C# Exception Handling

Sinu Joseph

create a reference type called person.Populate the person class with the following properties to store the following info:

firstname,lastname,email address, date of birth

Add constructor that accept the following [parameter list:

all four parameters (first,last,email,dateofbirth)

Add readonly property that return the following computed information

Adult - whether or not the person is over 18

birthday - whether or not today is the person birthday

handle the following execptions

date of birth is in the future

date of birth is too far in the past(we're only dealing with who are alive)

invalid email address

CAN ANYBODY HELP ME OUT TO SOLVE THESE

PLZ..

26 Replies

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Vulpes13y ago
Accepted answer
Oops, I've inadvertently by-passed the error handling code by setting the fields directly rather than via the properties!

Sorry about that which I've now corrected.

If you want to catch the exceptions as well, then this will need to be done in the constructor, otherwise the person object won't be created.

Notice that if the email address is invalid, it remains at null.

If the date of birth is invalid, it remains at its default value of 01/01/0001:

using System;

class person // all classes are reference types
{
// private backing fields for properties
string _firstname;
string _lastname;
string _email;
DateTime _dateofbirth;

public string firstname
{
get { return _firstname; }
set { _firstname = value; }
}

public string lastname
{
get { return _lastname; }
set { _lastname = value; }
}

public string email
{
get { return _email; }
set
{
// make sure there's just one @ in it:
string[] items = value.Split('@'); // split the string using @ as a separator
if (items.Length != 2) // there should be exactly 2 items if it's valid
{
throw new ArgumentException("Invalid email address");
}
_email = value; // otherwise it's OK to set it
}
}

public DateTime dateofbirth
{
get { return _dateofbirth; }
set
{
if (value > DateTime.Today) // if it's after today
{
throw new ArgumentException("Date of birth can't be in the future");
}
_dateofbirth = value; // otherwise it's OK to set it
}
}

public person(string first, string last, string email, DateTime dateofbirth)
{
this.firstname = first;
this.lastname = last;

try
{
this.email = email;
}
catch(Exception ex)
{
Console.WriteLine();
Console.WriteLine(ex.Message);
}

try
{
this.dateofbirth = dateofbirth;
}
catch(ArgumentException ex)
{
Console.WriteLine();
Console.WriteLine(ex.Message);
}
}

public bool Adult // readonly property has only a 'get'
{
get
{
DateTime eighteen = _dateofbirth.AddYears(18); // 18th birthday
if (DateTime.Today >= eighteen) return true; // adult if 18 or over
return false; // otherwise minor
}
}

public bool birthday
{
get
{
DateTime today = DateTime.Today;
if (today.Month == _dateofbirth.Month && today.Day == _dateofbirth.Day)
{
return true;
}
return false;
}
}
}

// add this to make sure the class compiles OK
class Test
{
static void Main()
{
Console.WriteLine("Enter details for a person\n");
Console.Write(" First name : ");
string first = Console.ReadLine();
Console.Write(" Last name : ");
string last = Console.ReadLine();
Console.Write(" Email address : ");
string email = Console.ReadLine();
Console.Write(" Date of birth : ");
string dob = Console.ReadLine();
DateTime dateofbirth = DateTime.Parse(dob);
person p = new person(first, last, email, dateofbirth);
Console.WriteLine();
Console.WriteLine("The person entered is : {0} {1}", p.firstname, p.lastname);
Console.WriteLine("Email address is: {0}", p.email);
Console.WriteLine("Date of birth is: {0}", p.dateofbirth.ToShortDateString());
Console.WriteLine("Adult : {0}", p.Adult);
Console.WriteLine("Birthday today : {0}", p.birthday);
Console.ReadKey();
}
}

Some sample output, throwing both exceptions:

Enter details for a person

First name : John
Last name : Smith
Email address : john@[email protected]
Date of birth : 01/01/2014

