Computer Programming Concepts and Visual Basic David I. Schneider

92 Computer Programming Concepts and Visual Basic
Object Property Setting
frm4_3_5 Caption Ceil Function
lblNumber Caption Enter a number
txtNumber Text (blank)
cmdCalculate Caption Calculate Ceil
picResults
Private Function Ceil(x As Single) As Single
‘Round nonintegers up
Ceil = -Int(-x)
End Function
Private Sub cmdCalculate_Click()
‘Demonstrate the Ceil function
picResults.Print “Ceil(“; txtNumber.Text; “) =”; Ceil(Val(txtNumber.Text))
txtNumber.Text = “”
txtNumber.SetFocus
End Sub
[Run, type 4.3 into the text box, click the command button, type 4 into the text box, and then click the
command button again.]
There are many reasons for employing user-defined functions.
1. User-defined functions are consistent with the modular approach to program
design. Once we realize a particular function is needed, we can give it a name
but save the task of figuring out the computational details until later.
2. Sometimes a single formula must be used several times in a program. Specifying
the formula as a function saves repeated typing of the same formula,
improves readability, and simplifies debugging.
3. Functions written for one program can be used in other programs. Programmers
maintain a collection, or library, of functions that might be needed.
COMMENTS
1. By default, variables passed to a Function procedure are passed by reference;
that is, their values are subject to being changed by the Function procedure.
Variables also can be passed by value to Function procedures and thereby have
their values persist. As with Sub procedures, a variable is passed by value if the
variable is enclosed in an extra pair of parentheses when the function is
invoked, or if the corresponding parameter in the Private Function statement is