EOF in Windows command prompt doesn’t terminate input stream

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This is true in almost every terminal driver. You’ll get the same behavior using Linux.

Your program isn’t actually executing the loop until \n or ^z has been entered by you at the end of a line. The terminal driver is buffering the input and it hasn’t been sent to your process until that occurs.

At the end of a line, hitting ^z (or ^d on Linux) does not cause the terminal driver to send EOF. It only makes it flush the buffer to your process (with no \n).

Hitting ^z (or ^d on Linux) at the start of a line is interpreted by the terminal as “I want to signal EOF”.

You can observe this behavior if you add the following inside your loop:

printf("%d\n",ch);

Run your program:

$ ./test
abc                      <- type "abc" and hit "enter"
97
98
99
10
abc97                    <- type "abc" and hit "^z"
98
99

To better understand this, you have to realize that EOF is not a character. ^z is a user command for the terminal itself. Because the terminal is responsible for taking user input and passing it to processes, this gets tricky and thus the confusion.

A way to see this is by hitting ^v then hitting ^z as input to your program.

^v is another terminal command that tells the terminal, “Hey, the next thing I type – don’t interpret that as a terminal command; pass it to the process’ input instead”.

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