Whenever you explicitly specify a value in a program instead of referencing a variable or other form of data, that value is called a literal. In the initialization example above, 3 is a literal. Numbers can be written as integers, decimal fractions, “scientific” or hexadecimal notation. To identify a hexadecimal number, simply precede it with &H. You can also declare multiple variables with a single statement: some words are reserved as keywords in the language, and these cannot be used as variable names or as names of anything else. I tend to use the con prefix with constants to remind myself that I`d better not try to change it. Here is an example of declaring a constant: In Lesson 8, we understood the concept of data and how to handle it in Visual Basic 2017. In this lesson, we will learn how to store and declare data. In Visual Basic 2017, data can be stored as variables or constants. Variables are like mailboxes in mail. The contents of variables change from time to time, as do mailboxes. In Visual Basic 2017, variables are the specific ranges allocated by the computer`s memory to store data. Use the following rules when naming procedures, constants, variables, and arguments in a Visual Basic module: Like most programming languages, Visual Basic can use and process named variables and their contents.
Variables are more simply described as names we use to refer to a location in memory – a place that contains a value we are working with. Visual Basic is not case-sensitive, but it is case-sensitive in the statement in which the name is declared. All variables in Visual Basic are typed, including those declared as Variant. If you do not specify the type, the compiler uses Variant. A Variant variable can contain data of any type. After you declare variables, you can assign a value to a variable later by using a statement similar to the following: There are other, more complex statements that can span multiple lines of code: The naming rules for variables also apply to other language constructs, such as function names and module names. In Visual Basic it is not possible to combine declaration and initialization with variables (because VB does not support constructors – see Objects and initialization), the following statement is illegal: Another, less obvious type conversion error is as follows: In general, you should not use names that match the names of functions. intrinsic instructions, methods, and constants. that are used in Visual Basic or by the host application. Otherwise, the same keywords are shaded in the language. To use an intrinsic function, statement, or method that conflicts with an assigned name, you must explicitly identify it. Precede the intrinsic name of the function, statement, or method with the name of the associated type library.
For example, if you have a variable named Left, you can only call the Left function using VBA. Left. In Visual Basic 2017, you must declare variables before you use them. To declare a variable, you must give it a name and specify its data type. If you do not, the program will encounter an error. Variables are typically declared in the general section of code windows using the Dim statement. You cannot repeat names in the same range level. For example, you cannot declare two variables named age in the same procedure. However, you can declare a private variable named age and a procedure-level variable named age in the same module.
In addition, most variables created in a procedure are ignored by Visual Basic when the procedure closes. However, the Static keyword retains the value of a variable even after the procedure is complete. Finally, the Public keyword declares a global variable, which means that it can be used by all procedures and modules in the entire Visual Basic 2015 program. Like mailboxes, each variable must be given a name. To name a variable in Visual Basic 2017, you must follow a set of rules as follows: We recommend that you get used to using descriptive variable names. If you look at a piece of code several months after it`s created and see the variables var1, var2, etc., you`ll probably have no idea what they control. Variable names like text input or time_start are much more descriptive – you know exactly what they do. If you have a variable name consisting of multiple words, it is common to start the next word with an uppercase letter. Keep in mind that you cannot use spaces in variable names and that meaningful capitalization makes it easier to distinguish between words. If you enter the variable name later in the code, you can type everything in lowercase – once you leave the line in question, VB, if the variable name is valid, will capitalize it accordingly. In addition, there are certain groups of names that, although not linguistic keywords, are reserved for one reason or another.
In Visual Basic, variables can be declared anywhere in a subroutine, function, or property, but their scope is limited to that routine. They can also be declared in the Declarations section of a module before any subroutine, function, or property if they have a module-level scope. x is a subroutine that accepts two string arguments. The Call keyword is a remnant of older versions of Basic. If you are using this form, you must enclose the full list of arguments in parentheses. Sometimes the programmer wants to call a function, but is not interested in the return value only for side effects. In such cases, he or she will call the function as if it were a subroutine, but only the first form above can be used. Here are some examples of assigning valid variables: The above keywords indicate the scope of the declaration. First, the Private keyword declares a local variable or local variable to a procedure or module. However, the Private keyword is rarely used, usually we use the Dim keyword to declare a local variable. On the other hand, the Static keyword declares a variable that is used multiple times, even after a procedure is completed.
Variable names in Visual Basic consist of letters (case-sensitive) and numbers. The underscore “_” is also allowed. Names cannot begin with a number. Names can be of any length. Like mailboxes, each variable must be given a name. To name a variable in VB 2015, you must follow a number of rules. Here are the following rules when naming variables in Visual Basic 2015: After declaring different variables using Dim statements, we can assign values to those variables. The syntax for an assignment in Visual Basic 2015 is The first word (debugging) is the name of an object that is built into Visual Basic. The second word (print) is the name of a method of this object. “Hello World” is the argument of the method. The result is: Thus, the value of the expression to the right of the equal sign (=) is assigned to the variable on the left.
The above expression can be: Typically, VB specifies the access_type of a variable with the keyword Dim (note that the author actually remembers where this term came from). When we assign a variable name, type, and access_type, we observe the following variable declaration statements: Note that you can assign a value to the string on one row by using the = sign instead of declaring the variable, and then assign it a value on another row. *You can also declare a variable by assigning it an initial value, as shown in the following examples: This is not a good idea because it is too easy to forget that in Visual Basic the type name applies only to the immediately preceding variable name. The example declares two variants and an integer 2 The use of the terms elementary (i.e. simple) and complex to describe data types is somewhat misleading. It is true that a tank type is a simple type and that an array is relatively complex. However, one would certainly be right to say that a double is not so easy of one type. The fact is that value types can be considered less complex than reference types in VB. Of course, the hole in this theory is the definition of structure, which is a type of value.
For more information about value and reference types, see the Microsoft MSDN Web site here. You can also combine the above statements on a line and separate each variable with a comma as follows: In the context of a programming language, we can formally define a variable as an object with the following attributes: By default, if no initial value is assigned when declaring variables, VB initializes all variables to zero or a value similar to zero. Therefore, integer types have a default value of 0, Double a default value of 0.0, and string types have a default value of Nothing. In terms of string types, it is important to note that Nothing, the empty string (“”) and a string containing a space (“” “) are very different objects. Nothing has length because it is not an existing object (it is a null reference). The empty string (“”) is an object that contains essentially nothing, and therefore has a length of zero. Finally, a string containing a space (” ” “) has a length of one. If you want to declare additional variables, you can declare them on separate lines or combine several variables on a single line and separate each variable with a comma as follows: If an explicit data type conversion is to be performed, VB provides many type conversion methods that allow for a “valid” conversion. One of these method classes is the Convert1 class. The Convert class provides many methods for converting one base type to another base type, such as a duplicate integer. The general format is as follows: Take a look at some examples of variable arithmetic: Some examples of valid and invalid variable names are listed in Table 9.1. You can also assign the value of another variable to a variable, as follows: In Visual Basic, variables can be declared before they are used, or the programmer can ask the compiler to allocate memory to them.
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