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Unit 8: Understanding Function and Procedure

It is easier to debug a program, a program with procedures, which breaks a program into discrete
logical limits.
Procedures used in one program can act as building blocks for other programs with slight
modifications.
A Procedure can be Sub, Function or Property Procedure.
Functions are similar to normal procedures but the main purpose of the functions is to accept
certain inputs and pass them on to the main program to finish the execution. They are two types
of function, the built-in functions (or internal functions) and the functions created by the
programmers.
8.1 Function Procedure

Visual Basic has many built-in function. In one respect, function are like miniature programs.
They use input, they process the input, and they have output. Some function we encountered
earlier are listed in Table 8.1
Table 8.1: Some Visual Basic Built-in Function.

Function Example Input Ouput
Int Int(2.6) is 2 number number

Chr Chr(65) is "A" number string

Asc Asc("Apple") is 65 string number

Format Number (12345.628,1) is 12,345.6 number, number string
Although the input can involve several values, the output always consists of a single value. The
items inside the parentheses can be literals (as in Table 5.1), variables, or expressions.
In addition to using built-in function, we can define function of our own. These new function,
called function procedure or user-defined function, are defined in much the same way as Sub
procedure and are used in the same way as built-in function. Like built-in function, function
procedure have a single output that can be of any data type. Function procedure can be used in
expressions in exactly the same way as built-in function. Programs refer to them as if they were
literals, variables, or expressions. function procedure are defined by function blocks of the form
function FunctionName(ByVal var1 As Type1, _
ByVal var2 As Type2, ...) As DataType
statement(s)
Return expression
End function
The variables appearing in the top line are called parameters. Variables declared by statements
inside the function block have local scope. Function names should be suggestive of the role
performed and must conform to the rules for naming variables. The type DataType, which
specifies the type of the output, will be one of String, Integer, Double, and so on. In the preceding
general code, the next-to-last line specifies the output, which must be of type DataType. Like Sub
procedure, function procedure are typed directly into the Code window. (The last line, End
function, will appear automatically after the first line is entered into the Code window.)

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