C# program to determine if a string has all unique characters

Use the substring() method in C# to check each and every substring for unique characters. Loop it until the length of the string.

If any one the substring matches another, then it would mean that the string do not have unique characters.

You can try to run the following code to determine if a string has all unique characters.


 Live Demo

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
public class Demo {
   public bool CheckUnique(string str) {
      string one = "";
      string two = "";
      for (int i = 0; i < str.Length; i++) {
         one = str.Substring(i, 1);
         for (int j = 0; j < str.Length; j++) {
            two = str.Substring(j, 1);
            if ((one == two) && (i != j))
            return false;
      return true;
   static void Main(string[] args) {
      Demo d = new Demo();
      bool b = d.CheckUnique("amit");