I'm not totally sure what you are trying to do, but if you are trying to show a message for a range of values,
70+ Distinction
69...60 Average
59 and below Failed
Then a Switch is not the best way to do it: it only matches exact values, rather than a range. You woudl either have to list each value in the switch:
switch (mark)
{
case 100:
case 99:
case 98:
case 97:
...
case 72:
case 71:
case 70:
Console.WriteLine(" you are distinction");
Console.ReadLine();
break;
Which is very clumsy, and difficult to read.
You could use a switch, if you used a division:
switch ((int) mark / 10)
{
case 10:
case 9:
case 8:
case 7:
Console.WriteLine(" you are distinction");
Console.ReadLine();
break;
case 6:
Console.WriteLine(" Average");
Console.ReadLine();
break;
...
But even then it is difficult to maintain - what if necxt year the Average mark is changed to 65?
You would be much better using an if...else construct:
if (mark >= 70) Console.WriteLine(" you are distinction");
else if (mark >= 60) Console.WriteLine(" Average");
else Console.WriteLine(" Failed");
Console.Readline();
It's a lot clearer to read, and you can replace the "magic numbers" with readable constant, or file driven values.