If I write putchar('\\t'); while trying to print "\t" instead of an actual tab, I get the multi character constant warning. On the other hand, if I write putchar('\\'); I get no warning. Upon looking in the ASCII table, there is no character '\\', only '\'. So why is there no warning? Why is '\\' one character but '\\t' is more than one? Can a backslash only be used to escape one following character?
\\ is one character, t is one character, so that is clearly two characters.
\\ is an escape sequence, just like \t; it means \.
If you want to print the two characters \ and t, you clearly need either two calls to putch() or a function that takes a string argument "\\t".
https://en.wikipedia.org/wiki/Escape_sequences_in_C#Table_of_escape_sequences