Purpose In this project, a database management system will be implemented to make the self-ordering easier. The users for this program will be used for customers in various restaurants. It will take a customer’s order, total it, and give them an amount. The system will instruct the customer to enter the correct amount. If the amount is not enough, the system will instruct them to enter more money. If it is too less, however, the system will them issue out change. Use of Visual Basics Visual Basic for Applications (ABA) will be used because it is a programming language built right into many Microsoft programs.
This language is built on the Basic programming language made popular by PC’s over the past 25 years. ABA shares similarities with other Windows implementations of the Basic language, such as Visual Basic. If you are familiar with programming in a different language (including using macros), you can quickly get up to speed with ABA. There are a few terms you should know before you start programming in ABA: Procedure. A section of programming coder designed to accomplish a specific task, which your program statements can use throughout your program.
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There are two types of procedures: functions and fibrousness. Function. A procedure that returns a value after it completes its task. When called, functions typically appear on the right side of an equal sign in an expression. Subroutine. A procedure that does not return a value after it completes its task. Module. A named collection of procedures. You typically attach modules to specific forms or reports. You can accomplish many tasks simply by using macros. This implies–and correctly so–that not everyone needs to use ABA.
As a general rule, if you can accomplish a task by using macros, do so. Macros are simpler to implement and easier to maintain. However, there are certain tasks which you cannot do with macros or which you can better implement through ABA You should use ABA instead of macros when you: Want to create your own functions. Need to handle events that pass parameters or accept return values. Need to perform error handling. Need to process information on a record-by-record basis. Want your application to run as quickly as possible.
There are other instances when you should use ABA, as well: When you don’t want to manually create or manipulate database objects. If you want to create a library. If you are writing your own Wizards. When you need to perform system-level operations such as ODE and OLE. When you want to access Windows API functions or DEL files for other applications. Parts of a Program In ABA, a program consists of procedures. These procedures are made up of individual program lines, which you must put together according to ABA rules.
These rules are referred to as syntax. There are many elements that go into a program, including the following: Statements Variables Operators Functions Database objects and collections Understanding Variables Your ABA programs use variables to store information. Just like you can store data in a field within a table, you can store information in a variable for use in a program. Variables are so named because their contents can vary, meaning your program can change their values. Variables can be very powerful.
They let you create general-purpose routines that can act and make decisions based on the value within the variable. For example, consider the following logical sentence: If the temperature is high enough, I will go to the beach. In this instance, the temperature is the variable. If it is high enough, you will do something; if not, you will not. Variables serve the same purpose in a program. Later in this chapter, you will learn how ABA uses variables to make decisions within your programs. Data Types When you define a table, you need to define what type of information will be stored in each field of the table.
String type variables can contain any characters–letters, numbers, or symbols?which you can think of. The Date data type is not really a date, as you might expect. For instance, humans represent a date such as June 11, 1999. ABA, however, works with date serial numbers. These are a numeric representation of a date, in the form of a number. The appearance of that number (for instance, June 1 1, 1999) is the format of the number, not the date serial number itself. Access uses the special Date data type to contain serial numbers which represent any date between January 1, 100 and December 31 , 9999.
Another interesting data type is Object. This data type is actually a reference to an object tracked by Access. Many of the actions you perform in ABA are upon objects, such as tables, forms, reports, and the pieces thereof. Each of these are objects, and can be addressed within ABA. Later in this chapter you will learn more about ABA objects in Access. The last ABA data type is not purported directly in setting data types for fields. The Variant data type automatically adapts to the type of information it contains. If you store a number in a variant, it behaves like a numeric data type.
If you store characters in it, it behaves like a string. In addition, you can store special values in a variant, such as dates and times. There are nine types of data you can store in variants: Empty Null Integer Long Single Double Currency Date string Most of these types of data should look familiar by now. The first two, however, may not. A variant is empty if your program has never assigned it a value. Typically, a variant is empty at the beginning of your program, before you ever use it. A variant is Null if your program has initialized it but it currently contains no data.
Declaring Variables Before you can use a variable within your program, you need to declare it. This simply means that you need to let ABA know what name you are going to use for the variable and what data type it will store. There are two ways you can declare a variable–either implicitly or explicitly. Implicit declaration means you simply start using the variable. For example, if ABA encounters the following line in your program, and you have never used the variable “LLC” before, then ABA assumes you want to define a variable by the name of “LLC”.
ICC = 123. 456 Because you are assigning a single precision value to the variable, you have implied the variable’s type as single. Explicit declaration means you declare the variable before actually using it. You explicitly declare using one of the following declaration statements: Dim. Dimensions (sets aside space for) a variable. You can access the variable within the current procedure only. Each mime your program uses the procedure, ABA reinitialized the variable. Global. Same as Dim, except the variable is accessible in any procedure. Static.