Invalid email address

Date of birth can't be in the future

The person entered is : John Smith
Email address is:
Date of birth is: 01/01/0001
Adult : True
Birthday today : False
Sinu Joseph13y ago
i have a form in that i 3 texxtboxes named Rollno,name,ageand course
and i have 2 class 1 for connection named MyDBConeection and 1 is for all data related class called student
in MyDbConnection I gave connection details
in my student class i gave 4 properties named Rollno,Name,Age,Course and corresponding methods

public int Getdetails
{
it will display all details in grid view
}

public dataset update ()
{
update the table
}

BUT i need is this

i have a button in my form called getdetails before update
like this

roll no - textbox
then getdetails button

then name,age and course then update button

i want to display all details in my textbox while clicking on the getdetails button then update

plzz help...............
Sinu Joseph13y ago
can u help me to ans this
i have a form ...
in that i have 4 textbox called customerid,name and address,phone no
but customerid entered starts with letter'C' and has three digits after it,
and the phone no value should be integer ..
how can u do it ..plz help ...me
Sinu Joseph13y ago
sorry vulpes i changed my name to sisanurah
because my mam will saw me .. thts y ...
dnt forget to answer my questions
Vulpes13y ago
The reason for that error is because the user isn't entering a valid date in the first place.

However, you can force the use to enter a valid date before it's tested for being too late or too early as follows:

static void Main()
{
Console.WriteLine("Enter details for a person\n");
Console.Write(" First name : ");
string first = Console.ReadLine();
Console.Write(" Last name : ");
string last = Console.ReadLine();
Console.Write(" Email address : ");
string email = Console.ReadLine();
DateTime dateofbirth;
bool isValid;

do
{
Console.Write(" Date of birth : ");
string dob = Console.ReadLine();
isValid = DateTime.TryParse(dob, out dateofbirth);
if(!isValid) Console.WriteLine(" Not a valid date, try again");
}
while(!isValid);

person p = new person(first, last, email, dateofbirth);
Console.WriteLine();
Console.WriteLine("The person entered is : {0} {1}", p.firstname, p.lastname);
Console.WriteLine("Email address is: {0}", p.email);
Console.WriteLine("Date of birth is: {0}", p.dateofbirth.ToShortDateString());
Console.WriteLine("Adult : {0}", p.Adult);
Console.WriteLine("Birthday today : {0}", p.birthday);
Console.ReadKey();
}

The DateTime.TryParse tests whether a string represents a valid date or not. If it does, it returns true otherwise it returns false. If it is valid, the 'out' parameter will contain that date otherwise it contains the default date (01/01/0001).

The code keeps looping ('do' statement) until a valid date is entered.
Sinu Joseph13y ago
everthg is working but the date of birth is not handled
i uploaded the screen shot
if we leave dateofbirth column it will terminate the program and point out the error in our prgm

" Console.Write(" Date of birth : "); string dob = Console.ReadLine();
DateTime dateofbirth = DateTime.Parse(dob);----> error (String was not recognized as a valid DateTime. )
person p = new person(first, last, email, dateofbirth); "
Vulpes13y ago
We are in fact using constructor overloading here. However, to save having to repeat all the code again, we're also using constructor chaining (: this() syntax) which is a common technique in these circumstances.

If you haven't yet learned about constructor chaining, then you will have to repeat the code again.

The two constructors which take 3 parameters will then become:

public person(string first, string last, string email)
{
this.firstname = first;
this.lastname = last;

try
{
this.email = email;
}
catch(Exception ex)
{
Console.WriteLine();
Console.WriteLine(ex.Message);
this.email = "@"; // use this as default, say
}

this.dateofbirth = DateTime.Today; // use this as default, say
}

public person(string first, string last, DateTime dateofbirth)
{
this.firstname = first;
this.lastname = last;
this.email = "@"; // use this as default, say

try
{
this.dateofbirth = dateofbirth;
}
catch(ArgumentException ex)
{
Console.WriteLine();
Console.WriteLine(ex.Message);
this.dateofbirth = DateTime.Today; // use this as default, say
}
}
Sinu Joseph13y ago
is it constructor overloading

mam asked me do with constuctor overloading..

if the user enters first,last and email then constructor with 3 parameter will invoked and the 4 th value will be nill

sorry,,,
Vulpes13y ago
OK, to avoid repeating code, we can use 'constructor chaining' for the constructors which take 3 parameters to chain to the one which takes 4 parameters with a suitable default value for the 'missing' parameter.

