Detect keyboard input without return key in c++?

write a program that will receive the characters from the keyboard (0's , l's or any other character) until it detects an HDLC flag. Upon detection of the first flag, the program will continue to receive the characters from the keyboard and shows them on the screen until a flag is detected again. The program prints to the screen that the end flag has been detected and that the is the information keyed in between the two flags. No Carriage Return is allowed as part of your input at any time.