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028_method_parameters/028_csharp.md
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---
##
## Exercise
### Methods with optional parameters
The C Sharp language allows the use of named and optional parameters. These
types of parameters let you select which arguments you want to supply to the
method, so you aren't restricted to the structure defined in the method
signature.
Named arguments allow you to specify the value for a parameter using its name
rather than position. Optional parameters allow you to omit those arguments
when calling the method.
In this exercise, you'll learn how to use both named and optional parameters.
#### Create an RSVP application
In this task, you'll create a brief application for guests to RSVP to an event.
The guests will provide their party size and any allergies. You'll also add the
option to restrict RSVPs to an invite-only guest list.
Type the following code into the Visual Studio Code Editor:
```cs
string[] guestList = {"Rebecca", "Nadia", "Noor", "Jonte"};
string[] rsvps = new string[10];
int count = 0;
void RSVP(string name, int partySize, string allergies, bool inviteOnly) {
if (inviteOnly) {
// search guestList before adding rsvp
}
rsvps[count] = $"Name: {name}, \tParty Size: {partySize}, \tAllergies: {allergies}";
count++;
}
void ShowRSVPs() {
Console.WriteLine("\nTotal RSVPs:");
for (int i = 0; i < count; i++){
Console.WriteLine(rsvps[i]);
}
}
```
In this code, you create variables to store the guest list and rsvps. The `RSVP`
method appends guest information to the list, and the `ShowRSVPs` method
displays the total RSVPs using the tab escape sequence to separate guest
information.
Enter the following code in the `RSVP` method to search the guest list:
```cs
if (inviteOnly) {
bool found = false;
foreach (string guest in guestList) {
if (guest.Equals(name)) {
found = true;
break;
}
}
if (!found) {
Console.WriteLine($"Sorry, {name} is not on the guest list");
return;
}
}
```
In this code, you check to see if the given name is equal to any of the names
on the guest list. If a match is found, you set `found` to true and break out
of the `foreach` loop. If `found` is false, you display a message and use the
`return` keyword to terminate the method.
Call your method by adding the following code above the `RSVP` method signature:
```cs
RSVP("Rebecca", 1, "none", true);
RSVP("Nadia", 2, "Nuts", true);
RSVP("Linh", 2, "none", false);
RSVP("Tony", 1, "Jackfruit", true);
RSVP("Noor", 4, "none", false);
RSVP("Jonte", 2, "Stone fruit", false);
ShowRSVPs();
```
Save and run the code to observe the following output:
```txt
Sorry, Tony is not on the guest list
Total RSVPs:
Name: Rebecca, Party Size: 1, Allergies: none
Name: Nadia, Party Size: 2, Allergies: Nuts
Name: Linh, Party Size: 2, Allergies: none
Name: Noor, Party Size: 4, Allergies: none
Name: Jonte, Party Size: 2, Allergies: Stone fruit
```
#### Use named arguments
When calling a method that accepts many parameters, it can be tricky to
understand what the arguments represent. Using named arguments can improve the
readability of your code. Use a named argument by specifying the parameter name
followed by the argument value. In this task, you'll practice using named
arguments.
Locate the following line of code: `RSVP("Linh", 2, "none", false);`
Update the method call as follows:
```cs
RSVP(
name: "Linh",
partySize: 2,
allergies: "none",
inviteOnly: false
);
```
Notice that you supply the name of the parameter, followed by a colon and the
value. This syntax defines a named argument. It isn't necessary to name all of
the arguments. For example, the following syntax is also valid:
- `RSVP("Linh", 2, allergies: "none", inviteOnly: false);`
- `RSVP("Linh", partySize: 2, "none", false);`
Named arguments, when used with positional arguments, are valid if they're used
in the correct position. Named arguments are also valid as long as they're not
followed by any positional arguments. For example, including `"Linh"` and `2` at
the end would be invalid:
`RSVP(allergies: "none", inviteOnly: false, "Linh", 2);`
If you entered this code, you would get the following error:
`Named argument 'allergies' is used out-of-position but is followed by an
unnamed argument`
Locate the following line of code: `RSVP("Tony", 1, "Jackfruit", true);`
Update the method call as follows:
```cs
RSVP(
"Tony",
inviteOnly: true,
allergies: "Jackfruit",
partySize: 1
);
```
Notice that the named arguments don't have to appear in the original order.
