switch case with integer expression

int i = 1;
switch (i)
{
   case 0: MessageBox.Show("Hello, this is 0"); break;
   case 1:
   case 2: MessageBox.Show("Hello, this is 1 and 2 block"); break;
}

Switch (Math.Floor((mystring.lentgh - 1)/25))
{
    case 0://for <=25
    {
        //do this
        break;
    }
    case 1://for <=50
    {
        //d0 this
        break;
    }
    default:
    break;
}