Verify that the expression getchar() != EOF is 0 or 1, ctrl-D gets "0D", not "0"

Question

i am learning The C Programming Language" by Kernighan and Ritchie (2nd edition), Exercise 1.06 on page 17

my question is why everytime i enter ctrl-d, it prints "0D", not "0", my computer is iMAC m1 chip. thanks

#include <stdio.h>

main()
{
    printf("%d\n", getchar() != EOF);
}

Might be a duplicate: https://stackoverflow.com/questions/21364313/signal-eof-in-mac-osx-terminal. But I wouldn't know, since I would never even consider a mac for (the purpose of learning) programming... — Lundin, Aug 23 '23 at 06:54

score 4 · Answer 1 · answered Aug 23 '23 at 07:21

The reason for your observations is when you type Ctrl-D the terminal echoes ^D and 2 backspaces (BS) and returns 4 immediately. The effect is the cursor is on the ^ character on the screen and when printf outputs 0 and a newline, the 0 overwrites the ^ and the newline is converted to a CR+LF, causing the cursor to go to the beginning of the next line.

You can modify your program to avoid this problem by printing a newline before the %d conversion:

#include <stdio.h>

int main(void) {
    printf("\n%d\n", getchar() != EOF);
    return 0;
}

Output:

^D
0

Verify that the expression getchar() != EOF is 0 or 1, ctrl-D gets "0D", not "0"

1 Answers1