However, the unnamed argument `Tony` is a positional argument, and must appear
in the matching position.
Save and run the code to observe the following output:
```txt
Sorry, Tony is not on the guest list
Total RSVPs:
Name: Rebecca, Party Size: 1, Allergies: none
Name: Nadia, Party Size: 2, Allergies: Nuts
Name: Linh, Party Size: 2, Allergies: none
Name: Noor, Party Size: 4, Allergies: none
Name: Jonte, Party Size: 2, Allergies: Stone fruit
```
Notice that using named arguments doesn't change the output.
Declare optional parameters
A parameter becomes optional when it's assigned a default value. If an optional parameter is omitted from the arguments, the default value is used when the method executes. In this step, you'll make the parameters partySize, allergies and inviteOnly optional.
To define optional parameters, update the RSVP method signature as follows:
```cs
void RSVP(
string name,
int partySize = 1,
string allergies = "none",
bool inviteOnly = true
)
```
Take a moment to observe the syntax. The parameters are still separated by
commas, but the parameters `partySize`, `allergies`, and `inviteOnly` are each
assigned to a value.
Next, you'll update the calls to `RSVP` to apply the optional parameters.
Update your code to the following:
```cs
RSVP("Rebecca");
RSVP("Nadia", 2, "Nuts");
RSVP(name: "Linh", partySize: 2, inviteOnly: false);
RSVP("Tony", allergies: "Jackfruit", inviteOnly: true);
RSVP("Noor", 4, inviteOnly: false);
RSVP("Jonte", 2, "Stone fruit", false);
```
In each method call, notice that the name is never omitted. When a method is
called, all required arguments must always be included. However, any optional
arguments can be omitted.
In this code, you removed the arguments `1, "none", true` from Rebecca's rsvp.
Since these arguments match the default value, the result of Rebecca's rsvp is the same.
You removed the `inviteOnly` argument from Nadia's rsvp. Since the default
value of `inviteOnly` is `true`, the result of Nadia's rsvp is the same.
You removed the `partySize` argument from Tony's rsvp. If Tony had an
invitation, the default value of `partySize` would be used in the RSVP.
You removed the `allergies` argument from both Linh and Noor's rsvps. Their
rsvps will display the default value of `none` for "Allergies".
Save and run the code to observe the following output:
```txt
Sorry, Tony is not on the guest list
Total RSVPs:
Name: Rebecca, Party Size: 1, Allergies: none
Name: Nadia, Party Size: 2, Allergies: Nuts
Name: Linh, Party Size: 2, Allergies: none
Name: Noor, Party Size: 4, Allergies: none
Name: Jonte, Party Size: 2, Allergies: Stone fruit
```
Notice that the default values are used in place of omitted arguments, such as
`partySize` and `allergies`.
- [Program.cs](./rsvp_app/Program.cs)
### Recap
Here's what you've learned about optional and named arguments so far:
- Parameters are made optional by setting a default value in the method
signature.
- Named arguments are specified with the parameter name, followed by a colon
and the argument value.
- When combining named and positional arguments, you must use the correct order
of parameters.
---
## Exercise
### Complete the challenge to display email addresses
Code challenges reinforce what you've learned, and help you gain some
confidence before continuing on.
The focus of this challenge is to create a method with the proper parameters,
including an optional parameter.
### Display email addresses
Your challenge is to create a method that displays the correct email address
for both internal and external employees. You're given lists of internal and
external employee names. An employee's email address consists of their username
and company domain name.
The username format is the first two characters of the employee first name,
followed by their last name. For example, an employee named "Robert Bavin"
would have the username "robavin". The domain for internal employees is
"contoso.com".
In this challenge, you're given some starting code. You must decide how to
create and call a method to display email addresses.
### Code challenge: Add a method to display email addresses
In the code you start with, there are two arrays for internal and external
employees. Remember, the domain for internal employees is "contoso.com" and the
username for all employees is the first two characters of their first name,
followed by their full last name.
Your challenge is to create a method that will display the email address of
internal and external employees. The method should include an optional
parameter for the domain name of external employees.
