How to set value of alphabet letter? C++

Question

Well, I have to make a task, that will sort elements of array in UNIQUE way.

So, for example, if I input 1st string: BOB, I have to do: 2+15+2 (because of their positioning in the alphabet) and then divide by amount of chars /3 and do that for all inputted strings and then sort them by highest to lowest. :)

My question is, how do I set value 1,2,3,4,5... for A,B,C,D,E..... (only big letters).

Thank you.

he means he has homework to do, and doesn't want to do it... — Gonçalo Vieira, Feb 28 '13 at 14:38
Well, considering I'm a beginner in C++, I wouldn't go and try to solve some complex and advanced challenges.. — John Smith, Feb 28 '13 at 14:43
Hi @JohnSmith, as other comments have suggested, if this is homework please mark it as so with the [tag:homework] tag. Additionally, it's also recommended to post "what you've already got / tried". If you haven't got anything yet, maybe some pseudo code would be useful. — Richard, Feb 28 '13 at 15:51

score 2 · Answer 1 · answered Feb 28 '13 at 14:35

2

If the underlying encoding is seuqential, such as ascii.

letter - 'A' + 1

A more robust and general approach, would be to examine the char_traits of the character type.

answered Feb 28 '13 at 14:35

StoryTeller - Unslander Monica

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I don't think char_traits has what it takes for this. – R. Martinho Fernandes Feb 28 '13 at 14:42
What does the "letter" mean? – John Smith Feb 28 '13 at 14:43
@R.MartinhoFernandes, I had [char_traits::to_int_type](http://en.cppreference.com/w/cpp/string/char_traits/to_int_type) in mind. – StoryTeller - Unslander Monica Feb 28 '13 at 14:44
@JohnSmith, `letter` is the letter you are are converting to a number, of course. – StoryTeller - Unslander Monica Feb 28 '13 at 14:44
1

@StoryTeller that is basically an integral promotion. It "changes" char(0x41) to int(0x41). – R. Martinho Fernandes Feb 28 '13 at 14:45
So, let's say I have a code something like this: ` string b; cin >> b; int c; c = b - 'A' + 1; ` I get an error saying: "no match for "operator-" in 'b - 'A'" – John Smith Feb 28 '13 at 14:45
@R.MartinhoFernandes, isn't that what the OP is after? (Yeah, they only want normalize the values, but why not make it safer?). – StoryTeller - Unslander Monica Feb 28 '13 at 14:48
1

It's not safer. It does *nothing*. It does not change the value in any way. All it does is change types. – R. Martinho Fernandes Feb 28 '13 at 14:48
@JohnSmith, you get an error because a string is not a char, even if it's of length one. – StoryTeller - Unslander Monica Feb 28 '13 at 14:49
Oh, what a dummy mistake, thank you for pointing that StoryTeller. I've got one more question. To split a string to chars, can I use [0] for first char? Also, what if I got an array of strings, how do I split the string to chars then? – John Smith Feb 28 '13 at 14:52
@R.MartinhoFernandes, I know. I just don't like implicit casts. – StoryTeller - Unslander Monica Feb 28 '13 at 14:52
@JohnSmith. Yes, that will get the first character. I suggest you take a look at http://en.cppreference.com/w/. It is a very good reference for any information about the standard containers you may come across. – StoryTeller - Unslander Monica Feb 28 '13 at 14:55
I am learning C++98 right now, as I can see the website is related to C++11? – John Smith Feb 28 '13 at 14:58
@JohnSmith, it is relevant to both. The things `C++11`-related are marked as such. – StoryTeller - Unslander Monica Feb 28 '13 at 14:59
Thanks a lot for your replies. I'll ask you one last question. You've been through this and I would like to know, do you prefer to learn from eBooks or simply online by looking at articles & solving challenges? Which one is better? – John Smith Feb 28 '13 at 15:03
I added a working example of "weight" function in my answer. Enjoy! – SlavaNov Feb 28 '13 at 15:13
@JohnSmith, I prefer to learn along with a book, and than use Google when I do actual work. But considering how many poor books there are out there, I recommend you take a look at the book recommendation threads around [here](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) on SO. – StoryTeller - Unslander Monica Feb 28 '13 at 15:17

SlavaNov · Answer 2 · 2013-02-28T15:58:16.163

2

You need to define a function

int weight(const std::string& s);

And then iterate on the string char by char and do following:

w = ch - 'A' + 1

You also may check that the char is before 'A' and 'Z' or assume that.

You need to read more about ASCII

EDIT: Code of weight function (simplified):

int weight(const std::string& s) {
    int sum = 0, i = 0;
    for(i = 0; i < s.size(); i++) {
        char ch = s[i];
        sum += ch - 'A' + 1;
    }
    return sum/i;
}

edited Feb 28 '13 at 15:58

answered Feb 28 '13 at 14:36

SlavaNov

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What do you mean by "char"? – John Smith Feb 28 '13 at 14:42
Sorry, fixed, I meant "ch", which is character. ch = s[i]; where i it's your loop counter. – SlavaNov Feb 28 '13 at 14:45
Thank you. But will it work with a (std::string& s); ? One of the above answers said I must use a char. Even if the string is one letter, it won't work this way.. – John Smith Feb 28 '13 at 14:53
I added a working example of such function – SlavaNov Feb 28 '13 at 15:11

score 1 · Answer 3 · answered Feb 28 '13 at 14:39

1

If you are working on an ASCII machine, @StoryTeller's answer works. Otherwise you can create an array to map between the two:

const char letters[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
static const int numbers [ 256 ] = { 0 };

for ( size_t index = 0; index < sizeof letters; ++index ) {
    numbers [ letters [ index ] ] = index + 1;
}

assert ( numbers [ 'A' ] == 1 )
assert ( numbers [ 'Z' ] == 26 )

answered Feb 28 '13 at 14:39

Pete Kirkham

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What is an ASCII machine? – John Smith Feb 28 '13 at 14:54
@JohnSmith a machine which uses ASCII for character representation, which is most machines now-a-days. Some mainframes used EBCDIC http://en.wikipedia.org/wiki/EBCDIC which has gaps, for example between I and J, so `'J' - 'I' != 1` – Pete Kirkham Feb 28 '13 at 15:15

score 0 · Answer 4 · answered Feb 28 '13 at 14:37

0

To get the values you could use the following code:

int getValue(char which)
    {
    int ret = 0;
    switch(which)
       {
       case 'a' : ret = 1 ; break;
       case 'A' : ret = 27 ; break;
       case 'b' : ret = 2 ; break;
       case 'B' : ret = 28 ; break;
       // and so on....
       }
    return ret;
    }
  int result = 0;
  while(....)
     {
     result = result + getValue(myarray[counter]);
     }

You only need to escape the string to array and loop through it...

answered Feb 28 '13 at 14:37

Tschallacka

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He asked only for big letters and you don't need to use such table, you may just using it's ASCII value (see answers below) – SlavaNov Feb 28 '13 at 14:38
That's true... I don't need small chars, only big. And I was gonna use ASCII method except I wasn't sure how to do it. – John Smith Feb 28 '13 at 14:40

How to set value of alphabet letter? C++

4 Answers4