getchar() != ' ' and getchar() = ' '

Question

I am having trouble understanding what getchar() != ' ' and getchar() = ' ' are doing in my code. Why do there need to be opposites. The user may input extra spaces between the first name and last, and before the first name and after the last name.

#include <stdio.h>

int main(void) {

    char c, initial;

    printf("Enter a first and last name: ");
    scanf(" %c", &initial);
    printf("%c\n", initial);
    while ((c = getchar()) != ' ')
        ;

    while ((c = getchar()) == ' ')
        ;

    do {
        putchar(c);
    } while ((c = getchar()) != '\n' && c != ' ');

    printf(", %c.\n", initial);

    return 0;
}

Without even looking at your code, I can tell you that any appearance of `getchar() = ' '` serves only one purpose: to cause compilation to fail. — John Bollinger, Dec 26 '19 at 18:01
In any case, if it's your code then how do you not at least know what purposes its various bits are *supposed* to serve? — John Bollinger, Dec 26 '19 at 18:02
It's not my code. I am looking at someone else's answer for the same exercise in a programming textbook. The code does not fail though and works perfectly. — Nick, Dec 26 '19 at 18:10
@Nick "what getchar() != ' ' and getchar() = ' ' are doing in my code" Remove them immediately! :) — Vlad from Moscow, Dec 26 '19 at 18:10
your question states: `and getchar() = ' '` which would not compile. However the code is correct with: `while ((c = getchar()) == ' ')` — user3629249, Dec 26 '19 at 18:53

Vlad from Moscow · Accepted Answer · 2019-12-26T18:52:46.393

2

In this code snippet

scanf(" %c", &initial);
// printf("%c\n", initial); <== remove this statement
while ((c = getchar()) != ' ')
    ;

The first letter of the first name is read and other letters are skipped.

This loop

while ((c = getchar()) == ' ')
    ;

skips spaces between the first name and the second name.

This loop

do {
    putchar(c);
} while ((c = getchar()) != '\n' && c != ' ');

outputs all letters of the second name.

And at last the first letter of the first name is outputted after the full second name.

So if you entered for example

Nick     Fisher

then the output should be

Fisher, N.

Take into account that you should remove the statement

printf("%c\n", initial);

it is a redundant statement.

edited Dec 26 '19 at 18:52

answered Dec 26 '19 at 18:16

Vlad from Moscow

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thank you very very much! This explains it perfectly – Nick Dec 26 '19 at 18:34
The original code won't work as intended if there are leading white-space characters in the line entered. – Lxer Lx Dec 26 '19 at 18:46
1

@LxerLx Why did you decide so? The leading white spaces are skipped. – Vlad from Moscow Dec 26 '19 at 18:47
the output is not what will actually happen. The first line of the output will be the initial due to: `printf("%c\n", initial);` – user3629249 Dec 26 '19 at 18:51
@VladfromMoscow You are right. I've overlooked the space before `%c`. – Lxer Lx Dec 26 '19 at 18:59
Yes the redundant statement was added so I could try to figure out what was going on. – Nick Dec 26 '19 at 19:01

score 0 · Answer 2 · answered Dec 26 '19 at 18:45

0

regarding:

while ((c = getchar()) != ' ')
    ;

while ((c = getchar()) == ' ')
    ;

the first while() loop consumes the rest of the first name

the second while() loop consumes the spaces between the first and last name.

answered Dec 26 '19 at 18:45

user3629249

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score 0 · Answer 3 · edited Jan 22 '21 at 07:31

0

isn't there a problem using a char for initial and then writing a lot of characters into it? I think your using not allocated memory for the name.
And the first printf("%c\n", initial); should generate an output of the first character entered.

Soooo...
Input:
Nick Fisher

Output:
N
Fisher, N.

or:

Fisher, N.
or:
program crash because of forbidden memory access

regards André

edited Jan 22 '21 at 07:31

Martin Brisiak

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answered Jan 21 '21 at 18:05

derAnder0815

1

getchar() != ' ' and getchar() = ' '

3 Answers3