"By default, input is being given with the keyboard, and output is displayed on your screen. Your keyboard is your "standard input" (stdin) device, and the screen is the "standard output" (stdout) device." (Google)
I am impressed to see the clever way (Post#4) of displaying 64-bit integer data on the Serial Monitor of Arduino IDE using printf() function while Serial.print() is unable to do it.
Arduino DUE Board contains a very powerful 32-bit processor (SAM3X8E) which is comparable to Intel 80386DX processor.
The mechanism through which the Computer Monitor is a stdout device to an 80386DX-based Computer, it is same mechanism that makes the Serial Monitor of Arduino IDE a stdout device for the SAM3X8E-based Microcomputer (the Arduino DUE).
printf(" bignum0 = 0x%llx\n", bignum0); // this statement works.
printf("Arduino"); //this statement does not work (does not show Arduino on Serial Monitor).