Same as Dim, except ABA does not reinitialize the variable every time the procedure is used. Assigning Values to Variables To inform ABA that a particular variable should contain a particular value, you need to assign the value to the variable. To assign a value to a variable, use the assignment operator (the equal sign) in an equation, as shown here: Dim SSL As Integer SSL = 65 After you program this assignment, you can use the variable “SSL” anywhere else in your program and ABA will understand you actually mean the number 65. Understanding Operators An operator is a symbol that informs ABA about the operation you want to perform.
For instance, the expression 2 + 2 uses an operator–the plus sign. There are 4 general categories of ABA operators: Math operators. Used to put together mathematical equations. Examples include addition, subtraction, multiplication, and division. Comparison operators. Used to determine how two Operands relate to each other. The result Of a comparison operation is always either True or False. String operators. Seed to combine the characters in strings. Logical operators. Used to test conditions. Examples include AND, OR, and NOT. The result of a logical operation is always either True or False.
There are 20 different operators spread among these 4 categories: Operator Category Meaning + Math Addition Math / Math Operator Subtraction Multiplication Division Exponentiation Category Math Meaning Integer division Mod Math Mood lulus Comparison Equal Comparison Greater than Comparison Greater than or equal Comparison Not equal & String Concatenation AND Logical And Q.V. Logical Equivalent IMP Logical Implication NOT Logical Not (or the logical opposite of) OR Logical or XEROX Logical Exclusive Or Understanding Functions Technically, a function is a procedure that returns a value.
ABA has a wide variety of built-in functions which you can use in your programs. These functions are important because they keep you from having to “reinvent the wheel” for common tasks. There are many, many functions built into ABA. These functions are categorized by the type of work they do. The categories are: Math Functions Financial Functions Data Conversion Functions String Functions Date and Time Functions Transcendental Functions Miscellaneous Functions creating a ABA Module Now that you know how to put together a program, you are ready to give it a try.
TO create a ABA procedure, you follow many of the same Steps you follow when you created macros. The general steps in ABA programming are as follows: 1. Identify the task you want to accomplish. 2. Plan the steps needed to accomplish that task. 3. Create the programming code necessary to implement the steps. 4. Test the program. 5. Refine the program. 6. Repeat steps 4 and 5 until the program works correctly. You create ABA programming code by using the ABA Editor, which is described in the following section. What is the ABA Editor? You create ABA programs using the ABA Editor.
To start the ABA Editor, first click your mouse on the Modules button in the Database window. Then, click your mouse on the New button. Access, in turn, displays the ABA Editor. Notice that there are several different parts to the ABA Editor. In the upper left corner is what the editor refers to as the Project window. This is where you can see the different elements of your project and any modules that have been defined in the workbook. Just below the Project window is the Properties window. Here you can specify different attributes of whatever you have selected in the Project window.
For most simple development needs, you will never do much with the Properties window. To the right of the Properties window, and at the very bottom of the screen, is the Immediate window. This is where you can either test parts of your procedures during development or you can find the immediate results of various commands. The Immediate window comes in very handy during testing and debugging, when they are necessary. The Module window, which is the largest window n the screen, is where you do your programming. At the top of the Module window are two drop-down lists. The one on the left is called the Object box.
The one on the right is the Procedure box. You use the Object box to select which object you want to work with. When you first create a module, the object is set to the word General, meaning you are working on a general module, not on one associated with a particular object in a form or report. The Procedure box is where you indicate the name of the procedure on which you want to work. If you choose or specify a different procedure in this box, he information Access shows in the Module window changes to reflect the ABA statements you have assigned to that procedure.
The top level of a module is the Declarations section. It begins with the procedure name you indicate in the Procedure box when you first create a module. Take a look at the Module window. It contains the programming code already defined for the declarations section. To enter programming statements into a procedure, you type them in the Module window. As you enter information, Access checks to make sure it can understand what you type. In other words, Access checks the syntax of what you enter. You use the correct syntax when you follow the ABA rules of grammar.
You can cut, copy, and paste sections of code using standard Windows mouse Or keyboard techniques. You can perform these operations either in the same procedure or between different procedures. Creating a New Procedure Assume for a moment that you want to create a procedure that will step through the records in the Business Customers table, which you developed earlier in this book. The procedure will check the ZIP Code of every record. If the ZIP Code equals a specific value, the procedure will change the records salesperson. Your first step is to create a new procedure in the Module window.
