In VB.NET, the Select Case statement is a collection of multiple Case statements that allows you to execute a single Case statement from the list of statements. A selected case statement uses a variable to test the equality of multiple cases or statements in a program. If the variable corresponds to test cases, this statement is executed. And if the condition does not match any case, the default statement is executed. The diagram above shows that if the defined condition is true, statement_1 is executed, and if the condition is false, statement_2 is executed. The While loop consists of three parts: initialization, testing, and updating. Each execution of the statement is called a cycle. A value is read from the console. We can only use digital data. The keywords Try, Catch, End Try are used for exception handling. If an exception is thrown, the statements are executed after the Catch keyword. The End statement terminates the program.
Other Control Structures Describes the control structures used for resource disposal and object access. The Select statement is a selection control statement. It allows the value of a variable or expression to control the flow of program execution through a multipathic branch. It creates multiple branches in an easier way than combining If, Else If statements. Unregulated, a program reviews its records from start to finish. Some very simple programs can only be written with this one-way stream. However, much of the power and usefulness of any programming language lies in the ability to change the order of execution with control instructions and loops. The statements that make up the core of the language are actually very few. The flexibility of each programming language is based on its ability to change the order in which instructions are executed through a series of so-called flow control instructions.
These are the statements that literally make decisions and react differently based on data, user actions, or external conditions. In this chapter, you will learn, among other things, how to do the following: You can also execute multiple statements separated by colons: If this condition is true in the flowchart of the if-else-if statement, the statement is executed in the if block. If the condition is not true, it passes the check to the next ElseIf condition to verify that the condition matches. And if none of the conditions are met, the else block is executed. The While statement is a control flow statement that allows code to be executed repeatedly based on a specific Boolean condition. where condition is a Boolean or relational condition and statement(s) is a simple or compound statement. An example of an If-Then statement is − The Exit statement can be used to terminate blocks defined by While, For, or Select statements. The Select Sensitivity structure compares an expression to different values.
The advantage of the Select Case statement over multiple Ifs. Then. Another statement is that it makes the code easier to read and maintain. We have a variable num. He is assigned 31. The If keyword searches for a Boolean phrase. The expression is enclosed in square brackets. 31 > 0 is true, so the statement is executed inside the block.
Visual Basic has an optional Step keyword. It controls how the counter variable is increased or decreased. “Another variant of the If. Th~n . The Else statement uses several conditions with the Else-If keyword: VB.NET provides the following conditional or decision statements. Using the For Each statement is simple. The planets are the network through which we iterate. The planet is a temporary variable that has the current value of the table. The For Each statement traverses all the planets and passes them to the console. Applications need a mechanism to test conditions and take a different approach depending on the test result. Visual Basic provides three such decision or condition statements: You may have noticed that the order of the comparison in a If .
nested. Second, a structure that uses Elself declarations. If you had written the previous code segment with the first two conditions as follows: In fact, the statements discussed in the first half of this chapter are what programming is. Without the ability to control the flow of the program, computers would be just cumbersome calculators. You`ve seen in previous chapters how to use the If statement to modify the execution flow, and I assume you`re somewhat familiar with these types of statements. This section provides a formal explanation of the flow control instructions. These declarations are divided into two main categories: decision statements and loop declarations. We initiate the i counter to zero. The Next statement increments the counter by one until it is equal to 9. In the program above, we enter two numbers to find the largest number with the relational operator.
And if the first number is greater than the other, the first statement is executed; Otherwise, the second statement is executed. The Select Case structure tests a single expression that evaluates once at the beginning of the structure. The test result is then compared to several values, and if it matches one of them, the corresponding instruction block is executed. The following is the syntax for the Select Case statement: Some Case statements may be followed by multiple values separated by commas. Here is a revised version of the previous example: We can use the control flow statement to regulate the program execution flow. We can use control trees to write Visual Basic code that makes decisions or repeats actions. Nested control trees Covers control structures within other control structures. If the number of cycles before the loop launch is known, we can use the For Next instructions.
In this construction, we declare a counter variable whose value is automatically increased or decreased each time the loop is repeated. The For Each construct facilitates the iteration of data collections. It does not have an explicit counter. The For Each statement traverses the array or collection one at a time, and the current value is copied to a variable defined in the construct. A variant of the If. Then the statement is the if. Then. An Else statement that executes one block of statements if the condition is True and another if the condition is False. The syntax of If. Then.
The Else statement is: Of course, the Select Case statement cannot be replaced by If. Then the structures. The Select Case structure evaluates the expression only at the beginning. B. On the other hand, the if. Then. The Else structure can evaluate a different expression for each ElseIf statement. When you use the select-case statement in VB.NET program, you can override the use of multiple If-Then-Else statements in the program to improve readability and ease of use. In the If-Then statement, the condition can be Boolean, logical, or relational, and the statement can be a single statement or a group of executed statements if the condition is true. The five working days and two weekend days are processed by two multi-value case reports. This structure does not contain a Case Else statement because the values of the Case statements are examined.
The WeekDay() function cannot return any other values. What makes programming languages so flexible and able to handle any programming situation and challenge with a relatively small set of commands is their ability to examine external or internal conditions and act accordingly. Programs are not monolithic instruction sets that perform the same calculations every time they are executed. That`s what calculators (and extremely simple programs) do. Instead, they adjust their behavior based on the data provided; external conditions, such as a mouse click or the presence of a device; even under abnormal conditions generated by the program itself. Some programmers prefer the multiline syntax of If. Second, even if it contains a single instruction, because the code is easier to read. Here we specify `M` as input, which checks all case instructions, and if a case matches M, it executes the instruction in the respective case instruction. The If . structure then tests the specified condition and executes the following statements if it is set to True.
The If structure can have a single-line or multiline syntax. To conditionally execute a statement, use single-line syntax as follows: The expression after the While keyword is the second phase, test. Statements in the body are executed until the expression is evaluated at false. Control structures allow you to regulate the flow of program execution. You can use control trees to write Visual Basic code that makes decisions or repeats actions. You can use other control structures to ensure that a resource is deleted, or to execute a series of statements on the same object reference. The diagram above shows that if the Boolean expression (condition) is true, the if statement is executed, and if the Boolean expression is false, the Else code or statement is executed. After that, the control is transferred to the next statement, which occurs immediately after the if-then-else control statement. The expression variable evaluated at the beginning of the statement is the number of the day of the week as reported by the WeekDay() function (a value between 1 and 7).
The value of the expression is then compared to the values that follow each Case keyword. If they match, the instruction block is executed in the next Case keyword and the program moves to the statement that follows the End Select statement. The block of the Case Else statement is optional and executes if none of the preceding Case values match the expression. The If-Then-ElseIf statement allows you to execute a single condition or statement from multiple statements.
