vb.net compound assignment

Our "Hello, world" program illustrated the basic structure of a VB.NET program, but we will need a slightly more elaborate example to show the use of other basic programming constructs, such as variables , expressions, and control structures. The example illustrates a number of features, which we will explain later. Our next example is a simple calculator for an IRA account. We calculate the accumulation of deposits to an IRA of $2000.00 a year at 6% interest for 10 years , assuming that each deposit is made at the end of the year. Our calculation is performed in two ways:

The example program is in the folder Ira\Step1 .

If you compile and run it, you will see this output:

In VB.NET variables are always of a specific data type. Some common types are Integer for integers and Double for floating-point numbers . VB.NET has the Decimal data type, which has a high degree of precision, suitable for financial calculations.

You must declare variables before you use them, and you may optionally initialize them.

If an initial value is not specified in the declaration, the variable is automatically initialized . For example, an uninitialized Decimal variable is set to zero. We will discuss initialization later in the chapter.

Variables must be either local within a method or members of a class. There are no global variables in VB.NET.

A literal is used when you explicitly write a value in a program rather than represent it with a variable name . An integer literal is represented by an ordinary base-10 integer, an octal integer, or a hexadecimal integer. An octal integer is indicated with the &O prefix, such as &O77 (which is 63 in base 10). A hexadecimal literal is indicated with the &H prefix, such as &H7FFF (which is 32,767 in base 10). The suffixes S , I , and L are used to designate Short, Integer, and Long. A floating-point literal is represented by a number with a decimal point or by exponential notation. You may determine the type that is used for storing a literal by a suffix. The suffix F indicates single precision (32-bit) floating point. The suffix R indicates double precision (64-bit) floating point. The Single and Double types are often suitable for scientific and engineering purposes. The suffix D indicates Decimal , which is usually more suitable for financial calculations, and it represents a high precision (128-bit) fixed-point number.

A character string literal is represented by a sequence of characters in double quotes.

You can combine variables and literals via operators to form expressions. The VB.NET operators are similar to those in other .NET languages.

One of the newest features of VB.NET is its new compound assignment operators that perform arithmetic operations as part of the assignment. Here are examples from the Ira program:

There are six new compound assignment operators available in VB.NET. They are demonstrated in the following example:

There is also a compound assignment operator for string concatenation. The following expression concatenates an exclamation point to the end of the string contained in the variable buf:

Precedence rules determine the order in which operators within expressions are evaluated. Operators are applied in the precedence order shown in Table 3-1. Operators within a row have equal precedence. For operators of equal precedence within the same expression, the order of evaluation is from left to right, as they appear in an expression. Order of evaluation can be explicitly controlled by using parentheses.

Table 3-1. Operator Precedence in VB.NET

Output and Formatting

The Console class in the System namespace supports two simple methods for performing output:

WriteLine writes out a string followed by a new line.

Write writes out just the string without the new line.

You can write out other data types by relying on the ToString method of System.Object , which will provide a string representation of any data type. System.Object is the base class from which all classes inherit. We will discuss this class in Chapter 6, where you will also see how to override ToString for your own custom data types. You can use the string concatenation operator & to build up an output string.

The output is all on one line:

Placeholders

A more convenient way to build up an output string is to use placeholders such as {0}, {1}, and so on. An equivalent way to do the output shown above is

The program OutputDemo illustrates the output operations just discussed.

We will generally use placeholders for our output from now on. Placeholders can be combined with formatting characters to control output format.

Format Strings

VB.NET has extensive formatting capabilities, which you can control through placeholders and format strings.

Simple placeholders: {n}, where n is 0, 1, 2, , indicating which variable to insert

Control width: {n,w}, where w is width (positive for right justified and negative for left justified) of the inserted variable

Format string: {n:S}, where S is a format string indicating how to display the variable

Width and format string: {n,w:S}

A format string consists of a format character followed by an optional precision specifier . Table 3-2 shows the available format characters.

Table 3-2. Format Characters

Sample Formatting Code

The sample program in Ira\Step1 provides an example. The header uses width specifiers, and the output inside the loop uses width specifiers and the currency format character.

Control Structures

The preceding code fragment illustrates a While End While loop. VB.NET supports several control structures, including the If and Select decision statements as well as For and While loops .

While End While

Do While Loop

Do Until Loop

Do Loop While

Do Loop Until

For Each Next

If Then End If

If Then Else End If

If Then ElseIf Then End If

Select Case End Select

With End With

SyncLock End SyncLock

Try Catch Finally

Most of these will be familiar to Visual Basic programmers. The Throw and Try statements are used in exception handling. We will discuss exceptions later in this chapter. The SyncLock statement can be used to enforce synchronization in multithreading situations. We will discuss multithreading in Chapter 10.

Select Case Statement

A Select Case statement is used to execute one of several groups of statements, depending on the value of a test expression. The test expression must be one of the following data types: Boolean , Byte , Char , Date , Double , Decimal , Integer , Long , Object , Short , Single , or String .

After a particular case statement is executed, control automatically continues after the following End Select . The program SelectDemo illustrates use of the Select Case statement in VB.NET.

