This issue is a duplicate of bug #50355.

A related issue is bug #49945: `/*` after `//` incorrectly switching on multiline comment coloring.  For example:

//  This /* should not start comment coloring,
    but it does. */

Nano's colorizing regexes are simply not powerful enough to express that `/*` in a string or after `//` should not start comment coloring.  Can't be helped.

first opened here: https://bugs.gentoo.org/show_bug.cgi?id=939479

When opening a .c file in nano, /* and */ get treated as comment markers, even in string literals.

For example, when opening this as a .c file:

char *x = "/*"; char *y = "*/";

#include <stdio.h>

int main()
{
    printf("%s %s\n", x, y);
}

The syntax highlighter treats everything between the /* and the */ as a comment,
even though this is incorrect.