Why does this code work?

This is a discussion on Why does this code work? within the C Programming forums, part of the General Programming Boards category; This very small program is an example from a book on C programming I'm currently working through. It runs perfectly. ...

  1. #1
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    Why does this code work?

    This very small program is an example from a book on C programming I'm currently working through. It runs perfectly. I understand most of it. That being said, I cannot understand why the initialization of num does not cause an error.

    Code:
    #include <stdio.h>
    
    long	factorial( long num );
    
    int main (int argc, const char * argv[]) {
    	long	num = 5L;
    	
    	printf( "%ld factorial is %ld.", num,
               factorial( num ) );
    	
    	return 0;
    }
    
    
    long	factorial( long num ) {
    	if ( num > 1 )
    		num *= factorial( num - 1 );
    	
    	return( num );
    }

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    Quote Originally Posted by Whitewings View Post
    This very small program is an example from a book on C programming I'm currently working through. It runs perfectly. I understand most of it. That being said, I cannot understand why the initialization of num does not cause an error.

    Code:
    #include <stdio.h>
    
    long factorial( long num );
    
    int main (int argc, const char * argv[]) {
      long num = 5L;
    
      printf( "%ld factorial is %ld.", num,
        factorial( num ) );
    	
      return 0;
    }
    
    long factorial( long num ) {
      if ( num > 1 )
        num *= factorial( num - 1 );
       return( num );
    }
    Although it may be of no consequence on most compilers, some older ones will balk at tabs between the type and variable names...

    Why would.... long num = 5L;.... not work? The L suffix merely tells the compiler to treat the number 5 as a long int.

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    Thank you. I had forgotten the significance of the L suffix.

  4. #4
    and the hat of wrongness Salem's Avatar
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    > Although it may be of no consequence on most compilers, some older ones will balk at tabs between the type and variable names...
    *boggle* - which brain-damaged compiler would barf so badly on white space?
    I've used some pretty ropey compilers in the past, but none have failed that badly.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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    Quote Originally Posted by Whitewings View Post
    This very small program is an example from a book on C programming I'm currently working through. It runs perfectly. I understand most of it. That being said, I cannot understand why the initialization of num does not cause an error.
    When you declare something like, long num, int is implied. This is guaranteed by the standard.

    EDIT: C99 6.7.2.2/5
    Last edited by AndrewHunter; 08-16-2011 at 10:46 AM.
    Quote Originally Posted by anduril462 View Post
    Now, please, for the love of all things good and holy, think about what you're doing! Don't just run around willy-nilly, coding like a drunk two-year-old....
    Quote Originally Posted by quzah View Post
    ..... Just don't be surprised when I say you aren't using standard C anymore, and as such,are off in your own little universe that I will completely disregard.
    Warning: Some or all of my posted code may be non-standard and as such should not be used and in no case looked at.

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    Quote Originally Posted by Salem View Post
    > Although it may be of no consequence on most compilers, some older ones will balk at tabs between the type and variable names...
    *boggle* - which brain-damaged compiler would barf so badly on white space?
    I've used some pretty ropey compilers in the past, but none have failed that badly.
    Oh gees now you want me to go and find that? I don't remember the name... but it had a ton of other problems too.

  7. #7
    and the hat of wrongness Salem's Avatar
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    I'm guessing it was for some embedded C compiler for some rather obscure bit of hardware.
    Your average desktop user (especially a student) using a popular modern compiler isn't likely to find an actual compiler bug.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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    Quote Originally Posted by CommonTater
    Oh gees now you want me to go and find that? I don't remember the name... but it had a ton of other problems too.
    Heh, I'm curious as to why you mentioned that little piece of trivia out of the blue.
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    Quote Originally Posted by laserlight View Post
    Heh, I'm curious as to why you mentioned that little piece of trivia out of the blue.
    Before settling on Pelles C I'll bet I tried just about every language/compiler available at the time. A lot --and I do mean a LOT-- of it was pure crap. Switching from a murdered language (Pascal) to something else was neither easy nor graceful. I spent most of a year looking for something that actually did what I expected... Found some really strange stuff along the way.


    @Salem ... then you should visit the Pelles C forums... they have an entire section for bug reports and people do find things... Fortunately most of them are minor or easily worked around.

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