How to search for a specific string in an string array in C# 3.0

Question

I'm trying to search for a string in a string array in C# but I'm not sure how. So, if the array has 50 elements, most of them null, how would I go about searching for a string in the array? For example:

string[] this_array;
this_array = new string[50];
this_array[1] = "One, Two, Three";
this_array[2] = "Foo, Bar, Five";
this_array[3] = null;

How would I go about searching for "Five" in this_array? I understand I have to use a for loop, I'm just not sure of the actual code. I have to find the exact index so I cannot obtain a boolean.

Any help would be much appreciated!
Jamie

Update: Here's my, very incomplete code, so far:

for (array_number = 1; array_number < this_array.Length; array_number++)
{
  //no idea what to put here :S
}

What have you tried so far? Is this home work? Have you tried using a for loop? If yes, where exactly are you stuck? :) — Jude Cooray
– Jude Cooray, Commented Sep 14, 2011 at 12:59
Why do you have multiple values in a single element of the array. That is a horrible design decision. — Security Hound
– Security Hound, Commented Sep 14, 2011 at 13:04
I feel you haven't actually bothered searching on a search engine for this sort of problem before posting. I've just typed in a question in google about finding text in a string and I'm swimming in correct results. You should also look up how a for loop works. — Stuart Thomson
– Stuart Thomson, Commented Sep 14, 2011 at 13:07
I admit it's horrible but I'm very new to C#. And yes, it's homework. — Jamie
– Jamie, Commented Sep 14, 2011 at 13:08

Fabio Milheiro · Accepted Answer · 2011-09-15 00:22:36Z

2

Use Linq. It's the easiest and less error prone way.

Add a using statement to the top:

using System.Linq;

And search like this.

var result = this_array.Where(x => x != null && x.Contains("string to compare"));

if (result != null) System.Writeln(result.First());

edited Sep 15, 2011 at 0:22

answered Sep 14, 2011 at 13:02

Fabio Milheiro

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7 Comments

musefan Over a year ago

OP is looking for a "contains" search not an exact search

Nick A Miller Over a year ago

Works only where the whole string matches the search string - would not find "Five", as described in the question.

Marc Over a year ago

@pstrjds: C# 3.0 != .NET 3.0. C# 3 release coincided with .NET 3.5, which does include LINQ.

pstrjds Over a year ago

downvoted because is does not answer the question and uses Linq, which (unless I am mistaken) is not available in .Net 3.0, which this question is clearly tagged as and is even stated in the question title.

pstrjds Over a year ago

@Marc My bad, I just googled and saw you are correct about that. I thought the C# 3.0 equated to .Net 3.0. Glad there is consistency in the numbering :) The answer still doesn't handle the contains portion of the question though.

|

pstrjds · Accepted Answer · 2011-09-14 13:07:06Z

1

Here is some sample code for you. This will find the first index for a matching entry.

int foundIndex = -1;
for(int i=0; i < this_array.Length; ++i)
{
    if (!string.IsNullOrEmpty(this_array[i]) && this_array[i].Contains(searchString))
    {
        foundIndex = i;
        break;
    }
}

answered Sep 14, 2011 at 13:07

pstrjds

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Comments

musefan · Accepted Answer · 2011-09-14 13:13:23Z

0

You could try this...

int index = -1;
string find = "Five";

for(int i = 0; i < this_array.Length; i++)
{
   if(string.IsNullOrEmpty(this_array[i]))
      continue;
   if(this_array[i].ToLowerInvariant().Contains(find.ToLowerInvariant()))
   {
      index = i;
      break;
   }
}

NOTE: My search is case-insensitive. If you care about the casing of characters the remove both instances of .ToLowerInvariant()

edited Sep 14, 2011 at 13:13

answered Sep 14, 2011 at 13:01

musefan

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7 Comments

pstrjds Over a year ago

you would probably want to perform the ToLowerInvariant on the find string as well.

Security Hound Over a year ago

Why on earth would you not just add (!string.IsNullOrEmpty(this_array[i])) to the Contains conditional. Of course there are better ways like Fabio suggested. I have to vote this down because of the poor techique.

musefan Over a year ago

@pstrjds, thanks I meant to put that but must have forgot by the time I typed all the rest (need Intellisense here!)

Jamie Over a year ago

Thanks @musefan but that didn't seem to work - it processes fine (i.e. there aren't any errors outputted) but it doesn't find the string.

pstrjds Over a year ago

If you do care about this remaining case-insensitive, it would be a good idea to perform the ToLowerInvariant on the find string outside the bounds of the for loop, since it's value is constant throughout the loop. There is no need to repeatedly perform that operation in the loop.

|

xr280xr · Accepted Answer · 2011-09-14 13:46:12Z

0

Since this was homework, I'd recommend you familiarize yourself with the methods available in the String class:

String Methods

MSDN is your friend.

answered Sep 14, 2011 at 13:46

xr280xr

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Comments

Schroedingers Cat · Accepted Answer · 2011-09-14 13:01:53Z

-1

for(int i=1;i<this_array.length;i++)
    if(this_array[i]!=null)
        if(this_array[i].indexOf("Five")>-1
            return i;

That is roughtly c# code - I may have made some minor errors. But surely you could achieve this yourself. Also, I think there are probably better ways of doing this.

answered Sep 14, 2011 at 13:01

Schroedingers Cat

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2 Comments

musefan Over a year ago

doesnt compile, and if it did you could hit an index out of bounds error with the wrong search string

Schroedingers Cat Over a year ago

it is only rough. And it will sort of work. It was the quickest way of typing it. It should point towards the right solution.

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