Why is some code from K&R not working in Code:Blocks?

Question

Some of the examples in K&R don't work in Code:Blocks when I type them exactly. For example, this program:

#include <stdio.h>
main()
{
    long nc;
    nc = 0;
    while (getchar() != EOF)
        ++nc;
    printf("%ld\n", nc);
}

When I type this code and run it, the program either freezes or doesn't do anything when I press enter.

The program below does the same thing (count characters in a string) and it works.

#include <stdio.h>
int main()
{
    char s[1000];
    int i;
    scanf("%s",s);
    for(i=0; s[i]!='\0'; ++i);
    printf("Length of string: %d",i);
    return 0;
}

Am I missing something here? Has C been changed since K&R 2nd Edition or am I doing something wrong?

You need to press CTRL+D (Unix) or CTRL+Z (Windows) in order to receive `EOF`, take a look to [End-of-file](http://en.wikipedia.org/wiki/End-of-file) — David Ranieri, Apr 20 '15 at 11:24
Apart from that, C has changed a lot since K&R. You shouldn't be reading that book to learn the language, I'd recommend finding something modern and up-to-date instead. For example, this code won't compile on C99/C11 compilers because the declaration of main() is incorrect. — Lundin, Apr 20 '15 at 11:29
What do you recommend? Is [C Primer Plus by Stephen Prata](http://www.amazon.com/gp/product/0321928423/ref=pd_lpo_sbs_dp_ss_3?pf_rd_p=1944687542&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=0321776402&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0KM2FB194G895KNJ2STE) good? — user4010936, Apr 20 '15 at 11:43
@Lundin And what material exactly in K&R isn't correct today? It's still one of the best descriptions of ISO 9899 I know. — fuz, Apr 20 '15 at 12:27
@unwind As far as I can tell, they use very different methods to get the same result so my wording is wrong. — user4010936, Apr 20 '15 at 13:02
@FUZxxl Thank you for your comment. I am half way through this book and it is only 200 pages so I will just finish it. I don't want to be switching books at this point. — user4010936, Apr 20 '15 at 13:09
@user4010936 K&R is almost completely devoid of errors but it doesn't describe any C99 or C11 extensions because these language revisions didn't exist back then. Keep that in mind. — fuz, Apr 20 '15 at 13:12
@FUZxxl Nonsense. The official errata, which is very forgiving, is several pages long. Apart from that, add the many cases of reliance on poorly-specified behavior. Then add all the errors because the book is unaware of C99 and C11. That's the factual errors. Then on top of that are the subjective errors: add the many cases of poor style, bad programming practice, dangerous programming practice. Check the code in K&R against a widely-recognized programming standard such as CERT C or MISRA C and see for yourself. — Lundin, Apr 20 '15 at 13:45
@user4010936 I haven't read any beginner books about C so I don't have any recommendations, just a big anti-recommendation for K&R. Prata made it into the [SO book recommendations](http://stackoverflow.com/questions/562303/the-definitive-c-book-guide-and-list), for what it is worth. (I've read Prata's C++ book long time ago and wouldn't really recommend that one.) — Lundin, Apr 20 '15 at 13:52

Spikatrix · Accepted Answer · 2015-04-20T11:44:37.123

6

When you press enter, you send \n into the standard input stream(and flushes other data into the stdin,if any). This character(\n) is not the same as EOF. To send EOF, press following keys combinations:

CTRL Z and then Enter in Windows.
CTRL D in Unix/Linux/OSX

edited Apr 20 '15 at 11:44

answered Apr 20 '15 at 11:26

Spikatrix

20,225
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On Windows, Ctrl-Z must be followed by Enter (although this only sends `EOF`, not `\n`). – Aasmund Eldhuset Apr 20 '15 at 11:32
@AasmundEldhuset , Right. What about CTRL+D? Should one press enter in Unix? I don't have a Unix system to test this currently. – Spikatrix Apr 20 '15 at 11:35
1

`EOF` is not a signal. – David Ranieri Apr 20 '15 at 11:35
No, it's not necessary on Unix/Linux/OSX. – Aasmund Eldhuset Apr 20 '15 at 11:35
@AlterMann , So, is it right to call `EOF` a character here? – Spikatrix Apr 20 '15 at 11:38
1

It is a condition: unequal to any valid character code – David Ranieri Apr 20 '15 at 11:41
@AlterMann , I feel that the sentence has some problem when I use "condition" instead of "signal". Do you feel like that when using "condition" in the recent revision of my answer? And I've not used either of them now. – Spikatrix Apr 20 '15 at 11:48
It could be: **the character to input to cause an EOF** – David Ranieri Apr 20 '15 at 11:51
2

On linux Ctrl-D only works when the buffer is already empty otherwise it just flushes it. Therefore unless he has pressed enter without any characters after that, he will have to press Ctrl-D twice. – Veritas Apr 20 '15 at 13:19
@CoolGuy you are the best. I was banging my head for 40 minutes thinking I was crazy. For all the praise this book gets I really expected a much diff outcome reading through it. Thank you! – Jonathan Apr 16 '16 at 00:09

score 2 · Answer 2 · answered Apr 20 '15 at 14:19

C has been changed since that book was written, but even still the code is not well-defined/valid C under any version of the standard.

If you compile using the current C standard (C11), or the previous (C99), a strictly conforming compiler (such as gcc -std=c11 -pedantic-errors) will give an error: main must return int. The old "implicit int" feature was removed in C99.

If you compile using the old C90 standard, the code invokes undefined behavior, because there is no return statement. This was allowed in C90 but it is not safe, it could cause program crashes etc. Invoking undefined behavior is always a bug, and therefore very bad practice.

(In C99, functions returning a value must have a return statement, with the exception of main(), where return can be safely omitted. So you could omit the return statement of main() if you compile as C99.)

Simply correct the code as you have already done, and it will compile in any version of the standard, without invoking undefined behavior.

All you say is true, but none of it answers the question asked. — Peter, Apr 20 '15 at 14:41
@Peter The question was "Am I missing something here? Has C been changed since K&R 2nd Edition or am I doing something wrong?" How does it not answer that question? (The question in the title doesn't make any sense since Codeblocks is an IDE) This answer could very well explain why the program freezes, since the K&R code invokes undefined behavior. Although it does indeed seem far more likely that the OP simply didn't know how to feed a EOF to the console. The answer by Cool Guy is good and should most likely be picked as the correct one. I just mentioned additional issues in the code itself. — Lundin, Apr 20 '15 at 14:43

Why is some code from K&R not working in Code:Blocks?

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