To do this, you must first decide if your procedure will be a subroutine or a function. Your choice will depend on the task you want the procedure to perform. Remember, if you want your procedure to return a value, you need to make it a function. You also need to determine a name for your procedure. Unlike the names you use for fields, tables, and other database objects, this procedure name cannot contain spaces. In this case, let’s say you decide to use the name Changeableness’s, which is quite descriptive Specifying Parameters
Take a look at the parentheses after the function name (on the first line of the procedure). Inside these parenthesis, you specify arguments (parameters) for your function. Position the cursor between the parentheses, and change the line so it looks like this: Function Changeability’s(Captained As String Newsreels As Long) This statement tells ABA that your function requires two arguments: Captained and Newswire. The first parameter is a string, and the second is a long integer. Your function will use these arguments to determine which records to change and what to change them to.
There is one other hint you need to do to this function’s first line. You already know that you use functions when you want to return information to whoever called it. In this case, you want to return the number of records the function changes. You need to specify, on this first line, what type of value your function will return. Add As Long to the end of the line, so it looks like this: Function Changeableness’s(Captained As String, Newswire As Long) As Long The As Long tells ABA that this function returns a long integer to the calling routine.
With these declarations out of the way, you are ready to enter the body of our routine in between the first and last lines on your screen. Saving Your Module After you have finished your first procedure, you can create other procedures in this same module, if you desire. Thinness, your next step is to save your module and close it. You save the module by clicking your mouse on the Save tool on the toolbar, or by choosing Save from the File menu. Access then asks you for the name you want to use for your module. Enter a name, such as Module, and then press ENTER or click your mouse on K.
Access will save the module as a part of the database. Now you can close your module by clicking your mouse on the Close icon (the X) in the upper-right corner of the ABA Editor program window. Testing Your Procedure Once you have created a procedure, you need to test it out. ABA provides several different tools you can use to do this. These tools include: The Immediate window Debug-Print Breakpoints Using the Immediate Window Perhaps the most important tool you can use to test your procedures is the Immediate window.
This window lets you see the results of your procedures right away. Using the window, you can uncover problems before they get ride among dozens of different procedures you may develop. For example, you can test your functions to see what values they are returning. Remember that the Immediate window appears at the bottom of the ABA Editor workspace. (If it is not visible for some reason, you can display it by choosing Immediate Window from the View menu. ) You can select the window by clicking your mouse in the window.
Access displays a cursor and then waits for your command. You can switch to another ABA Editor window by simply clicking the mouse in the desired window. Later, you can hop back to the Immediate window by clicking your mouse within it. You should note that before a procedure is executed, the value of all variables is undefined, meaning you cannot print them. In addition, after a procedure is executed, ABA wipes out the contents of all variables. This means that the only time you can meaningfully print the value assigned to a variable is while a procedure is executing.
Typically, this is done after a breakpoint is reached, as discussed shortly. Using Debug. Print Another way you can use the Immediate window is with Debug. Print. ABA lets you use Debug. Print to display the contents of any variable, as your program nuns. Using Debug-Print, you can watch closely a variable’s value to see how your code changes the variable. By tracking a variable’s value in this way, you may detect errors in your code. To display a variable value in this way, you include Debug. Print in a line of code.
For example, if you want to determine the value of the Tempore variable, you can use the following line of code: Debug. Print “Value of Tempore is ” & Tempore If Tempore contains a value of 4, when ABA executes this line, Access will display the following in the Immediate window: Value of Tempore is 4 Debug. Print has no other effect on your program; everything else remains the same. Debug. Print is particularly useful when you’re debugging, since you don’t have to bother with stopping and restarting your program.
Setting Breakpoints Another testing tool which ABA provides for you is a breakpoint–a place you specify within your program where you want the program’s execution to stop. Once your program stops, you can use the Immediate window to display information about variables or to test out other procedures, if you desire. ABA lets you set breakpoints on any line of code in your program or within any procedure Of your program. TO set a breakpoint, position the cursor on the program line where you want ABA to stop.
Then, select the Toggle Breakpoint option from the Debug menu or click your mouse on the toolbar Breakpoint tool. When you later run the program and ABA encounters the line at which you have set the breakpoint, ABA will do three things: Pause Display your program (with the line containing the breakpoint) in the program window. Wait for your command. Normally, you set breakpoints so you can inspect the status of the program while it is executing. This is the time when you can print out the contents of rabbles, as discussed earlier in this chapter.
You can also use other ABA menu commands (those under the the Debug menu) to step through your procedure one instruction at a time. If you are done inspecting the program, you can also choose the Run command from the Run menu. This causes the procedure to continue executing as if no breakpoint had been encountered. To later remove a breakpoint, stop your program and position the cursor on the line that contains the breakpoint. Then, perform any of the actions you used to first set the breakpoint: select the Toggle Breakpoint option from the Debug menu or click your mouse on the toolbar Breakpoint tool.