One other thing I missed before is that we have to make sure that the date of birth is such that we're only dealing with living people. Now the oldest ever (documented) person was 122 so we will throw an exception if some-one would be 123 or more.

Here's the revised code - with the changes highlighted. I'll leave it to you to come up with code to test the new constructors if you feel it's necessary:

using System;

class person // all classes are reference types
{
// private backing fields for properties
string _firstname;
string _lastname;
string _email;
DateTime _dateofbirth;

public string firstname
{
get { return _firstname; }
set { _firstname = value; }
}

public string lastname
{
get { return _lastname; }
set { _lastname = value; }
}

public string email
{
get { return _email; }
set
{
// make sure there's just one @ in it:
string[] items = value.Split('@'); // split the string using @ as a separator
if (items.Length != 2) // there should be exactly 2 items if it's valid
{
throw new ArgumentException("Invalid email address");
}
_email = value; // otherwise it's OK to set it
}
}

public DateTime dateofbirth
{
get { return _dateofbirth; }
set
{
if (value > DateTime.Today) // if it's after today
{
throw new ArgumentException("Date of birth can't be in the future");
}
else if (value <= DateTime.Today.AddYears(-123))
{
throw new ArgumentException("Age can't be more than 122");
}
_dateofbirth = value; // otherwise it's OK to set it
}
}

public person(string first, string last, string email, DateTime dateofbirth)
{
this.firstname = first;
this.lastname = last;

try
{
this.email = email;
}
catch(Exception ex)
{
Console.WriteLine();
Console.WriteLine(ex.Message);
this.email = "@"; // use this as default, say
}

try
{
this.dateofbirth = dateofbirth;
}
catch(ArgumentException ex)
{
Console.WriteLine();
Console.WriteLine(ex.Message);
this.dateofbirth = DateTime.Today; // use this as default, say
}
}

// chain to constructor which has 4 parameters
public person(string first, string last, string email) : this(first, last, email, DateTime.Today)
{
}

// chain to constructor which has 4 parameters
public person(string first, string last, DateTime dateofbirth) : this(first, last, "@", dateofbirth)
{
}

public bool Adult // readonly property has only a 'get'
{
get
{
DateTime eighteen = _dateofbirth.AddYears(18); // 18th birthday
if (DateTime.Today >= eighteen) return true; // adult if 18 or over
return false; // otherwise minor
}
}

public bool birthday
{
get
{
DateTime today = DateTime.Today;
if (today.Month == _dateofbirth.Month && today.Day == _dateofbirth.Day)
{
return true;
}
return false;
}
}
}

// add this to make sure the class compiles OK
class Test
{
static void Main()
{
Console.WriteLine("Enter details for a person\n");
Console.Write(" First name : ");
string first = Console.ReadLine();
Console.Write(" Last name : ");
string last = Console.ReadLine();
Console.Write(" Email address : ");
string email = Console.ReadLine();
Console.Write(" Date of birth : ");
string dob = Console.ReadLine();
DateTime dateofbirth = DateTime.Parse(dob);
person p = new person(first, last, email, dateofbirth);
Console.WriteLine();
Console.WriteLine("The person entered is : {0} {1}", p.firstname, p.lastname);
Console.WriteLine("Email address is: {0}", p.email);
Console.WriteLine("Date of birth is: {0}", p.dateofbirth.ToShortDateString());
Console.WriteLine("Adult : {0}", p.Adult);
Console.WriteLine("Birthday today : {0}", p.birthday);
Console.ReadKey();
}
}

Some sample output, throwing both exceptions:

Enter details for a person

First name : John
Last name : Smith
Email address :
Date of birth : 31/05/1890

Invalid email address

Age can't be more than 122

The person entered is : John Smith
Email address is: @
Date of birth is: 31/05/2013
Adult : False
Birthday today : True
Sinu Joseph13y ago
Add constructor that accept the following [parameter list:

all four parameters ,
person( first,last,email)
person (first,last,dateofbirth)

constructoe with 4 opara
with 3para
and with 2 para

canu do it for me ...

add code for this too..
Vulpes13y ago
I'd say it was doing that already.

