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[SOLVED] string to BCD and back again

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bwend

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I have a C programming task to do, and need some assistance with this part.
I have a string, for example: 02e0

I need to convert this string to BCD, then back into its original format, by subtracting '0' and shifting.

I run into problems when hitting the 'e', my method sees this:
101 - 48, and hence stores '5' (decimal 53). However I need to retrieve this character back as its original hex 'e' value.

Does anyone have any suggestions?
 

the +-48 trick is used with numbers because it can convert a value 0-9 to a char representation 0-9 and vice versa,
you are obviously trying to convert a hex value of 0-15 (0-f) to the char 0-9 and a-f and vice versa.
You can use a condition that checks if the number is <=57 (which is char 9) and if true subtract the value 48 ,
if false then you have to subtract 55 so that a becomes 10, b 11 etc.

Then use a condition in the reverse direction too, if <=9 then add 48 else add 55.

Alex

---------- Post added at 21:28 ---------- Previous post was at 21:20 ----------

One small correction, +-55 is for letters A-F , for a-f you have to use +-87

Alex
 
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    bwend

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Ah yes, another 'Doh!' moment. Thank you for your succinct (and absolutely correct) reply.
 

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