EJERCIOS DE CALCULADORA DE RESISTENCIAS

Continuación este es un ejercicio de VB.NET  para calcular eel valor de las resitencia utilizando formularios:

Aqui estamos ejecutando el formulario con sus respectivos valores

Colocamos un nombre que distingua a cada elemento utilizado en el windows forms

Ahora empezemos:

Public Class Form1
    Private Sub btnreiniciar_Click(sender As Object, e As EventArgs) Handles btnreiniciar.Click

        ComboBox1.Enabled = True
        ComboBox1.ResetText()
        ComboBox2.Enabled = True
        ComboBox2.ResetText()
        ComboBox3.Enabled = True
        ComboBox3.ResetText()
        ComboBox4.Enabled = True
        ComboBox4.ResetText()
        txt1.Text = ""
        Txt2.Text = ""
        txtideal1.Text = ""
        txtideal2.Text = ""
        btn1.BackColor = Nothing
        btn2.BackColor = Nothing
        btn3.BackColor = Nothing
        btn4.BackColor = Nothing

    End Sub

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

        ComboBox2.Enabled = False
        ComboBox3.Enabled = False
        ComboBox4.Enabled = False
        btn1.Enabled = False
        btn2.Enabled = False
        btn3.Enabled = False
        btn4.Enabled = False
    End Sub

    Private Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox1.SelectedIndexChanged
        Select Case ComboBox1.SelectedIndex
            Case 0 : btn1.BackColor = Color.Black
            Case 1 : txt1.Text = "1"
                btn1.BackColor = Color.Maroon
            Case 2 : txt1.Text = "2"
                btn1.BackColor = Color.Red
            Case 3 : txt1.Text = "3"
                btn1.BackColor = Color.Orange
            Case 4 : txt1.Text = "4"
                btn1.BackColor = Color.Yellow
            Case 5 : txt1.Text = "5"
                btn1.BackColor = Color.Green
            Case 6 : txt1.Text = "6"
                btn1.BackColor = Color.Blue
            Case 7 : txt1.Text = "7"
                btn1.BackColor = Color.Violet
            Case 8 : txt1.Text = "8"
                btn1.BackColor = Color.Gray
            Case 9 : txt1.Text = "9"
                btn1.BackColor = Color.White
        End Select
        ComboBox1.Enabled = False
        ComboBox2.Enabled = True
        ComboBox2.Focus()
    End Sub

    Private Sub ComboBox2_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox2.SelectedIndexChanged
        Select Case ComboBox2.SelectedIndex
            Case 0 : btn2.BackColor = Color.Black
            Case 1 : txt1.Text += "1"
                btn2.BackColor = Color.Maroon
            Case 2 : txt1.Text += "2"
                btn2.BackColor = Color.Red
            Case 3 : txt1.Text += "3"
                btn2.BackColor = Color.Orange
            Case 4 : txt1.Text += "4"
                btn2.BackColor = Color.Yellow
            Case 5 : txt1.Text += "5"
                btn2.BackColor = Color.Green
            Case 6 : txt1.Text += "6"
                btn2.BackColor = Color.Blue
            Case 7 : txt1.Text += "7"
                btn2.BackColor = Color.Violet
            Case 8 : txt1.Text += "8"
                btn2.BackColor = Color.Gray
            Case 9 : txt1.Text += "9"
                btn2.BackColor = Color.White

        End Select
        ComboBox2.Enabled = False
        ComboBox3.Enabled = True
        ComboBox3.Focus()
    End Sub

    Private Sub ComboBox3_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox3.SelectedIndexChanged
        Select Case ComboBox3.SelectedIndex
            Case 0
                btn3.BackColor = Color.Black
            Case 1 : txt1.Text += "0  Ω"
                btn3.BackColor = Color.Maroon
            Case 2 : txt1.Text += "00  Ω "
                btn3.BackColor = Color.Red
            Case 3 : txt1.Text += "000  Ω"
                btn3.BackColor = Color.Orange
            Case 4 : txt1.Text += "0000  Ω"
                btn3.BackColor = Color.Yellow
            Case 5 : txt1.Text += "00000  Ω "
                btn3.BackColor = Color.Green
            Case 6 : txt1.Text += "000000  Ω "
                btn3.BackColor = Color.Blue
            Case 7 : txt1.Text += "0000000  Ω "
                btn3.BackColor = Color.Violet
            Case 8 : txt1.Text = txt1.Text * 0.1
                btn3.BackColor = Color.Gray
            Case 9 : txt1.Text = txt1.Text * 0.01
                btn3.BackColor = Color.White

        End Select
        ComboBox3.Enabled = False
        ComboBox4.Enabled = True
    End Sub

    Private Sub ComboBox4_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox4.SelectedIndexChanged

        Select Case ComboBox4.SelectedIndex
            Case 0 : btn4.BackColor = Color.Red
                txt1.Text = txt1.Text
                Txt2.Text = "2"


            Case 1 : btn4.BackColor = Color.Transparent
                txt1.Text = txt1.Text
                Txt2.Text = "0"

            Case 2 : btn4.BackColor = Color.Gold
                txt1.Text = txt1.Text
                Txt2.Text = "5"

            Case 3 : btn4.BackColor = Color.Silver
                txt1.Text = txt1.Text
                Txt2.Text = "10"


        End Select
        ComboBox4.Enabled = False
        ComboBox1.Enabled = True
        ComboBox2.Enabled = True
        ComboBox3.Enabled = True

    End Sub

    Private Sub bntcalcular_Click(sender As Object, e As EventArgs) Handles bntcalcular.Click
        Dim a As Double
        a = (Val(txt1.Text) * Val(Txt2.Text) / 100)
        txtideal1.Text = Val(txt1.Text) - a
        txtideal2.Text = Val(txt1.Text) + a
    End Sub

    Private Sub btnsalir_Click(sender As Object, e As EventArgs) Handles btnsalir.Click
        End
    End Sub
End Class