CODEWITHSUNDEEP
c#
Jakexx360
Jakexx360

Reputation: 25

Constantly Incrementing String

So, what I'm trying to do this something like this: (example)

a,b,c,d.. etc. aa,ab,ac.. etc. ba,bb,bc, etc.

So, this can essentially be explained as generally increasing and just printing all possible variations, starting at a. So far, I've been able to do it with one letter, starting out like this: 

for (int i = 97; i <= 122; i++)
{
    item = (char)i
}

But, I'm unable to eventually add the second letter, third letter, and so forth. Is anyone able to provide input? Thanks.

Upvotes: 1

Views: 510

Answers (4)

Tergiver
Tergiver

Reputation: 14517

Another way to look at this is that you want to count in base 26. The computer is very good at counting and since it always has to convert from base 2 (binary), which is the way it stores values, to base 10 (decimal--the number system you and I generally think in), converting to different number bases is also very easy.

There's a general base converter here https://stackoverflow.com/a/3265796/351385 which converts an array of bytes to an arbitrary base. Once you have a good understanding of number bases and can understand that code, it's a simple matter to create a base 26 counter that counts in binary, but converts to base 26 for display.

Upvotes: 0

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 727087

Since there hasn't been a solution so far that would literally "increment a string", here is one that does:

static string Increment(string s) {
    if (s.All(c => c == 'z')) {
        return new string('a', s.Length + 1);
    }
    var res = s.ToCharArray();
    var pos = res.Length - 1;
    do {
        if (res[pos] != 'z') {
            res[pos]++;
            break;
        }
        res[pos--] = 'a';
    } while (true);
    return new string(res);
}

The idea is simple: pretend that letters are your digits, and do an increment the way they teach in an elementary school. Start from the rightmost "digit", and increment it. If you hit a nine (which is 'z' in our system), move on to the prior digit; otherwise, you are done incrementing.

The obvious special case is when the "number" is composed entirely of nines. This is when your "counter" needs to roll to the next size up, and add a "digit". This special condition is checked at the beginning of the method: if the string is composed of N letters 'z', a string of N+1 letter 'a's is returned.

Here is a link to a quick demonstration of this code on ideone.

Upvotes: 2

Jason Meckley
Jason Meckley

Reputation: 7591

something to the affect of

public string IncrementString(string value)
{
    if (string.IsNullOrEmpty(value)) return "a";

    var chars = value.ToArray();
    var last = chars.Last();

    if(char.ToByte() == 122)
    return value + "a";

    return value.SubString(0, value.Length) + (char)(char.ToByte()+1);
}

you'll probably need to convert the char to a byte. That can be encapsulated in an extension method like static int ToByte(this char);

StringBuilder is a better choice when building large amounts of strings. so you may want to consider using that instead of string concatenation.

Upvotes: 0

A B
A B

Reputation: 4158

Each iteration of Your for loop is completely overwriting what is in "item" - the for loop is just assigning one character "i" at a time

If item is a String, Use something like this:

item = "";
for (int i = 97; i <= 122; i++)
{
  item += (char)i;
}

Upvotes: 0

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