This C# Online Test
Separates Good From Bad Hires

A company is designing the class hierarchy for various cache implementations:

public class Cache {}

public class DiskCache : Cache {}

public class MemoryCache : Cache {}

public class OptimizedDiskCache : DiskCache {}

Select all the answers that will result in a runtime exception.

Refactor the AlertService and AlertDAO classes:

• Create a new interface, named IAlertDAO, that contains the same methods as AlertDAO.
• AlertDAO should implement the IAlertDAO interface.
• AlertService should have a public constructor that accepts IAlertDAO.
• The RaiseAlert and GetAlertTime methods should use the object passed through the constructor.

Implement the UniqueNames method. When passed two arrays of names, it will return an array containing the names that appear in either or both arrays. The returned array should have no duplicates.

For example, calling MergeNames.UniqueNames(new string[]{'Ava', 'Emma', 'Olivia'}, new string[]{'Olivia', 'Sophia', 'Emma'}) should return an array containing Ava, Emma, Olivia, and Sophia in any order.

Implement the function FindRoots to find the roots of the quadratic equation: ax² + bx + c = 0. The function should return a tuple containing roots in any order. If the equation has only one solution, the function should return that solution as both elements of the tuple. The equation will always have at least one solution.

The roots of the quadratic equation can be found with the following formula:

For example, FindRoots(2, 10, 8) should return (-1, -4) or (-4, -1) as the roots of the equation 2x² + 10x + 8 = 0 are -1 and -4.

User interface contains two types of user input controls: TextInput, which accepts all characters and NumericInput, which accepts only digits.

Implement the class TextInput that contains:

• Public method void Add(char c) - adds the given character to the current value
• Public method string GetValue() - returns the current value

Implement the class NumericInput that:

• Inherits TextInput
• Overrides the Add method so that each non-numeric character is ignored

For example, the following code should output "10":

TextInput input = new NumericInput();
input.Add('1');
input.Add('a');
input.Add('0');
Console.WriteLine(input.GetValue());

Using only NUnitLite 1's Assert.AreEqual method, write tests for the Account class that cover the following cases:

• The Deposit and Withdraw methods will not accept negative numbers.
• Account cannot overstep its overdraft limit.
• The Deposit and Withdraw methods will deposit or withdraw the correct amount, respectively.
• The Withdraw and Deposit methods return the correct results.

public class Account
{
    public double Balance { get; private set; }
    public double OverdraftLimit { get; private set; }

    public Account(double overdraftLimit)
    {
        this.OverdraftLimit = overdraftLimit > 0 ? overdraftLimit : 0;
        this.Balance = 0;
    }

    public bool Deposit(double amount)
    {
        if (amount >= 0)
        {
            this.Balance += amount;
            return true;
        }
        return false;
    }

    public bool Withdraw(double amount)
    {
        if (this.Balance - amount >= -this.OverdraftLimit && amount >= 0)
        {
            this.Balance -= amount;
            return true;
        }
        return false;
    }
}

Each of the test case methods should be in the Tester class and have the Test attribute.

Each account on a website has a set of access flags that represent a users access.

Update and extend the enum so that it contains three new access flags:

1. A Writer access flag that is made up of the Submit and Modify flags.
2. An Editor access flag that is made up of the Delete, Publish and Comment flags.
3. An Owner access that is made up of the Writer and Editor flags.

For example, the code below should print "False" as the Writer flag does not contain the Delete flag.

Console.WriteLine(Access.Writer.HasFlag(Access.Delete))

Implement methods and properties in the DecoratorStream class:

• Write method should write the prefix into the underlying stream member only on the first Write invocation. It should always write the bytes it receives to the underlying stream.
• The prefix should be written in UTF-8 encoding.

For example, if the DecoratorStream is instantiated with "First line: " as the prefix parameter and Write method is called with UTF-8 byte representation of "Hello, world!", it should write "First line: Hello, world!" into the underlying stream.

Implement a function FolderNames, which accepts a string containing an XML file that specifies folder structure and returns all folder names that start with startingLetter. The XML format is given in the example below.

For example, for the letter 'u' and XML file:

<?xml version="1.0" encoding="UTF-8"?>
<folder name="c">
    <folder name="program files">
        <folder name="uninstall information" />
    </folder>
    <folder name="users" />
</folder>

the function should return "uninstall information" and "users" (in any order).