutionsupto}{2} \newenvironment{solution}{ \ifnum \thechapter < \solutionsupto \underline{\bf Solution} }{\fi} 

The intention here is that solutions should be displayed in chapter 1 but not chapter 2 (or later chapters).

However, I get a compilation error if I have a solution in chapter 2. For example,

\documentclass[a4paper,12pt]{book} \usepackage[british]{babel} \newcommand{\solutionsupto}{2} \newenvironment{solution}{ \ifnum\value{chapter} < \solutionsupto \underline{\bf Solution} }{\fi} \begin{document} \chapter{One} First question. \begin{solution} First answer \end{solution} \chapter{Two} Second question \end{document} 

works as expected, but

\documentclass[a4paper,12pt]{book} \usepackage[british]{babel} \newcommand{\solutionsupto}{2} \newenvironment{solution}{ \ifnum\value{chapter} < \solutionsupto \underline{\bf Solution} }{\fi} \begin{document} \chapter{One} First question. \begin{solution} First answer \end{solution} \chapter{Two} Second question \begin{solution} Second answer \end{solution} \end{document} 

results in an Incomplete \ifnum error.

On the other hand, if I replace the use of the solution environment with what I think it should evaluate to, that is

\documentclass[a4paper,12pt]{book} \usepackage[british]{babel} \newcommand{\solutionsupto}{2} \newenvironment{solution}{ \ifnum\value{chapter} < \solutionsupto \underline{\bf Solution} }{\fi} \begin{document} \chapter{One} First question. \ifnum \thechapter < \solutionsupto \underline{\bf Solution} First answer \fi \chapter{Two} Second question \ifnum \thechapter < \solutionsupto \underline{\bf Solution} Second answer \fi \end{document} 

it works exactly as expected with the first answer displayed but the second answer omitted.

Any help on this would be very much appreciated.