# Define latex command in which argument is part of another command

Is there a way to define a LaTeX command in which an argument forms part of a command that is expanded inside the text defined by the command?

For example, here's a MNWE (Minimal Non-Working Example--it doesn't work, and that's the basis of the question):

\newcommand{\firstExclamation}{Yesiree!}
\newcommand{\secondExclamation}{No way!}

\newcommand{\firstExplanation}{You are our favorite customer.}
\newcommand{\secondExplanation}{We're all out of that product.}

\newcommand{\usesMyCommands}[1]{I said, \#1Exclamation \#1Explanation"}

Then \usesMyCommands{first} should expand into "Yesiree! You are our favorite customer.", while \usesMyCommands{second} should expand into "No way! We're all out of that product."

This question and its answer seem very relevant, as does this one, but after some experimentation, I have not figured out how to apply their lessons to my case. These questions are about how to define a command inside a command, and I want to use a command inside a command. Maybe I'm just not seeing it, though--maybe the answer is there in those answers, and I'm not realizing it.

I am sure that there is a way to do this is in raw TeX. I'm hoping not to have to descend into the TeX swamp. I respect those who routinely do so. I have also looked at this, this, and this, but hope that I do not have to understand them. :-)

\documentclass{article}

\usepackage{amsmath}

\begin{document}
\newcommand{\firstExclamation}{Yesiree!}
\newcommand{\secondExclamation}{No way!}

\newcommand{\firstExplanation}{You are our favorite customer.}
\newcommand{\secondExplanation}{We're all out of that product.}

\newcommand{\usesMyCommands}[1]{I said, \csname #1Exclamation\endcsname\ \csname#1Explanation\endcsname"}
\usesMyCommands{first}, \usesMyCommands{second}
\end{document}

• Thanks--that's great! This is going to be extremely helpful. I had tried messing around with \csname and \endcsname, but I didn't know what I was doing. Among other things, I put a backslash in front of #1. (For anyone who comes to this page without knowing what \*csname do [I didn't], this answer gives a succinct statement of their use in Ulrike's answer here, and other answers to that question describe other uses.) – Mars May 25 '18 at 0:02