Programming help

Hi,

This is my first time posting to a 4Chan text board so i apologize if i seem a bit selfish asking for help in my first post but this is the only board that im confident has frequent users.

Here is my question:
For a homework assignment in C/C++ i need to have some code that will terminate the program if the user inputs a value outside of a preset range. Ive looked through the book and all the class notes i have and cant seem to find any reference on how to make that happen. I know someone here should be able to give me an idea on how to do this.

<input type="button" value="butan" onclick="a=alert;alert=new Function('a(42)')"><br>
<input value="1" id="num0"><input value="0" id="num1">
<input type="button" value="divide" onclick="alert(document.getElementById('num0').value/document.getElementById('num1').value)">