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tolower done manually

Posted on 1999-01-20
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Last Modified: 2010-04-02
I know that ctype.h has a tolower function.

If I wanted to write one manually...how is it done?

Thanks!
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Question by:Tom Knowlton
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8 Comments
 
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Accepted Solution

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viktornet earned 80 total points
ID: 1184652
char ToLower(char ch)
{
  if (ch >= 65 && ch <= 90)
    return (ch+32);
}

char c = 'K';

cout << ToLower(c);

Hope this helps...

-Viktor
--Ivanov
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LVL 22

Expert Comment

by:nietod
ID: 1184653
Why use ASCII numeric values?  how about

char ToLower(char ch)
   {
     if (ch >= 'A' && ch <= 'Z')
       return (ch+'a'-'A');
   }
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Expert Comment

by:viktornet
ID: 1184654
same thing :))

ch + 32 is gonna be executed faster than ch + 'a' - 'A' :))
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LVL 22

Expert Comment

by:nietod
ID: 1184655
Personally, I have no faith in optimizers, but even the worst optimizer had better catch that.
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Expert Comment

by:viktornet
ID: 1184656
with today's pentium II, there will not be much difference between the two..
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Expert Comment

by:ozo
ID: 1184657
both make an assumption about your locale
'A' is more obvious than 65 (and makes fewer assumtions about your character set)
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Author Comment

by:Tom Knowlton
ID: 1184658
Viktornet:

Your answer sounded good to me.  Haven't actually tried it yet, but I'm sure it works.

Thanks,

Tom
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Expert Comment

by:casaprog
ID: 1184659
This reminds me of the assembly days, when I used a bit operation to convert to lower or upper case.
These macro should do the work

#define ToUpper(ch) (((ch) >= 'a' && (ch) <= 'z') ? ((ch) & ~0x20) : (ch))
#define ToLower(ch) (((ch) >= 'A' && (ch) <= 'Z') ? ((ch) | 0x20) : (ch))

Regards,

Wenderson
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