var A = "abc".ToCharArray();
var B = "12".ToCharArray();
var C = "jklm".ToCharArray();

var count = 0;
foreach(var a in A)
    foreach (var b in B)
        foreach (var c in C)
        {
            Console.WriteLine(a + "|" + b + "|" + c);
            count++;
        }

Console.WriteLine(count);

var arrays = new List<char[]>() { A, B, C};