1 Public Class Form1
  2 	Inherits System.Windows.Forms.Form
  3 
  4 	' This application calculates a student's grade point average (GPA).
  5 	' It demonstrates how to use Function procedures.
  6 
  7 	Dim defaultTextboxColor As Color
  8 
  9 	Private Sub Form1_Load(ByVal sender As System.Object, _
 10 		ByVal e As System.EventArgs) Handles MyBase.Load
 11 
 12 		'Get the default text box color.
 13 		defaultTextboxColor = txtCreditHours1.BackColor
 14 	End Sub
 15 
 16 
 17 	Private Sub btnCalculate_Click(ByVal sender As System.Object, _
 18 		ByVal e As System.EventArgs) Handles btnCalculate.Click
 19 
 20 		' This event procedure displays the quality points for
 21 		' each course and the GPA.
 22 		Dim intGradePoints As Integer
 23 		Dim sngGradePointAvg As Single
 24 
 25 		' Display the quality points for course 1.
 26 		intGradePoints = CalcGradePoints(txtGrade1.Text)
 27 		lblGradePoints1.Text = intGradePoints.ToString()
 28 
 29 		' Display the quality points for course 2.
 30 		intGradePoints = CalcGradePoints(txtGrade2.Text)
 31 		lblGradePoints2.Text = intGradePoints.ToString()
 32 
 33 		' Display the quality points for course 3.
 34 		intGradePoints = CalcGradePoints(txtGrade3.Text)
 35 		lblGradePoints3.Text = intGradePoints.ToString()
 36 
 37 		' Display the quality points for course 4.
 38 		intGradePoints = CalcGradePoints(txtGrade4.Text)
 39 		lblGradePoints4.Text = intGradePoints.ToString()
 40 
 41 		' Get the grade point average and display 
 42 		' it with 2 decimal places.
 43 		sngGradePointAvg = CalcGPA()
 44 		lblGPA.Text = FormatNumber(sngGradePointAvg, 2)
 45 
 46 	End Sub
 47 
 48 
 49 	Function CalcGradePoints(ByVal strGrade As String) As Integer
 50 
 51 		' This function accepts a letter grade as an argument
 52 		' and returns the number of grade points for that grade.
 53 
 54 		Dim intPoints As Integer
 55 
 56 		Select Case strGrade.ToUpper()
 57 			Case "A"
 58 				intPoints = 4
 59 			Case "B"
 60 				intPoints = 3
 61 			Case "C"
 62 				intPoints = 2
 63 			Case "D"
 64 				intPoints = 1
 65 			Case "F"
 66 				intPoints = 0
 67 		End Select
 68 
 69 		' Return the number of grade points.
 70 		Return intPoints
 71 	End Function
 72 
 73 	Function CalcGPA() As Single
 74 
 75 		' This function calculates and returns the student's 
 76 		' Grade Point Average (GPA).
 77 
 78 		' Get the total credit hours.
 79         Dim intTotalCreditHours As Integer = _
 80          CInt(txtCreditHours1.Text) + _
 81          CInt(txtCreditHours2.Text) + _
 82          CInt(txtCreditHours3.Text) + _
 83          CInt(txtCreditHours4.Text)
 84 
 85 		' Calculate the total quality points.
 86 		Dim intTotalQualityPoints As Integer = _
 87 		   (CInt(txtCreditHours1.Text) * CInt(lblGradePoints1.Text)) + _
 88 		   (CInt(txtCreditHours2.Text) * CInt(lblGradePoints2.Text)) + _
 89 		   (CInt(txtCreditHours3.Text) * CInt(lblGradePoints3.Text)) + _
 90 		   (CInt(txtCreditHours4.Text) * CInt(lblGradePoints4.Text))
 91 
 92 		' Divide the total quality points by the total credit
 93 		' hours, producing the grade point average.
 94 		Return CSng(intTotalQualityPoints / intTotalCreditHours)
 95 	End Function
 96 
 97 	Function ValidateHours(ByVal tbox As TextBox) As Boolean
 98 
 99 		' Return True if the text box contains a valid integer. 
100 		' If not, display an error message, change the TextBox color,
101 		' and return False.
