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Visual Logic Commands: A Guide to Calling and Reusing Code



A. Visual Logic can do it all... variables, input, assignment, output, conditions, loops, procedures, arrays, files, graphics, debugging, variable watch... everything an instructor needs to teach programming logic and design.


You can also explore the commands available from within the Command Editor. The Command Editor lets you easily enter parameters for each command. This can be accessed by clicking RIGHT and selecting the Command menu structure.




Visual Logic Commands




Logical operators compare Boolean expressions and return a Boolean result. The And, Or, AndAlso, OrElse, and Xor operators are binary because they take two operands, while the Not operator is unary because it takes a single operand. Some of these operators can also perform bitwise logical operations on integral values.


The Not Operator performs logical negation on a Boolean expression. It yields the logical opposite of its operand. If the expression evaluates to True, then Not returns False; if the expression evaluates to False, then Not returns True. The following example illustrates this.


The And Operator performs logical conjunction on two Boolean expressions. If both expressions evaluate to True, then And returns True. If at least one of the expressions evaluates to False, then And returns False.


The Or Operator performs logical disjunction or inclusion on two Boolean expressions. If either expression evaluates to True, or both evaluate to True, then Or returns True. If neither expression evaluates to True, Or returns False.


The Xor Operator performs logical exclusion on two Boolean expressions. If exactly one expression evaluates to True, but not both, Xor returns True. If both expressions evaluate to True or both evaluate to False, Xor returns False.


The AndAlso Operator is very similar to the And operator, in that it also performs logical conjunction on two Boolean expressions. The key difference between the two is that AndAlso exhibits short-circuiting behavior. If the first expression in an AndAlso expression evaluates to False, then the second expression is not evaluated because it cannot alter the final result, and AndAlso returns False.


Similarly, the OrElse Operator performs short-circuiting logical disjunction on two Boolean expressions. If the first expression in an OrElse expression evaluates to True, then the second expression is not evaluated because it cannot alter the final result, and OrElse returns True.


Short-circuiting can improve performance by not evaluating an expression that cannot alter the result of the logical operation. However, if that expression performs additional actions, short-circuiting skips those actions. For example, if the expression includes a call to a Function procedure, that procedure is not called if the expression is short-circuited, and any additional code contained in the Function does not run. Therefore, the function might run only occasionally, and might not be tested correctly. Or the program logic might depend on the code in the Function.


The Visual Logic Command Browser makes it easier for users to browse and add VL code to their simulations by categorizing Visual Logic commands into groups. All the Visual Logic commands are easily viewable at the same time as editing your Visual Logic code and the hover help feature provides a detailed explanation of the commands whilst browsing.


Although you can create, edit, manage, and deploy logic apps in the Azure portal, you can also use Visual Studio when you want to add your logic apps to source control, publish different versions, and create Azure Resource Manager templates for various deployment environments. With Visual Studio Cloud Explorer, you can find and manage your logic apps along with other Azure resources. For example, you can open, download, edit, run, view run history, disable, and enable logic apps that are already deployed in the Azure portal. If you're new to working with Azure Logic Apps in Visual Studio, learn how to create logic apps with Visual Studio.


Deploying or publishing a logic app from Visual Studio overwrites the version of that app in the Azure portal.So if you make changes in the Azure portal that you want to keep, make sure that yourefresh the logic app in Visual Studio from the Azure portal before the next time you deploy or publish from Visual Studio.


Next to the Account Management icon, select Resource Types. Under your Azure subscription, expand Logic Apps so that you can view all the deployed logic apps that are associated with your subscription.


After the logic app opens in Logic Apps Designer, at the bottom of the designer, you can select Code View so that you can review the underlying logic app definition structure. If you want to create a deployment template for the logic app, learn how to download an Azure Resource Manager template for that logic app. Learn more about Resource Manager templates.


You can download logic apps from the Azure portal and save them as Azure Resource Manager templates. You can then locally edit the templates with Visual Studio and customize logic apps for different deployment environments. Downloading logic apps automatically parameterizes their definitions inside Resource Manager templates, which also use JavaScript Object Notation (JSON).


Your logic app definition appears in the resources subsection inside the Resource Manager template. You can now edit the logic app definition and Resource Manager template with Visual Studio. You can also add the template as an Azure Resource Group project to a Visual Studio solution. Learn about Azure Resource Group projects for logic apps in Visual Studio.


To build logic apps for business-to-business (B2B) enterprise integration scenarios, you can link your logic app to a previously created integration account that exists in the same region as your logic app. An integration account contains B2B artifacts, such as trading partners, agreements, schemas, and maps, and lets your logic app use B2B connectors for XML validation and flat file encoding or decoding. Although you can create this link by using the Azure portal, you can also use Visual Studio after meeting the prerequisites, and your logic app exists as a JSON (.json) file inside an Azure Resource Group project. Learn about Azure Resource Group projects for logic apps in Visual Studio.


When you set the Integration Account property in Visual Studio and save your logic app as an Azure Resource Manager template, that template also includes a parameter declaration for the selected integration account. For more information about template parameters and logic apps, see Overview: Automate logic app deployment.


In Visual Studio, if your logic app exists as a JSON (.json) file within an Azure Resource Group project that you use to automate deployment, that logic app is set to a location type and a specific location. This location is either an Azure region or an existing integration service environment (ISE).


To change your logic app's location type or location, you have to open your logic app's workflow definition (.json) file from Solution Explorer by using the Logic App Designer. You can't change these properties by using Cloud Explorer.


Changing the location type from Region toIntegration Service Environmentaffects your logic app's pricing model that's used for billing,limits, integration account support, and so on.Before you select a different location type, make sure that you understand the resulting impact on your logic app.


Make sure that the Logic App Designer has focus by selecting the designer's tab or surface so that the Properties window shows the Choose Location Type and Location properties for your logic app. The project's location type is set to either Region or Integration Service Environment.


When you change the location type or location in Visual Studio and save your logic app as an Azure Resource Manager template, that template also includes parameter declarations for that location type and location. For more information about template parameters and logic apps, see Overview: Automate logic app deployment.


When you open your logic app project in the Logic Apps Designer, you might not get the option for selecting your Azure subscription. Instead, your logic app opens with an Azure subscription that's not the one you want to use. This behavior happens because after you open a logic app's .json file, Visual Studio caches the first selected subscription for future use. To resolve this problem, try one of these steps:


To remove previously selected subscriptions for all logic apps in your solution, delete the hidden Visual Studio settings folder (.vs) in your solution's directory. This location stores your subscription information.


Comparison expressions can be combined using logical operators to produce more complex Boolean expressions. The following example demonstrates the use of comparison operators in conjunction with a logical operator.


The logical operators AndAlso and OrElse exhibit behavior known as short-circuiting. A short-circuiting operator evaluates the left operand first. If the left operand determines the value of the entire expression, then program execution proceeds without evaluating the right expression. The following example illustrates this.


In the preceding example, the operator evaluates the left expression, 45


Similarly, if the left expression in a logical expression using OrElse evaluates to True, execution proceeds to the next line of code without evaluating the right expression, because the left expression has already validated the entire expression. 2ff7e9595c


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