Question

By default the standard input device for c++ program is

Answer 1

Your question is not clear BTW.
So, according to me the standard input device for C++ Program is Keyboard.

Answer 2

By default, the "standard input device" for a "C++ program" is "Keyboard". The standard modules and other resources provided by C++ as default for standard input output are stored in the iostream.h header file. So, it is "very important" to "make sure" that iostream.h is included in your every program while coding in C++ programming language as most of the programs we write will require the input or output functionality in it.