Copy and paste the following code into the code editor.
```cs
string[,] corporate = {
{"Robert", "Bavin"}, {"Simon", "Bright"},
{"Kim", "Sinclair"}, {"Aashrita", "Kamath"},
{"Sarah", "Delucchi"}, {"Sinan", "Ali"}
};
string[,] external = {
{"Vinnie", "Ashton"}, {"Cody", "Dysart"},
{"Shay", "Lawrence"}, {"Daren", "Valdes"}
};
string externalDomain = "hayworth.com";
for (int i = 0; i < corporate.GetLength(0); i++) {
// display internal email addresses
}
for (int i = 0; i < external.GetLength(0); i++) {
// display external email addresses
}
```
Update the code to use a method to display the email addresses according to the
challenge specifications.
Use what you've learned about using parameters and optional arguments to
complete the update.
Verify that your code produces the following output:
```txt
robavin@contoso.com
sibright@contoso.com
kisinclair@contoso.com
aakamath@contoso.com
sadelucchi@contoso.com
siali@contoso.com
viashton@hayworth.com
codysart@hayworth.com
shlawrence@hayworth.com
davaldes@hayworth.com
```
Whether you get stuck and need to peek at the solution or you finish
successfully, continue on to view a solution to this challenge.
- [Program.cs](./disp_mail_addr/Program.cs)
---
### Summary
Your goal was to learn more about using parameters in methods and to understand
method scope. You learned about value and reference types and how data is
affected inside of a method. You also learned how to use named and optional
arguments to extend your method's capabilities.

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string[,] corporate = {
{"Robert", "Bavin"}, {"Simon", "Bright"},
{"Kim", "Sinclair"}, {"Aashrita", "Kamath"},
{"Sarah", "Delucchi"}, {"Sinan", "Ali"}
};
string[,] external = {
{"Vinnie", "Ashton"}, {"Cody", "Dysart"},
{"Shay", "Lawrence"}, {"Daren", "Valdes"}
};
const string external_domain = "hayworth.com";
const string internal_domain = "contoso.com";
for (int i = 0; i < corporate.GetLength(0); i++) {
display_email(corporate[i, 0], corporate[i, 1], internal_domain);
}
for (int i = 0; i < external.GetLength(0); i++) {
display_email(external[i, 0], external[i, 1], external_domain);
}
void display_email(string first, string last, string domain=internal_domain) {
string username = first.Substring(0, 2) + last;
username = username.ToLower();
Console.WriteLine($"{username}@{domain}");
}

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028_method_parameters/disp_mail_addr/disp_mail_addr.csproj Normal file
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<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net8.0</TargetFramework>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
</PropertyGroup>
</Project>

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028_method_parameters/rsvp_app/Program.cs Normal file
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string[] guest_list = {"Rebecca", "Nadia", "Noor", "Jonte"};
string[] rsvps = new string[10];
int count = 0;
// void RSVP(string name, int party_size, string allergies, bool invite_only) {
void RSVP(string name,
int party_size = 1,
string allergies = "none",
bool invite_only = true) {
if (invite_only) {
bool found = false;
foreach (string guest in guest_list) {
if (guest.Equals(name)) {
found = true;
break;
}
}
if (!found) {
Console.WriteLine($"Sorry, {name} is not on the guest list");
return;
}
}
rsvps[count] = $"Name: {name}," +
$"\tParty Size: {party_size}," +
$"\tAllergies: {allergies}";
count++;
}
void show_RSVPs() {
Console.WriteLine("\nTotal RSVPs:");
for (int i = 0; i < count; i++){
Console.WriteLine(rsvps[i]);
}
}
//RSVP("Rebecca", 1, "none", true);
RSVP("Rebecca");
RSVP("Nadia", 2, "Nuts");
//RSVP("Linh", 2, "none", false);
RSVP(name: "Linh", party_size: 2, invite_only: false);
RSVP("Tony", 1, allergies: "Jackfruit", invite_only: true);
RSVP("Noor", 4, invite_only: false);
RSVP("Jonte", 2, "Stone fruit", false);
show_RSVPs();

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<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net8.0</TargetFramework>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
</PropertyGroup>
</Project>