The C programming language Second Edition practice 1-9

Question

The specific question is this: the user enters the text, for example, if the user enters

hello (spaces) (spaces) world

The output that the user gets is

hello (space) world.

The following is my code, the adjustment of the number of spaces can be achieved, I am a bit confused because my output will eat the first letter. I want to know why this will happen.

The code:

#include <stdio.h>

int main() {

    int characters = 0;
    while ((characters = getchar()) != EOF) {

        if (characters != ' ') {
            putchar(characters);
        }

        if (characters == ' ') {
            while ((characters = getchar()) == ' ');
            putchar(' ');
        }

    }
}

The output:

Hello  world  world  world
Hello orld orld orld

Please include the output in the question (copy-and-pasted if possible) as text, formatted as code (use the {} button). Images of text are discouraged. — Keith Thompson
– Keith Thompson, Commented Dec 19, 2018 at 4:02
Please post console output as code formatted text, not images — Mad Physicist
– Mad Physicist, Commented Dec 19, 2018 at 4:02
Sorry, it's the first time I use stackoverflow, I will pay attention to it next time. — Harry
– Harry, Commented Dec 19, 2018 at 4:09

David Schwartz · Accepted Answer · 2018-12-19 04:01:08Z

2

    if (characters == ' '){
        while ((characters = getchar()) == ' ');
        putchar(' ');
    }

This code will keep eating characters until it eats a non-space. But you don't want to eat any non-spaces. A simple fix:

    if (characters == ' '){
        while ((characters = getchar()) == ' ');
        putchar(' ');
        putchar(characters);
    }

Now you eat characters until you eat a non-space, then you output one space, then you output the non-space character you ate.

answered Dec 19, 2018 at 4:01

David Schwartz

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2 Comments

Mad Physicist Over a year ago

You also need to check for EOF here. Probably don't want to print that.

David C. Rankin Over a year ago

May also want an else break; after that check on EOF to prevent calling getchar() again on a stream with EOF.

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