Display unique characters only in a textbox

Question

If I give the input from Text Box like

AaBbcdCDEb

the output should be

ABCDE or abcde

only unique characters should be there, no repeated characters.

How do I do this?

Answer 1

Use the Distinct extention method on the array of characters then recombine them into a string.

new string("AaBbcdCDEb".ToLower().Distinct().ToArray());

Answer 2

foreach char in textbox, if textbox/new string contains char then return, else add to new string?

Answer 3

string input = "AABBCCDD";
string output = string.empty; 
foreach(char c in input)
    if (!output.Contains(c))
        output += c;