​​Foreach Loop in C# (part 2)

Important Points:

🔸 The foreach loop iterate only in forward direction.

🔸 Performance wise foreach loop takes much time as compared with for loop.

🔸 Because internally it uses extra memory space as well as.

🔸 The foreach loop use GetEnumarator() method of the IEnumerable interface. So, the foreach loop can be used with any class that has implemented the interface.

🔸 Exit the foreach loop by using break, return, Goto and throw.

The following example demonstrates the foreach loop on a dictionary collection.

​​Foreach Loop in C# (part 3)

As mentioned before, the foreach loop can be used to iterate any class that has implemented the IEnumerable interface. The following example demonstrates how to implement the IEnumerable interface in order to use the foreach loop with the custom class.

Above, the Shop class has implemented the IEnumerable interface that contains the GetEnumerator() method. This will enable the Shop class to be used with the foreach loop that returns the Customer objects.

​​Foreach Loop in C# (part 4)

Beginning with C# 8.0, you can use the await foreach statement to consume an asynchronous stream of data, that is, the collection type that implements the IAsyncEnumerable<T> interface. Each iteration of the loop may be suspended while the next element is retrieved asynchronously. The following example shows how to use the await foreach statement:

You can also use the await foreach statement with an instance of any type that satisfies the following conditions:

🔸 A type has the public parameterless GetAsyncEnumerator method. That method can be a type's extension method.

🔸 The return type of the GetAsyncEnumerator method has the public Current property and the public parameterless MoveNextAsync method whose return type is Task<bool>, ValueTask<bool>, or any other awaitable type whose awaiter's GetResult method returns a bool value.

By default, stream elements are processed in the captured context. If you want to disable capturing of the context, use the TaskAsyncEnumerableExtensions.ConfigureAwait extension method. For more information about synchronization contexts and capturing the current context, see Consuming the Task-based asynchronous pattern. For more information about asynchronous streams, see the Asynchronous streams section of the What's new in C# 8.0 article.

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​​How to loop through an enum in C#? (part 1)

Here you will learn how to enumerate or loop through an enum.

In C#, an enum is used to assign constant names to a group of numeric integer values. It makes constant values more readable, for example, WeekDays.Monday is more readable than number 0 when referring to the day in a week.

An enum can be looped through using Enum.GetNames<TEnum>(), Enum.GetNames(), Enum.GetValues<TEnum>(), or Enum.GetValues() static methods with the foreach loop.

The following example gets the names of an enum using the Enum.GetNames<TEnum>() method.

​​How to loop through an enum in C#? (part 2)

The Enum.GetValues<TEnum>() is a static method that retrieves an array of the constant values of the specified enum.

The following example shows how to get the values of an enum using the Enum.GetValues<TEnum>() method.

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​​NullReferenceException in C# (part 1)

The NullReferenceException is an exception that will be thrown while accessing a null object.

The following example shows the code that throws the NullReferenceException:

In the above example, a NullReferenceException will be thrown in the DisplayCities() function while accessing cities list using a foreach loop because the cities list is null. If the caller of the DisplayCities() function pass a null IList value then it will raise a NullReferenceException.

​​Solutions to fix the NullReferenceException (part 2)

To prevent the NullReferenceException exception, check whether the reference type parameters are null or not before accessing them.

Solution 1: Check whether an object contains a null value or not using an if condition, as shown below:

In the above example, if(cities == null) checks whether the cities object is null or not. If it is null then display the appropriate message and return from the function.

​​Solutions to fix the NullReferenceException (part 3)

In .NET 5, use the null conditional operator ?., as shown below:

In the above example, std?.FirstName is like if(std != null) std.FirstName. The std?.FirstName checks if std is not null then only access the FirstName property.

​​Solutions to fix the NullReferenceException (part 4)

In .NET 4.x and above versions, use Null-Coalescing operator ?? to prevent an exception, as shown below:

In the above example, ?? is a null coalescing operator that checks if an object is null or not, if it is null then create an object. The cities ?? new List<string>() creates a new list object if a cities is null in foreach loop. Thus, the NullReferenceException will be not be raised.

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​​Generate Random Numbers in C# (part 1)

Here you will learn how to generate random numbers in C#.

C# provides the Random class to generate random numbers based on the seed value. Use the following methods of the Random class to generate random numbers.

The following example demonstrates how to generate a random integers.

Call the Next() method multiple times to get the multiple random numbers, as shown below.

​​Generate Random Numbers in Range

Use the Next(int) method overload to generate a random integer that is less than the specified maximum value.

The following example generates the positive random numbers that are less than 10.

​​Generate Random Number in Min to Max Range

Use the Next(int min, int max) overload method to get a random integer that is within a specified range.

In the above example, rnd.Next(10, 20) generate random numbers that will be between 10 to 19.

​​Generate Random Floating Point Number

Use the NextDouble() method to get a random floating-point number between 0.0 to 1.0, as shown below.

​​Seed Value

The Random class uses the seed value as a starting value for the pseudo-random number generation algorithm. By default, the Random class uses the system clock to generate its seed value so that each instance of the Random class can generate different random numbers.

Two different instances of the Random class having the same seed value will generate the same random numbers, as shown below.

In the above example, two different objects of the Random class are instantiated with the same seed value. So, they will generate the same random numbers.

By default, the seed value is time-dependent. In .NET Core, the default seed value is produced by the thread-static, pseudo-random number generator.

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​​Default Value of Auto-Implemented Property

In C# 6.0 or higher versions, assign the inline default value to the auto-implemented property, as shown below.

​​Using Property Setter

The following example sets the default value to a private property field.

​​Using DefaultValue Attribute

You can assign the default value using the DefaultValueAttribute attribute, as shown below.

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​​In C#, the Scope of the variable determines the accessibility of the variable to a particular part of the application. Variables can be declared within the class, method, and code block of a loop, condition, etc.

There are three types of scopes in C#.

- Class Level Scope
- Method Level Scope
- Code-Block Level Scope

Class Level Scope

A variable declared within a class is known as a field. It has a class-level scope that can be accessed anywhere in the class, such as class methods, properties, etc.

In the above example, the Student class contains two class variables (a.k.a. fields) _firstName and _lastName. These fields can be accessed anywhere within the class, i.e., within any non-static methods and properties.

The class level variables can also be accessed out of class using class objects depending on the access modifiers. The static variables of the class can only be accessed from the static methods or properties.

​​Method Level Scope

A variable declared within a method has a method level Scope. It is also known as a local variable of the method where it is declared. It cannot be accessed outside the method.

Any nested code blocks within the method can access this type of variable. It cannot be declared twice with the same name within the same scope.

The local variable's scope ends when the method execution completes, and they will be collected by the garbage collector.

The following example shows the method Level scope.

In the above example, the Main() method can only access variables declared in the Main() method but not variables of other methods. In the same way, the Process() method cannot access variables declared in the Main() or any other method.

​​Code-Block Level Scope

A variable declared within a loop or any block within brackets has the code-block level scope. A variable declared within a loop or code block cannot be accessed outside of it, whereas a variable declared outside of the loop can be accessible within the loop.

In the above example, a variable i declared within a for loop. So, it can only be accessed within the for loop block and cannot be accessed outside for loop. In the same way, x is declared within the if block, so it can only be accessed in that block but not outside of it.

A variable must be declared outside of the code block to make it accessible to outside code.

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