Why does printf output show up in a command prompt? - c

Question

We all know the basic Hello World program:
#include <stdio.h>
int main() {
printf("Hello World!");
return 0;
}
This will open up a command prompt and show us the "Hello, World" message.
My question is: Why? Why is the message shown in a command prompt and not in notepad for example? Why not as a Windows notification? Why is it specifically the command prompt and not something else?

Answer 1

When you “open” a file through Window’s File Explorer, the system (not necessarily the OS directly; various subcomponents are involved) examines the file. If it is a native Windows application, the system will execute it directly. If it is another kind of file, the system will look up an appropriate application for it. For example, if it is a Microsoft Word file, the system will start Microsoft Word with a request that it open the file.
If the file is a “command line” program, the system will start Windows Terminal (or similar program in various versions of Microsoft Windows) with a request to run the program. More specifically, it may start Windows Terminal with a request to run a particular command-line shell and to have that shell run your program.
The C language grew up in Unix-like environments where a command shell read input from a physical keyboard and write output to a physical display. In modern systems, these are usually replaced by pseudo-devices that perform the same functions in software. When the shell starts a command-line program, it creates a new process with the standard input and standard output streams of that process connected to the pseudo-device that provides the keyboard/display functions. (This is the default. You can also request a shell to start a program with input and output redirected from/to files and other devices.)
Then, when your program writes to standard output, it goes to the pseudo-device, which relays the data to the appropriate parts of the system that cause the text to be displayed in the terminal window.