Question

Let’s say that I use scanf to, for example, read a character from the keyboard. After that I use printf to print the character I just read.

scanf("%c",&ch);
printf("%c",ch);

When scanf is reading the character, I must press enter to continue and run the printf, right?

And let’s say I enter ABCD with the keyboard. After that printf will print A.

But when I do this:

do {
   scanf("%c",&ch);
   printf("%c",ch);
} while (ch!='\n');

and enter ABCD with the keyboard, I assume that the printf must print A. And because A is not \n it will continue the loop, right?

But instead of this it will print ABCD. Why does this happen?

Answer 1

When you type in "ABCD\n", each scanf("%c",&ch); reads one char from the input buffer, until the newline is reached.

So after the 'A' is printed, there is still a "BCD\n" in the buffer, so that the next scanf immediately succeeds reading another char, 'B' in the next iteration of the loop.