switch matter fallthrough c#?

switch matter fallthrough personal vital reasons regretful switch vs. if/else if constructs. an instance method here:

static twine numbertowords(int number)
{
    string[] numbers = new string[] 
        { "", "one", "two", "three", "four", "five", 
          "six", "seven", "eight", "nine" };
    string[] tens = new string[] 
        { "", "", "twenty", "thirty", "forty", "fifty", 
          "sixty", "seventy", "eighty", "ninety" };
    string[] teenagers = new string[]
        { "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen",
          "sixteen", "seventeen", "eighteen", "nineteen" };

    twine ans = "";
    switch (number.tostring().length)
    {
        box 3:
            ans += string.format("{0} hundred ", numbers[number / 100]);
        box 2:
            int t = (number / 10) % 10;
            (t == 1)
            {
                ans += teens[number % 10];
                break;
            }
            else (t > 1)
                ans += string.format("{0}-", tens[t]);
        box 1:
            int o = array % 10;
            ans += numbers[o];

            break;
        default:
            pitch new argumentexception("number");
    }
    relapse ans;
}

the intelligent deferential since string[]s should announced outmost function: well, are, only an example.

the compiler fails following error:

control can't tumble by box tag ('case 3:') another
control can't tumble by box tag ('case 2:') another

why? there any proceed arrange intrepidity but carrying 3 ifs?