How to find the position of occurrence of character in C#?

Question

I have

string input = "XXXX-NNNN-A/N";
string[] separators = { "-", "/" };

I need to find out the position of occurrence of the seperators in the string.

The output will be

5 "-" 
10 "-"
12 "/"

How to do in C#?

Have you tried the documentation? http://msdn.microsoft.com/en-us/library/11w09h50.aspx — Matthew, May 03 '13 at 13:19
Just follow this duplicate post http://stackoverflow.com/questions/541954/how-would-you-count-occurences-of-a-string-within-a-string-c?rq=1 — Philip Gullick, May 03 '13 at 13:20
Look at string.IndexOf(...), string.IndexOfAny(...), string.LastIndexOf(...), string.LastIndexOfAny(...) methods. — Artemix, May 03 '13 at 13:21
Do those seperators have to be strings or can they be chars? — Martin Mulder, May 03 '13 at 13:26

score 2 · Answer 1 · answered May 03 '13 at 13:23

2

for (int i = 0; i < input.Length; i++)
{
    for (int j = 0; j < separators.Length; j++)
    {
        if (input[i] == separators[j])
            Console.WriteLine((i + 1) + "\"" + separators[j] + "\"");
    }
}

answered May 03 '13 at 13:23

linquize

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Wim Ombelets · Answer 2 · 2013-05-04T07:24:25.547

1

you can get a zero-based position index from the String.IndexOf() method.

edited May 04 '13 at 07:24

answered May 03 '13 at 13:19

Wim Ombelets

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ispiro · Answer 3 · 2013-05-03T13:51:58.820

1

List<int> FindThem(string theInput)
{
    List<int> theList = new List<int>();
    int i = 0;
    while (i < theInput.Length)
        if (theInput.IndexOfAny(new[] { '-', '/' }, i) >= 0)
        {
            theList.Add(theInput.IndexOfAny(new[] { '-', '/' }, i) + 1);
            i = theList.Last();
        }
        else break;
    return theList;
}

edited May 03 '13 at 13:51

answered May 03 '13 at 13:19

ispiro

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Should be `>= 0`, this way if the string starts with a separator, it will be found. – Matthew May 03 '13 at 13:28
@Matthew You caught me in mid edit. You are, of course, correct. – ispiro May 03 '13 at 13:30
Why: i = theList.Last() + 1; I think i++ would be enough. – Martin Mulder May 03 '13 at 13:35
@MartinMulder No. If i=0 and a separator was found at, say, 5 - you'll be checking from 1 and finding 5 again (If you'd use i++). – ispiro May 03 '13 at 13:37
@ispiro: Yes, but you are putting `i` (thus 0) to the list, not 5. – Martin Mulder May 03 '13 at 13:41
-1: He asks for a combination of positions + their index, not only their indexes. – Martin Mulder May 03 '13 at 13:41
@MartinMulder Corrected. As for your second comment - I don't think the OP really cares about that - I think his example was only to illustrate the question. But you may be right. – ispiro May 03 '13 at 13:47

Martin Mulder · Accepted Answer · 2013-05-03T13:44:57.490

1

Try this:

string input = "XXXX-NNNN-A/N";
char[] seperators = new[] { '/', '-' };
Dictionary<int, char> positions = new Dictionary<int,char>();
for (int i = 0; i < input.Length; i++)
    if (seperators.Contains(input[i]))
        positions.Add(i + 1, input[i]);

foreach(KeyValuePair<int, char> pair in positions)
    Console.WriteLine(pair.Key + " \"" + pair.Value + "\"");

edited May 03 '13 at 13:44

answered May 03 '13 at 13:25

Martin Mulder

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score 1 · Answer 5 · answered May 03 '13 at 14:22

1

Gotta love LINQ for stuff like this. Given this:

string input = "XXXX-NNNN-A/N";
string[] separators = {"-", "/"};

Perform the search using:

var found = input.Select((c, i) => new {c = c, i = i})
            .Where(x => separators.ToList().Contains(x.c.ToString()));

Output it for example like this:

found.ToList().ForEach(element => 
                        Console.WriteLine(element.i + " \"" + element.c + "\""));

answered May 03 '13 at 14:22

Kjartan

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Or just `("XXXX-NNNN-A/N".Select((c, i) => new { c = c, i = i }).Where(x => (new[] { "-", "/" }).ToList().Contains(x.c.ToString()))).ToList().ForEach(element => Console.WriteLine(element.i + " \"" + element.c + "\""));` :) – ispiro May 03 '13 at 14:31
Yes, possible, of course. I was, however, trying to be slightly more pedagogical here. ;) – Kjartan May 03 '13 at 14:36

joe · Answer 6 · 2013-05-03T13:54:57.693

0

Try this:

int index = 0;                                                  // Starting at first character
char[] separators = "-/".ToCharArray();
while (index < input.Length) {
    index = input.IndexOfAny(separators, index);              // Find next separator
    if (index < 0) break;
    Debug.WriteLine((index+1).ToString() + ": " + input[index]);
    index++;
}

edited May 03 '13 at 13:54

answered May 03 '13 at 13:23

joe

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Why convert your seperators into a char array every other iteration? – Martin Mulder May 03 '13 at 13:38
Why the `index.ToString()`? – Martin Mulder May 03 '13 at 13:39
@MartinMulder: `"-/".ToCharArray()` should surely be done outside the loop, that's right. – joe May 03 '13 at 13:40
@MartinMulder: `index.ToString()` because this line makes a string concatenation. `index + ":" + ...` is not intuitive for me, because index is a int. – joe May 03 '13 at 13:42
You forgot to add 1 to the index. – Martin Mulder May 03 '13 at 13:44
I did... your program will produce `4 "-"` and not `5 "-"` as requested. – Martin Mulder May 03 '13 at 13:47

How to find the position of occurrence of character in C#?

6 Answers6