1. Exception Handling
CSCI293 - C#
October 3, 2005

2. Definition
An exception is an event that occurs during the execution of a program that disrupts the normal flow of instructions during the execution of a program.

3. How Exceptions are Processed
Suppose that main calls function A which calls
function B:
If a statement in B causes an exception and that statement is not inside a try block, then function B throws the exception up to function A.
If A does not handle the exception, then the exception is thrown up to main.
If main throws an exception, the program crashes.

4. static void Main(string[] args){
Console.WriteLine("inside main");
func1();
Console.WriteLine("leaving main"); }
static void func1()
Console.WriteLine("inside func1");
func2();
Console.WriteLine("leaving func1");
static void func2()
Console.WriteLine("inside func2");
int a = 0, b=9, c;
c = b/a;
Console.WriteLine("leaving func2");

5. Try Statement try catch { code that may have a problem }
"Do, or do not.
There is no 'try'".
-- Yoda
try {
code that may have a problem }
catch
what to do if error occurs

6. static void Main(string[] args){
Console.WriteLine("inside main");
func1();
Console.WriteLine("leaving main"); }
static void func1()
Console.WriteLine("inside func1");
try
func2();
catch
Console.WriteLine("func1 caught an execption");
Console.WriteLine("leaving func1");
static void func2()
Console.WriteLine("inside func2");
int a = 0, b=9, c;
c = b/a;
Console.WriteLine("leaving func2");

7. If at first you don’t succeed, try, try again...{
func2(); }
catch (System.ArithmeticException e)
Console.WriteLine("func1 - " + e.Message);
catch
Console.WriteLine("func1 - unknown exception

8. Create your own... Exceptions are objects, like everything else:
public class MyException :
System.ApplicationException {
public MyException (string msg)
base (msg) }

9. Intentionally Causing Problems
Assuming errorHasOccurred is one of our variables...
if (errorHasOccurred)
throw new MyException();

10. int[] list = new int[10];
string inputline;
int intvalue = 0;
Console.WriteLine("Enter ten integers");
for (int i=0; i<10; i++) {
inputline = Console.ReadLine();
try
intvalue = Convert.ToInt32(inputline); }
catch { }
list[i] = intvalue;
Console.WriteLine("bob contains: ");
foreach (int x in list)
Console.Write("{0} ", x);
Console.WriteLine();

11. int[] list = new int[10];
string inputline;
int intvalue = 0;
Console.WriteLine("Enter ten integers");
for (int i=0; i<10; i++)
try {
inputline = Console.ReadLine();
intvalue = Convert.ToInt32(inputline);
list[i] = intvalue; }
catch { }
Console.WriteLine("bob contains: ");
foreach (int x in list)
Console.Write("{0} ", x);
Console.WriteLine();