如何在数组中查找多个值？

Question

My code below looks only for one letter, how can I look for combination of letters? For ex.: to find letters "ac" in my array and to output them to textBox2

string[] alphabet = new string[] { "a", "b", "c"};
for (int letter = 0; letter < alphabet.Length; letter++)
{
    if (textBox1.Text == alphabet[letter])
    textBox2.Text = alphabet[letter];
}

Answer 1

I guess you want to check if only letters of the array are entered in the textbox:

bool valid = textBox1.Text.All(c => alphabet.Contains(c.ToString()));

if it was a char[] you could write:

bool valid = textBox1.Text.All(alphabet.Contains);

Then you could also use Enumerable.Except to get the set difference:

var notValidLetters = textBox1.Text.Except(alphabet);
textBox2.Text = "Following are not valid letters: " + String.Join(", ", notValidLetters);

Answer 2

Considering your problem is "Find both a and c from the given string ac ";

string[] alphabet = new string[] { "a", "b", "c"};
        for (int letter = 0; letter < alphabet.Length; letter++)
        {
            if (textBox1.Text.Any(alphabet[letter]))
                textBox2.Text += alphabet[letter];
        }