Question

I have a textbox where the user enters a random string. I want to count the number of vowels(A,E,I,O,U) in the string and show th results in the labelcontrol.

protected void Button1_Click(object sender, EventArgs e)
    {
        string EnterString;
        EnterString = TextBox1.Text;
        char ch1 = 'a';
        char ch2 = 'e';
        char ch3 = 'i';
        char ch4 = 'o';
        char ch5 = 'u';

        int counta = 0;
        int counte = 0;
        int counti = 0;
        int counto = 0;
        int countu = 0;
        char ch6 = 'A';
        char ch7 = 'E';
        char ch8 = 'I';
        char ch9 = 'O';
        char ch10 = 'U';

        int countA = 0;
        int countE = 0;
        int countI = 0;
        int countO = 0;
        int countU = 0;

        //const string vowels = "aeiou";
        /* return value.Count(chr => vowels.Contains(char.ToLower(chr)));
         return Value.Count()*/
        int j = counta + counte + counti + counto + countu + countA + countE + countI + countO + countU;

        foreach (char v in EnterString)
        {
            if (v == ch1) { counta++; j++; }

            else if (v == ch2) { counte++; j++; }

            else if (v == ch3) { counti++; j++; }

            else if (v == ch4) { counto++; j++; }

            else if (v == ch5) { countu++; j++; }
        }
        foreach (char v in EnterString)
        {
            if (v == ch6) { countA++; j++; }

            else if (v == ch7) { countE++; j++; }

            else if (v == ch8) { countI++; j++; }

            else if (v == ch9) { countO++; j++; }

            else if (v == ch10) { countU++; j++; }
        }

        Label1.Text = j.ToString();
    }

Answer 1

You have this in your code:

const string vowels = "aeiou";
return value.Count(chr => vowels.Contains(char.ToLower(chr)));

That works, at least if your culture is US. So no idea why you commented it out in favor of the current monstrosity.

On a Turkish locale it will fail because the lower case of I is not i but ı (undotted). So if you define vowels as aeiouAEIOU you should use ToLowerInvariant.

But if you want to include other vowels (like Ä) I have no idea how to do that except by listing all the characters.

Full implementation:

int CountVowels(string value)
{
    const string vowels = "aeiou";
    return value.Count(chr => vowels.Contains(char.ToLowerInvariant(chr)));
}

Looks like you got the good code part from:
Counting vowels using switch