102 
103 		If IsNumeric(tbox.Text) Then
104 			tbox.BackColor = defaultTextboxColor
105 			Return True
106 		Else
107 			lblMessage.Text = "Invalid Credit Hours. Please enter an integer"
108 			tbox.BackColor = Color.Aqua
109 			Return False
110 		End If
111 	End Function
112 
113 	Private Sub txtCreditHours1_Validating(ByVal sender As Object, _
114 		ByVal e As System.ComponentModel.CancelEventArgs) _
115 		Handles txtCreditHours1.Validating
116 
117 		If ValidateHours(txtCreditHours1) Then
118 			e.Cancel = False
119 		Else
120 			e.Cancel = True
121 		End If
122 	End Sub
123 
124 	Private Sub txtCreditHours2_Validating(ByVal sender As Object, _
125 		ByVal e As System.ComponentModel.CancelEventArgs) _
126 		Handles txtCreditHours2.Validating
127 
128 		If ValidateHours(txtCreditHours2) Then
129 			e.Cancel = False
130 		Else
131 			e.Cancel = True
132 		End If
133 	End Sub
134 
135 	Private Sub txtCreditHours3_Validating(ByVal sender As Object, _
136 		ByVal e As System.ComponentModel.CancelEventArgs) _
137 		Handles txtCreditHours3.Validating
138 
139 		If ValidateHours(txtCreditHours3) Then
140 			e.Cancel = False
141 		Else
142 			e.Cancel = True
143 		End If
144 	End Sub
145 
146 	Private Sub txtCreditHours4_Validating(ByVal sender As Object, _
147 		ByVal e As System.ComponentModel.CancelEventArgs) _
148 		Handles txtCreditHours4.Validating
149 
150 		If ValidateHours(txtCreditHours4) Then
151 			e.Cancel = False
152 		Else
153 			e.Cancel = True
154 		End If
155 	End Sub
156 
157 
158 	Function ValidateGrade(ByVal tbox As TextBox) As Boolean
159 
160 		' Return True if the text box contains a valid grade letter
161 		' (A,B,C,D, or F). If not, display an error message, change 
162 		' the TextBox color, and return False.
163 
164 		Dim grade As String = tbox.Text.ToUpper()
165 
166 		If grade = "A" Or grade = "B" Or grade = "C" Or grade = "D" _
167 			Or grade = "F" Then
168 			tbox.BackColor = defaultTextboxColor
169 			Return True
170 		Else
171 			lblMessage.Text = "Invalid Grade. Please enter A, B, C, D or F"
172 			tbox.BackColor = Color.Aqua
173 			Return False
174 		End If
175 
176 	End Function
177 
178 	Private Sub txtGrade1_Validating(ByVal sender As Object, _
179 		ByVal e As System.ComponentModel.CancelEventArgs) _
180 		Handles txtGrade1.Validating
181 
182 		If ValidateGrade(txtGrade1) Then
183 			e.Cancel = False
184 		Else
185 			e.Cancel = True
186 		End If
187 	End Sub
188 
189 	Private Sub txtGrade2_Validating(ByVal sender As Object, _
190 		ByVal e As System.ComponentModel.CancelEventArgs) _
191 		Handles txtGrade2.Validating
192 
193 		If ValidateGrade(txtGrade2) Then
194 			e.Cancel = False
195 		Else
196 			e.Cancel = True
197 		End If
198 	End Sub
199 
200 	Private Sub txtGrade3_Validating(ByVal sender As Object, _
201 		ByVal e As System.ComponentModel.CancelEventArgs) _
202 		Handles txtGrade3.Validating
203 
204 		If ValidateGrade(txtGrade3) Then
205 			e.Cancel = False
206 		Else
207 			e.Cancel = True
208 		End If
209 	End Sub
210 
211 	Private Sub txtGrade4_Validating(ByVal sender As Object, _
212 		ByVal e As System.ComponentModel.CancelEventArgs) _
213 		Handles txtGrade4.Validating
214 
215 		If ValidateGrade(txtGrade4) Then
216 			e.Cancel = False
217 		Else
218 			e.Cancel = True
219 		End If
220 	End Sub
221 
222 	Private Sub btnClear_Click(ByVal sender As System.Object, _
223 	 ByVal e As System.EventArgs) Handles btnClear.Click
224 
225 		' Clear the text boxes
226 		txtGrade1.Clear()
227 		txtGrade2.Clear()
228 		txtGrade3.Clear()
229 		txtGrade4.Clear()
230 		txtCreditHours1.Clear()
231 		txtCreditHours2.Clear()
232 		txtCreditHours3.Clear()
233 		txtCreditHours4.Clear()
234 		' Clear the labels
235 		lblGradePoints1.Text = ""
236 		lblGradePoints2.Text = ""
237 		lblGradePoints3.Text = ""
238 		lblGradePoints4.Text = ""
239 		lblGPA.Text = ""
240 	End Sub
241 
242 	Private Sub btnExit_Click(ByVal sender As System.Object, _
243 		ByVal e As System.EventArgs) Handles btnExit.Click
244 
245 		' End the application
246 		Me.Close()
247 	End Sub
248 
249 End Class