Switch Statement Problem

Using switch statement, how can i create a program that ask the user to enter choices 1,2 or 3 only and do the problem below?
SAMPLE OUTPUT

*********CHOICES*********
[1] number to roman
[2] 12hour to 24hour clock
[3] exit
*************************
ENTER YOUR CHOICE:4
INVALID.
(Terminated)

ENTER YOUR CHOICE:1

[1] Conversion
Create a program that prompts the user to enter a number (from 1-3000 only) then output the number and its corresponding roman numeral number.

[2] 12Hr clock  24Hr clock
Create a program that will prompt the user to input time based on a 12-hour clock and output the corresponding time based on a 24-hour clock. Check all possible invalid input data.

 

Code:

printf("[display menu]");
char buf[32];
fgets(buf,30,stdin);
switch (atoi(buf))
{
case 1: /* do the 1 stuff */ break;
case 2: /* do the 2 stuff */ break;
case 3: /* do the 3 stuff */ break;
default: printf("INVALID\n"); break;
}