subtracting letters in c

Question

I would like to know how to "subtract letters" in C: I mean, I have 2 letters, 'a' and 'c' and i want to execute 'c'-'a'='b' which is 3-1=2. How is it possible to obtain the same behaviour in C? I can conversion Letters->Numbers but how to manage the limited lenght of the alphabet? Thank you.

Accepted Answer

you can treat the letters as numbers and then add the letter `'a'` back to normalize it

so

```
char c1 = 'a';
char c2 = 'c';
int diff = c2 - c1; //'c' - 'a' = 2
char ans = diff + 'a' - 1; //add 'a' and subtract 1 to normalize it
```

If you want the number difference just use `diff` from my answer (`ans` will give you the letter).

This will not wrap around so

```
'a' - 'b' 
```

will result in `-1` (or the character before a)

If you want to handle negatives with a wrap you have to check it

```
int diff = c2 - c1;
char ans;
diff > 0 ? ans = diff + 'a' - 1 : 'z' + diff + 1; 
```

This will give:

- `'z'` for `'b'-'c'`

- `'y'` for `'b'-'d'`

subtracting letters in c

Solution

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