Missing characters in Greek output due to `\ttfamily`

Question

Unfortunately the next question in the series ASCII text set in Greek script when using \usepackage[greek]{babel} / Missing characters in output due to `\renewcommand{\familydefault}{\sfdefault}`

When we have a MWE like:

\documentclass[twoside]{book}

\usepackage{fontspec}
\usepackage[greek]{babel}

\setmainfont{Libertinus Sans}

\begin{document}

00027         printf({"{}JUST A PRINT STATEMENT\(\backslash\)n"{}}); \par
00027         printf({"{}Just a print statement\(\backslash\)n"{}}); \par
00028         printf({"{}Λίστα Δοκιμαστικών\(\backslash\)n"{}}); \par

  \normalfont\ttfamily%
{00027         printf({"{}JUST A PRINT STATEMENT\(\backslash\)n"{}});}\par
{00027         printf({"{}Just a print statement\(\backslash\)n"{}});}\par
{00028         printf({"{}Λίστα Δοκιμαστικών\(\backslash\)n"{}});}\par
  \normalfont%
  \normalsize%

\end{document}

The output is like:

we see that in the Momospaced part a number of Greek characters are missing, how to fix this?

Edit I used the advice from @Mico to use \setmonofont{Noto Mono}[Scale=MatchLowercase] (I actually copied his entire code), but got a strange output:

Answer 1

A monospaced font that provides the required Greek characters is Noto Mono. There must be many other suitable monospaced fonts out there.

\documentclass[twoside]{book}
\usepackage{fontspec}
\usepackage[greek]{babel}
\setmainfont{Libertinus Sans}
\setmonofont{Noto Mono}[Scale=MatchLowercase]

\begin{document}
\obeylines % to avoid having to type all those \par directives...
00027         printf({"{}JUST A PRINT STATEMENT\(\backslash\)n"{}}); 
00027         printf({"{}Just a print statement\(\backslash\)n"{}}); 
00028         printf({"{}Λίστα Δοκιμαστικών\(\backslash\)n"{}}); 
\ttfamily
00027         printf({"{}JUST A PRINT STATEMENT\(\backslash\)n"{}});
00027         printf({"{}Just a print statement\(\backslash\)n"{}});
00028         printf({"{}Λίστα Δοκιμαστικών\(\backslash\)n"{}});
\end{document}

Answer 2

You need to declare a monospaced font that supports Greek. Since your document is in sans serif, a choice might be DejaVu Sans Mono, which is also included in TeX Live. Since monospaced fonts tend to look bigger than they are, I applied a scale factor; experiment until you find the right value, but look at the screen from a distance.

\documentclass[twoside]{book}

\usepackage{fontspec}
\usepackage[greek]{babel}

\setmainfont{Libertinus Sans}
\setmonofont{DejaVu Sans Mono}[Scale=0.8]

\begin{document}

00027         printf("JUST A PRINT STATEMENT\textbackslash n"); \par
00027         printf("Just a print statement\textbackslash n"); \par
00028         printf("Λίστα Δοκιμαστικών\textbackslash n"); \par

\begin{verbatim}
00027   printf("JUST A PRINT STATEMENT\n");
00027   printf("Just a print statement\n");
00028   printf("Λίστα Δοκιμαστικών\n");
\end{verbatim}

\end{document}

Also, rather than using complicated constructions, verbatim is handier for such objects.

Answer 3

The Computer Modern Unicode fonts are clones of Knuth’s Computer Modern, like Latin Modern is, that contain Greek. So you could use

\setmainfont{CMU Serif}
\setsansfont{CMU Sans Serif}
\setmonofont{CMU Typewriter Text}

A good tip for solving bugs like this is to add \tracinglostchars=2 to the top of the file. Then TeX will tell you if the font you selected does not contain a character you’re using. By default, it silently logs a warning message to the .log file.