Home/ Questions/Q 902561
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-15T15:44:13+00:00

Possible Duplicate: Char to int conversion in C. I remember learning in a course

  • 0

Possible Duplicate:
Char to int conversion in C.

I remember learning in a course a long time ago that converting from an ASCII char to an int by subtracting ‘0’ is bad.

For example:

int converted;
char ascii = '8';

converted = ascii - '0';

Why is this considered a bad practice? Is it because some systems don’t use ASCII? The question has been bugging me for a long time.

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    While you probably shouldn’t use this as part of a hand rolled strtol (that’s what the standard library is for) there is nothing wrong with this technique for converting a single digit to its value. It’s simple and clear, even idiomatic. You should, though, add range checking if you are not absolutely certain that the given char is in range.

    It’s a C language guarantee that this works.

    5.2.1/3 says:

    In both the source and execution basic character sets, the value of each character after 0 in the above list [includes the sequence: 0,1,2,3,4,5,6,7,8,9] shall be one greater that the value of the previous.

    Character sets may exist where this isn’t true but they can’t be used as either source or execution character sets in any C implementation.

    • 0