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How atoi() works - char to int?

+3 votes
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In K&R I found a piece of code which showed how atoi() works. It said like s[i] - '0' will give a numeric value of the character.

Can someone please explain it to me. I tried to search around but they only explain it with integers and not with characters. Say you are given s[i] = 'C'.

posted Oct 22, 2014 by anonymous

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1 Answer

+1 vote

I would suggest you to go through the manual page of atoi() "man atoi".

Here is my answer:
As per manual page of atoi() it convert a sting to an integer.
It will only convert a string which has an integer value i.e
1> char str1[10] = "123456789"; //string which contains integer value
2> char str2[10] = "abcD"; //string with non integer values.
So atoi(str1); // will give you a integer value 123456789 but
atoi(str2); // it will give any value, because atoi() won’t detect error.

So basically atoi() is used to convert a string which has valid integer value. It won't work same as on other values.

Hope you understand now. :)

answer Oct 23, 2014 by Arshad Khan
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