How to Add Conditional Formatting in a \newcommand

You can put a condition directly inside a \newcommand definition. The macro checks one of its arguments and chooses which formatting to apply. For a simple comparison of text labels, the ifthen package provides \ifthenelse and \equal.

A complete example

This macro takes a status and a message. It prints urgent messages in bold red and other messages in blue.

\documentclass{article}
\usepackage{xcolor}
\usepackage{ifthen}

\newcommand{\statusmessage}[2]{%
  \ifthenelse{\equal{#1}{urgent}}%
    {\textcolor{red}{\textbf{#2}}}%
    {\textcolor{blue}{#2}}%
}

\begin{document}
\statusmessage{urgent}{The server is down.}

\statusmessage{normal}{The scheduled update is complete.}
\end{document}

The first argument, #1, is the value being tested. The second argument, #2, is the message to format. When #1 is urgent, the condition is true and the first branch is used; otherwise, the second branch is used. The % characters prevent line breaks and indentation in the definition from adding unwanted spaces to the output.

How the conditional works

The general form is:

\ifthenelse{<condition>}{<true branch>}{<false branch>}

In a macro definition, #1, #2, and so on refer to the macro’s arguments. For example, \equal{#1}{urgent} compares the first argument with the text urgent. Put the formatting commands for a match in the true branch, and the ordinary or alternative formatting in the false branch.

The example uses \textcolor and \textbf from xcolor. The condition itself comes from ifthen; if your branches only change font style, you may not need xcolor.

Adapting the pattern

To test a different argument, change the number sign and argument number. For instance, in a three-argument command, \equal{#2}{warning} tests the second argument against warning.

You can also use the condition to select different text, not just different styling:

\newcommand{\availability}[1]{%
  \ifthenelse{\equal{#1}{yes}}%
    {Available}%
    {Unavailable}%
}

This works well for a small set of simple text labels. If you want to handle several possible labels, you can nest conditionals, but a long chain quickly becomes hard to maintain. For many cases, define separate commands or use a dedicated key-value interface instead.

Common mistakes

• Leaving out a branch: \ifthenelse needs a condition, a true branch, and a false branch, in that order.
• Comparing the wrong argument: In a definition with two arguments, #1 is the first and #2 is the second. Check the command’s argument order.
• Expecting a numeric comparison: \equal is for comparing text, not for testing whether a number is greater than another. Use a numeric conditional suited to the values and packages in your document.
• Testing formatted output instead of the input: Put the test on the argument value, then apply formatting in the selected branch. This keeps the condition separate from the appearance.
• Forgetting package dependencies: \ifthenelse and \equal require ifthen; \textcolor requires a color package such as xcolor.

For a simple conditional based on an argument, this pattern keeps the decision and the formatting together in one command. If your macro needs many options or complicated comparisons, a more structured interface will usually be easier to extend.