If you look back at the code where we entered John Smith with some deliberately invalid data:

Email address : john@[email protected] (too many @'s)
Date of birth : 01/01/2014 (in the future)

The constructor then printed the following messages:

Invalid email address

Date of birth can't be in the future

I don't think it's saying that you should print a message if the data is valid as that would be pointless.
Sinu Joseph13y ago
hi vulpes,

hey can u help ..
mam gave me some modification for tht question

create a reference type called person.Populate the person class with the following properties to store the following info:

firstname,lastname,email address, date of birth

Add constructor that accept the following [parameter list:
use constructor overload
all four parameters (first,last,email,dateofbirth),
with first,last,email
with first,last,dateofbirth

and must show msg after entering date or email..
eg if we entered wrong email then show msg after entering email
or date

Add readonly property that return the following computed information

Adult - whether or not the person is over 18
birthday - whether or not today is the person birthday

handle the following execptions

date of birth is in the future
date of birth is too far in the past(we're only dealing with who are alive)
invalid email address

CAN ANYBODY HELP ME OUT TO SOLVE THESE
PLZ..
Vulpes13y ago
I'm not angry at all as I want people to be able to understand my posts.

So, if you have any more queries, don't be afraid to ask :)
Sinu Joseph13y ago
THANK U VULPES

sorry 4 disturbing u a lot...
i thk u r soo angry because of me rt..
sorry :(

i just wanna study thats all ..
anyway u have good knowldge in c#..

thanks 4 helping me
Vulpes13y ago
Well, there are a number of points here.

The first one - I think fairly obvious - is that a readonly property can only have a 'get'. If it had a 'set' as well, then it wouldn't be read only.

Within the body of the 'get', we first have to find the person's 18th birthday by adding 18 years to his/her birthday. There's a built in DateTime method (AddYears) which does this for us.

We then check to see whether today is on or after the 18th birthday. We can use the >= operator for this, just like we do for numbers.

If it is, then the person's an adult and we return true.

Otherwise, the person's a minor and we return false.
Sinu Joseph13y ago
hello vulpes
sorry 4 disturbing u agian

can u explain this also plz...

public bool Adult // readonly property has only a 'get'
{
get
{
DateTime eighteen = _dateofbirth.AddYears(18); // 18th birthday
if (DateTime.Today >= eighteen)
{
return true;
}// adult if 18 or over
return false; // otherwise minor
}
}
Sinu Joseph13y ago
hello vulpes

Thank u soo much i understood everythg...
Vulpes13y ago
All property 'setters' in C# have an implicit variable called 'value' which represents the value to which the property is set.

So in this line:

p.firstname = "sinu";

'value' will be equal to "sinu".

Properties are really methods under the hood and the firstname property would be converted to something like this by the compiler:

public string get_firstname()
{
return _firstname;
}

public void set_firstname(string value)
{
_firstname = value;
}

This shows more clearly where 'value' is coming from.
Sinu Joseph13y ago
public string firstname
{
get { return _firstname; }
set { _firstname = value; }---> can u explain this value .. y u r given purpose .. plz..
}

public string lastname
{
get { return _lastname; }
set { _lastname = value; }
}

public string email
{
get { return _email; }
set
{
// make sure there's just one @ in it:
string[] items = value.Split('@'); // split the string using @ as a separator
if (items.Length != 2) // there should be exactly 2 items if it's valid
{
throw new ArgumentException("Invalid email address");
}
_email = value; // otherwise it's OK to set it
}
}

public DateTime dateofbirth
{
get { return _dateofbirth; }
set
{
if (value > DateTime.Today) // if it's after today
{
throw new ArgumentException("Date of birth can't be in the future");
}
_dateofbirth = value; // otherwise it's OK to set it
}
}
Sinu Joseph13y ago
hi vulpes
but here if we entered wrong date there is no msg shown.

