在字符串C＃中查找数组元素

Question

I've been looking for a way to check a string for elements of an array and if it contains one of those elements to return the indexOf it but i'm having trouble finding a way to do this. Most of my searches end up showing me way to find the indexOf an element in an array or something similar.

As a bit of background I'm trying to create a program that takes a string from user input, splits the words of the paragraph into an array, performs certain checks on them and changes them accordingly.

For instance if the current word starts with a consonant it finds the first vowel and moves all the letters in front of it to the end of the word. This is what I tried but it prints an index of 14 so clearly something is wrong:

char[] vowelsList = new char[] { 'A', 'a', 'E', 'e', 'I', 'i', 'O', 'o', 'U', 'u' };

foreach (char vowel in vowelsList)
{
    if (currentWord.Contains(vowel))
    {
        int index = currentWord.IndexOf(vowel);
        System.Diagnostics.Debug.Write(index);
    }
}

currentWord is the word from the string from the user input that is currently being checked.

Any suggestion on different methods or keywords to try is appreciated.

EDIT

I apologise the code is actually fine, it was returning 1 and 4 because it was always receiving the input Hello and i was misinterpreting what was going on, I'm a bit of an idiot sometimes. I guess then my question would be how to get this code to only find the index of the first vowel but a poster has already stated how to do that, thank you all for the help and suggestions, most of which I have implemented.

Answer 1

You probably want to use String.IndexOfAny , which returns the zero-based index of the first occurrence in this instance of any character in a specified array of Unicode characters.

If no character is found, it returns -1 .

var index = currentWord.IndexOfAny(vowelsList);
if (index >= 0)
{ 
    // do stuff
}

Note that, as stated on MSDN, this method performs an ordinal (culture-insensitive) search, where a character is considered equivalent to another character only if their Unicode scalar value are the same. To perform a culture-sensitive search, you would need to use an overload of CompareInfo.IndexOf method, where a Unicode scalar value representing a precomposed character.

Answer 2

IndexOf returns -1 if the string doesn't contain the vowel so just use that

The zero-based index position of value if that character is found, or -1 if it is not.

int index = currentWord.IndexOf(vowel);    
if (index != -1)
{
    System.Diagnostics.Debug.Write(index);
}

And the obligatory linq answer:

vowelsList.Select(v => currentWord.IndexOf(v))
          .Where(idx => idx != -1)
          .ToList();

---

You can also half the number of iterations you have to make by using ToLower

char[] vowelsList = new char[] { 'a', 'e', 'i', 'o', 'u' };

int index = currentWord.ToLower().IndexOf(vowel);    
if (index != -1)
{
    System.Diagnostics.Debug.Write(index);
}

vowelsList.Select(v => currentWord.ToLower().IndexOf(v))
          .Where(idx => idx != -1)
          .ToList();

---

If you just want the first index you can just turn your current code into an extension method as so

private int FirstIndexOfVowel(this string s)
{
    char[] vowelsList = new char[] { 'a', 'e', 'i', 'o', 'u' };
    foreach(char v in vowelsList)
    {
        int idx = s.ToLower().IndexOf(v);
        if(idx != -1)
            return idx;
    }
    return -1;
}


int idx = currentWord.FirstIndexOfVowel();

Linq version for first index only (returns null if none found)

vowelsList.Select(v => currentWord.ToLower().IndexOf(v))
          .FirstOrDefault(idx => idx != -1);

Answer 3

Is it what you are looking for ?

   char[] vowelsList = new char[] {'A', 'a', 'E', 'e', 'I', 'i', 'O', 'o', 'U', 'u'};

        foreach (char vowel in vowelsList)
        {
            if (currentWord.Contains(vowel))
            {
                int index = currentWord.IndexOf(vowel);

                Console.WriteLine(currentWord.Substring(index, currentWord.Length - index) +
                                  currentWord.Substring(0, index));
            }
        }

Answer 4

This is what I tried but it prints an index of 14 so clearly something is wrong

You don't understand why it returns 14 even if the array doesn't contain so many characters? That means you expect that it returns the index of the char in the char[] but...

int index = currentWord.IndexOf(vowel);

returns the index of the char in the word.

This should work as expected, i use Array.IndexOf to find the index of the char in the array:

foreach (char vowel in vowelsList)
{
    if (currentWord.Contains(vowel))
    {
        int index = Array.IndexOf(vowelsList, vowel);
        //...
    }
}

Another approach is not to use foreach but a for-loop which already knows the index.

Answer 5

An example that will give you a nice and manageable overview of all vowels (or whatever your criteria for being in the array is):

var word = "Stupendous!";
char[] vowelsList = 
          new char[] { 'A', 'a', 'E', 'e', 'I', 'i', 'O', 'o', 'U', 'u' };

// Get all matches in a word, along with their positions:
var allVowels = word.Select((chr, pos) => new {chr, pos})
                    .Where(match => vowelsList.Contains(match.chr));

var positionOfFirst = allVowels.First().pos; 

Update: Tim Schmelter is probably right, so I`ll updated my answer to include the position of the characters in the array:

var allVowels = word
                 .Where(match => vowelsList.Contains(match))
                 .Select((chr, pos) => 
                           new {chr, pos, PosInArray = 
                                             Array.IndexOf(vowelsList, chr)});

var positionOfFirst = allVowels.First().PosInArray;

That last piece of code will return (for allVowels ) an IEnumerable containing the following data:

{ {chr = u, pos = 2, PosInArray = 9}, 
  {chr = e, pos = 4, PosInArray = 3}, 
  {chr = o, pos = 7, PosInArray = 7}, 
  {chr = u, pos = 8, PosInArray = 9} }