generate random string with pattern in C#

You could give this a shot.

 var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789@#$%^&*(){}[]|?";
 var CharsA = new char[15];
var random = new Random();
 for (int i = 0; i < CharsA.Length; i++)
  {
 CharsA[i] = chars[random.Next(chars.Length)];
  }
 var final = new String(CharsA);

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Or like this.

            var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
            var chars1 = "0123456789";
            var chars2 = "@#$%^&*(){}[]|?";
            var CharsA = new char[15];
            var random = new Random();
            for (int i = 0; i < CharsA.Length; i++)
            {
                if (i <= 12)
                {
                    CharsA[i] = chars[random.Next(chars.Length)];
                }
                if (i == 13)
                {
                    CharsA[i] = chars1[random.Next(chars1.Length)];
                }
                if (i == 14)
                {
                    CharsA[i] = chars2[random.Next(chars2.Length)];
                }
            }
            var final = new String(CharsA);

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MAX LENGTH - 15
NUMERIC- 1
LOWER CASE - 1
UPPER CASE - 1
NON-APLHA NUMERIC - 1

Do you mean the 15 character string must have at least 1 of Numeric ,Upper Case, Lower Case, Non-Alpha Numeric. Or a string of up to 15 Characters meeting the above rules

Thanks All for posting different solutions. I will try and update which works well.

Mr David, yes (15 character string must have at least 1 of Numeric ,Upper Case, Lower Case, Non-Alpha Numeric).

Thanks everyone for your help