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Re: To reverse the digits of a numeral

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  Re: To reverse the digits of a numeral Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-14 02:09 +0100

#65531 — Re: To reverse the digits of a numeral

ram@zedat.fu-berlin.de (Stefan Ram) writes:

>   To me, it makes non sense to "reverse the digits of a numeral".
>
>   When you have stored a numeral, you can read it in any order you
>   like. It has no direction! Therefore, it can't be "reversed".

I don't understand this.  In this usage of the word numeral it's a
sequence of digits (also sometimes confusingly called numerals).  A
sequence has an order and, if it's finite, can be reversed.

> #include <stdio.h>  /* putchar */
> #include <string.h> /* strlen  */
> #include <stddef.h> /* size_t  */
>
> int main( void ) 
> { char const * const numeral = "123";
>   size_t const length = strlen( numeral );
>   char const * const numeral_top = numeral + length;
>   
>   for( char const * p = numeral; p < numeral_top; ++p )
>   putchar( *p ); putchar( '\n' ); 
>
>   for( char const * p = numeral_top - 1; p >= numeral; --p )
>   putchar( *p ); putchar( '\n' ); }

That's undefined.  I'd probably write

  const char *p = numeral_top;
  while (p > numeral)
    putchar(*--p);

but there are obviously loads of alternatives.

<snip>
-- 
Ben.

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