How to clean up Serial port buffer

Projects Programming
3 
Serial.readBytesUntil('\n\r',buf, MAX)

A single char is enclosed in single quotes. Two or more chars make a string, which must be included in double quotes.

I tried compiling this simple test sketch with verbose compilation enabled:

char ch = '\n\r';

void setup() {}
void loop() {}

I got this (buried inside a flood of other messages):

sketch_oct07a.cpp:4:11: warning: multi-character character constant
sketch_oct07a.cpp:4:11: warning: overflow in implicit constant conversion