we have to handle the exception ..
if the email is not correct show a msg invalid email.
can u do that for me please
handle the following execptions

date of birth is in the future
date of birth is too far in the past(we're only dealing with who are alive)
invalid email address
Sinu Joseph13y ago
handle the following execptions

date of birth is in the future
date of birth is too far in the past(we're only dealing with who are alive)
invalid email address
Sinu Joseph13y ago
but the execptions are not handled na ..
msg hav to print...
Vulpes13y ago
Sure, here we are:

// add this to make sure the class compiles OK
class Test
{
static void Main()
{
Console.WriteLine("Enter details for a person\n");
Console.Write(" First name : ");
string first = Console.ReadLine();
Console.Write(" Last name : ");
string last = Console.ReadLine();
Console.Write(" Email address : ");
string email = Console.ReadLine();
Console.Write(" Date of birth : ");
string dob = Console.ReadLine();
DateTime dateofbirth = DateTime.Parse(dob);
person p = new person(first, last, email, dateofbirth);
Console.WriteLine();
Console.WriteLine("The person entered is : {0} {1}", p.firstname, p.lastname);
Console.WriteLine("Email address is: {0}", p.email);
Console.WriteLine("Date of birth is: {0}", p.dateofbirth.ToShortDateString());
Console.WriteLine("Adult : {0}", p.Adult);
Console.WriteLine("Birthday today ; {0}", p.birthday);
Console.ReadKey();
}

If we run the program and enter Barack's details again, the console output will be:

Enter details for a person

First name : Barack
Last name : Obama
Email address : [email protected]
Date of birth : 4/8/1961

The person entered is : Barack Obama
Email address is: [email protected]
Date of birth is: 04/08/1961
Adult : True
Birthday today ; False
Sinu Joseph13y ago
hi vipes
its not working yar can u provide the working
i need is tht the user can enter the value at runtime
Sinu Joseph13y ago
hello vipes
thanks for the answer ...
is it possible tht the user can enter the values .for ths question
Vulpes13y ago
The following should cover those requirements:

using System;

class person // all classes are reference types
{
// private backing fields for properties
string _firstname;
string _lastname;
string _email;
DateTime _dateofbirth;

public string firstname
{
get { return _firstname; }
set { _firstname = value; }
}

public string lastname
{
get { return _lastname; }
set { _lastname = value; }
}

public string email
{
get { return _email; }
set
{
// make sure there's just one @ in it:
string[] items = value.Split('@'); // split the string using @ as a separator
if (items.Length != 2) // there should be exactly 2 items if it's valid
{
throw new ArgumentException("Invalid email address");
}
_email = value; // otherwise it's OK to set it
}
}

public DateTime dateofbirth
{
get { return _dateofbirth; }
set
{
if (value > DateTime.Today) // if it's after today
{
throw new ArgumentException("Date of birth can't be in the future");
}
_dateofbirth = value; // otherwise it's OK to set it
}
}

public person(string first, string last, string email, DateTime dateofbirth)
{
_firstname = first;
_lastname = last;
_email = email;
_dateofbirth = dateofbirth;
}

public bool Adult // readonly property has only a 'get'
{
get
{
DateTime eighteen = _dateofbirth.AddYears(18); // 18th birthday
if (DateTime.Today >= eighteen) return true; // adult if 18 or over
return false; // otherwise minor
}
}

public bool birthday
{
get
{
DateTime today = DateTime.Today;
// if today's month and day are same as date of birth's, it's a birthday
if (today.Month == _dateofbirth.Month && today.Day == _dateofbirth.Day)
{
return true;
}
return false;
}
}
}

// add this to make sure the class compiles OK
class Test
{
static void Main()
{
person p = new person("Barack", "Obama", "[email protected]", new DateTime(1961, 8, 4));
}
}