Atoi function implementation in C

Question

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int a=0;
 a = a*10 + str[i] - '0';

Why should '0' be subtracted from 'a*10+str[i]' to convert strings to integer?

What I have tried:

..............................

Posted 9-Dec-21 1:35am

Jahirul Sarker

Updated 9-Dec-21 2:11am

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Comments

CHill60 9-Dec-21 7:44am

Why not use the debugger to see what is happening and to work out why

Jahirul Sarker 9-Dec-21 14:13pm

I can understand it now. Thank you.

Richard MacCutchan 9-Dec-21 8:17am

If you subtract '0' from a numeric charactger, e.g. '3', it leaves the actual numeric value.

So '3' - '0' = 3

And, as suggested above, the debugger will show you how it works.

Jahirul Sarker 9-Dec-21 14:15pm

Yeah, I can understand it now.
'0' in ASCII = 48
'1' in ASCII = 49
so, 1-0 is equivalent to 49-48.
Thank you so much.

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steveb · Accepted Answer · 2021-12-09T02:11:00

Solution 1

Refer to ASCII table and you'll see that the '0' is decimal 48

Posted 9-Dec-21 2:11am

steveb

Comments

CHill60 9-Dec-21 12:09pm

Might have been nicer to also point out that '3' is decimal 51 i.e. 51 - 48 = 3 :laugh:

Jahirul Sarker 9-Dec-21 14:16pm

Yes, now it's clear to me.
'0' in ASCII = 48
'1' in ASCII = 49
so, 1-0 is equivalent to 49-48.
Thank you

CHill60 9-Dec-21 14:17pm

My pleasure

Atoi function implementation in C

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Atoi function implementation in C

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