quantum-space-buddies/EpicOnlineTransport/RandomString.cs

using System;
using System.Text;

public class RandomString {

    // Generates a random string with a given size.    
    public static string Generate(int size) {
        var builder = new StringBuilder(size);

        Random random = new Random();

        // Unicode/ASCII Letters are divided into two blocks
        // (Letters 65–90 / 97–122):
        // The first group containing the uppercase letters and
        // the second group containing the lowercase.  

        // char is a single Unicode character  
        char offsetLowerCase = 'a';
        char offsetUpperCase = 'A';
        const int lettersOffset = 26; // A...Z or a..z: length=26  
        
        for (var i = 0; i < size; i++) {
            char offset;
            if(random.Next(0,2) == 0) {
                offset = offsetLowerCase;
            } else {
                offset = offsetUpperCase;
            }

            var @char = (char) random.Next(offset, offset + lettersOffset);
            builder.Append(@char);
        }

        return builder.ToString();
    }
}