Our Ira\Step1 example program has a method IraTotal for computing the total IRA accumulation by use of a formula. In VB.NET, every function is a method of some class or module; there are no freestanding global functions. If a method does not refer to any instance variables of the class, the method can be declared as Shared . We will discuss instance data of a class later in this chapter. If a method is accessed only from within a single class, it may be designated as Private . Note the use of the Private keyword in the Ira\Step1 example. The Shared keyword is not used however, since the example uses a module instead of a class. All methods in a module are shared by default.

Also in the Ira\Step1 example, note the use of the Pow and Round methods of the Math class, which is another class in the System namespace. These methods are shared methods. To call a shared method from outside the class in which it is defined, place the name of the class followed by a period before the method name.

Console Input in VB.NET

Our first Ira program is not too useful, because the data are hardcoded. To perform the calculation for different data, you would have to edit the source file and recompile. What we really want to do is allow the user of the program to enter the data at runtime.

An easy, uniform way to do input for various data types is to read the data as a string and then convert it to the desired data type. Use the ReadLine method of the System.Console class to read in a string. Use the ToXxxx methods of the System.Convert class to convert the data to the type you need. This can be seen in the Ira\Step2 example.

Although console input in VB.NET is fairly simple, we can make it even easier using object-oriented programming. We can encapsulate the details of input in an easy-to-use wrapper class, InputWrapper (which is not part of VB.NET or the .NET Framework class library, and was created for this book).

Using the Inputwrapper Class

In VB.NET, you instantiate a class by using the New keyword.

This code creates the object instance iw of the InputWrapper class.

The InputWrapper class wraps interactive input for several basic data types. The supported data types are int , double , decimal , and string . Methods getInt , getDouble , getDecimal , and getString are provided to read those types from the command line. A prompt string is passed as an input parameter. The directory InputWrapper contains the files InputWrapper.vb , which implements the class, and TestInputWrapper.vb , which tests the class. (For convenience, we provide the file InputWrapper.vb in each project where we use it.)

You can use the InputWrapper class without knowing its implementation. With such encapsulation, complex functionality can be hidden by an easy-to-use interface. (A listing of the InputWrapper class is in the next section.)

Here is the code for Ira\Step2 . We read in the deposit amount, the interest rate, and the number of years, and we compute the IRA accumulation year by year. The first input is done directly, and then we use the InputWrapper class. The bolded code illustrates how to use the InputWrapper class. Instantiate an InputWrapper object iw by using new . Prompt for and obtain input data by calling the appropriate getXXX method.

Inputwrapper Class Implementation

The InputWrapper class is implemented in the file InputWrapper.vb . You should find the code reasonably intuitive, given what you already know about classes.

Note that, unlike the method IraTotal , the methods of the InputWrapper class are used outside of the class so they are marked as public .

If bad input data is presented, an exception will be thrown. Exceptions are discussed in Chapter 5.

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IDE0054 "Use compound assignment" false positive in object initializer #33382

dgrunwald commented Feb 14, 2019

jnm2 commented Mar 9, 2019

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ICompound Assignment Operation Interface

Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.

Represents a compound assignment that mutates the target with the result of a binary operation.

Current usage: (1) C# compound assignment expression. (2) VB compound assignment expression.

This node is associated with the following operation kinds:

• CompoundAssignment

This interface is reserved for implementation by its associated APIs. We reserve the right to change it in the future.

Extension Methods

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Multiassignment in VB like in C-Style languages

Is there a way to perform this in VB.NET like in the C-Style languages:

• variable-assignment
• c#-to-vb.net

• 1 Is there any advantage of the multiple assignment versus performing each assignment individually? Many translator applications will optimize the two to be equal at run-time. –  Thomas Matthews Commented Feb 22, 2010 at 18:29
• Yes, there is an advantage. If you want to assign a specific value, say 1.7834 to H(I) and W(J), you have to type 1.7834 only once, effectively treating it as a 1-time constant, whereas typing it twice, it's not obvious that the two constants, although equal, are the same constant. E.g., if H & W are the height and width, it could be a coincidence that the height & width are equal or they might always represent a square. –  Chelmite Commented Jun 18, 2013 at 23:42

2 Answers 2

Expanding on Mark's correct answer

This type of assignment style is not possible in VB.Net. The C# version of the code works because in C# assignment is an expression which produces a value. This is why it can be chained in this manner.

In VB.Net assignment is a statement and not an expression. It produces no value and cannot be changed. In fact if you write the code "a = b" as an expression it will be treated as a value comparison and not an assignment.

Eric's recent blog post on this subject for C#

• http://blogs.msdn.com/ericlippert/archive/2010/02/11/chaining-simple-assignments-is-not-so-simple.aspx

At a language level assignment is a statement and not an expression.

• For info, it is a wishlist item to add support for this: blogs.msdn.com/lucian/archive/2010/02/12/… –  Rowland Shaw Commented Mar 2, 2010 at 17:13

As soon as I post this, someone will provide an example of how to do it. But I don't think it is possible . VB.NET treats the single equals in the r-value as a comparison. For example:

The above code prints 0 (false) and -1 (true).

• 1 It's not possible. Here's where Lucian, who leads the VB.Net specification, blogs about whether it's worth adding. blogs.msdn.com/lucian/archive/2010/02/12/… For bonus marks here's Eric Lippert (works on C# compiler) blogging about how confusing it is in C#. blogs.msdn.com/ericlippert/archive/2010/02/11/… –  MarkJ Commented Feb 22, 2010 at 17:13

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