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The sample of the program is as follow:

int main(void)
{
    char input;

    printf("\nEnter phone number: ");

    while ((input = getchar()) != '\n') {

        switch (toupper(input)) {
            case 'A': case 'B': case 'C':
                printf("2");
                break;
            case 'D': case 'E': case 'F':
                printf("3");
                break;
            case 'G': case 'H': case 'I':
                printf("4");
                break;
            case 'J': case 'K': case 'L':
                printf("5");
                break;
            case 'M': case 'N': case 'O':
                printf("6");
                break;
            case 'P': case 'R': case 'S':
                printf("7");
                break;
            case 'T': case 'U': case 'V':
                printf("8");
                break;
            case 'W': case 'X': case 'Y':
                printf("9");
                break;
            default:
                putchar(input);
        }
    }

    printf("\n\n");

    return 0;
}

My question is, how on Earth does the flow here work? I can't seem to understand the path the program took. Does the char variable magically become an array? How is it that putchar() prints the entire line instead of the first character entered? How exactly does something that's supposed to get and print one character, reads and prints an entire line of characters while altering them with the switch statement? Does it test each char as its entered? But then how is the string printed as a string?

Edit: I've done some research and I read about a keyboard buffer, which seems to be the cause of my confusion. To my knowledge, getchar() and putchar() receives and outputs a single character. I'm aware that the loop asks continuously for the next "buffered" char when the getchar() comes back around, still a bit confused by I should get it, but what's more confusing is putchar(). At the end of the loop, when it breaks and goes to the condition, does it print that one character then continues and prints the other one by one with each execution of the loop? Only stopping the loop at which point the new line was read? And if so, only what was previously printed, is displayed on the screen? And then if that's the case then the printed chars would print in line next to each other with each execution, giving the illusion of a string? I need confirmation on this and also, when is the char discarded and replaced? After its printed? And at which line does it receive the next char in the buffer queue?

Alexis Wilke
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Theory Of Infinity
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    Possible duplicate of [Theory Behind getchar() and putchar() Functions](http://stackoverflow.com/questions/17552458/theory-behind-getchar-and-putchar-functions) – Ross Meikleham Apr 24 '16 at 21:33
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    Step trough your code with a debugger, you'll see that it is getting the input and printing it char by char in the loop. – Unimportant Apr 24 '16 at 21:34
  • Please explain, what exactly is the problem. You seem to run the program and observe output that is different from what you expect. So please, show what you expect and what you actually got. – rpy Apr 24 '16 at 21:34
  • I suggest you find a good book to learn from – Andreas DM Apr 24 '16 at 21:34
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    Hint, your outer loop `while ((input = getchar()) != '\n')` reads each character one at a time until it is equal to what? `'\n'` (where is that located?) – David C. Rankin Apr 24 '16 at 21:50
  • I expect to see one char printed then a request for another, or else just one char printed; the first of how much ever was entered – Theory Of Infinity Apr 24 '16 at 22:08
  • Ponder this: why do you see *anything* on your screen when you type into a terminal window? Why are you able to backspace to correct errors in your typing before you press enter, but not after? The command prompt is provided by another regular program -- it has the same tools to work with that your program does. – John Bollinger Apr 24 '16 at 23:31

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