Checking if string exists in List C#

Question

I've been coding a program that stores student data (name and age) in a .txt file. I am now doing the delete method. However, when the user enters a string, I want it to compare the input to the strings in my List<string>, that's full of names. Code:

    string tempFileName;
    string inputSel; // Selection string for delete
    Console.WriteLine(" -- Deleting Grade {0} -- ", grade);
    Console.WriteLine("- Enter a student name to delete: ");
    foreach (string file in fileNames)
    {
        tempFileName = file.Replace(".txt", "");
        studentNames.Add(tempFileName);
    }
    foreach (string name in studentNames)
    {
        Console.Write("{0}\n", name);
    }
    Console.WriteLine();
    Console.Write("> ");
    inputSel = Console.ReadLine();
    string input = inputSel.ToLower();
    string tempString;
    bool foundString = false;
    foreach (string file in studentNames)
    {
        tempString = file.ToLower();
        if (inputSel == tempString)
        {
            foundString = true;
        }
    }
    if (!foundString)
    {
        Console.WriteLine("Wrong name entered!");
        Console.WriteLine("Returning to grades menu..");
        Console.WriteLine("Press any key to continue.");
        Console.ReadKey();
        return;
    }

As you can see, the program stores inputSel into input (ToLower()), then compares each string in studentNames List<string>, and if it finds a match it flips the foundString bool, but even if I enter a name that matches (for example, it says JacobMusterson, I enter JacobMusterson, it should skip the "student not found", but it doesn't.

Kamil Budziewski · Accepted Answer · 2013-10-30 07:53:14Z

2

you should use input not inputSel

if (input == tempString)
{
    foundString = true;
}

because of line:

string input = inputSel.ToLower();

where you are assinging to input lower version of inputSel

I suggest you to use IngonreCase in string.Compare for not making ToLower()

var b =  string.Compare("a","A",StringComparison.OrdinalIgnoreCase);

it will return 0 if equal see here

EDIT:

personally I would use:

var exists = studentNames.Any(x=>string.Compare(x,inputSel,StringComparison.OrdinalIgnoreCase)==0);

edited Oct 30, 2013 at 7:53

answered Oct 30, 2013 at 7:47

Kamil Budziewski

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2 Comments

Ilan Over a year ago

Wow, I can't believe I missed that. Thanks a lot! (Why can't I accept answers?)

Kamil Budziewski Over a year ago

@Ilan321 you can, but you have to wait several minutes, popup says that

Marco Forberg · Accepted Answer · 2013-10-30 08:11:17Z

1

you can simply do it this way:

Boolean foundString = studentNames.Exists(name => name.ToLower().Equals(input));

edited Oct 30, 2013 at 8:11

answered Oct 30, 2013 at 7:57

Marco Forberg

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Comments

jeet chheda · Accepted Answer · 2021-05-20 06:46:54Z

1

Why not simply use,

if(list.Contains(s)){
    //found
}else{
    //not found
}

Where list is List<String> and s is a String

answered May 20, 2021 at 6:46

jeet chheda

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Comments

Kirill Bestemyanov · Accepted Answer · 2013-10-30 07:53:09Z

It will be more readable and effective if you will use Contains method of List:

foreach (string file in studentNames)
    {
        tempString = file.ToLower();
        if (inputSel == tempString)
        {
            foundString = true;
        }
    }
if (!foundString)
    {
        Console.WriteLine("Wrong name entered!");
        Console.WriteLine("Returning to grades menu..");
        Console.WriteLine("Press any key to continue.");
        Console.ReadKey();
        return;
    }

can be rewrite:

if(!studentNames.Contains(inputSel, StringComparer.Create(CultureInfo.InvariantCulture, true)))
{
            Console.WriteLine("Wrong name entered!");
            Console.WriteLine("Returning to grades menu..");
            Console.WriteLine("Press any key to continue.");
            Console.ReadKey();
            return;
}

Tomtom · Accepted Answer · 2013-10-30 07:54:14Z

0

Just a small comment on your foreach-loop. You always iterating through all entries in the loop also if you already found out that the string is in the collection.

You can improve the performance of your code by replacing the last foreach.

Try:

bool foundString = studentNames.Select(file => file.ToLower()).Any(tempString => inputSel == tempString);

answered Oct 30, 2013 at 7:54

Tomtom

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