Tag Archives: Calculations

Simple Calculator (why would we need an another one!?)

Hi everyone! This is a simple calculator which programmed by me on Visual studio. Worked out on .NET 2.0 framework and used Visual Basic as the programming language. This calculator is absolutely looks like (and also the functionality) the windows calculator on accessories menu.

CaptureCalcThe code block for button click events is as below.

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'2010-08-14 Calculator Solution By Rasan
Public Class frmMain
    Dim lastbtn As String = "oprt"
    Dim lastoprt As String
    Dim result As Double = 0
    Dim ram As Double = 0
    Dim mplus As Double = 0
    Dim num As Integer
    Dim isdec As Boolean = False
    Dim upperval As Double = 0
    Dim lowerval As Double = 0
 
    Private Sub btn1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn1.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "1")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "1")
            End If
            lastbtn = "in"
        End If
    End Sub
 
    Private Sub btn2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn2.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "2")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "2")
            End If
            lastbtn = "in"
        End If
    End Sub
 
    Private Sub btn3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn3.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "3")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "3")
            End If
            lastbtn = "in"
        End If
    End Sub
 
    Private Sub btn4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn4.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "4")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "4")
            End If
            lastbtn = "in"
        End If
    End Sub
 
    Private Sub btn5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn5.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "5")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "5")
            End If
            lastbtn = "in"
        End If
    End Sub
 
    Private Sub btn6_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn6.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "6")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "6")
            End If
            lastbtn = "in"
        End If
    End Sub
 
    Private Sub btn7_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn7.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "7")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "7")
            End If
            lastbtn = "in"
        End If
    End Sub
 
    Private Sub btn8_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn8.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "8")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "8")
            End If
            lastbtn = "in"
        End If
    End Sub
 
    Private Sub btn9_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn9.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "9")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "9")
            End If
            lastbtn = "in"
        End If
    End Sub
 
    Private Sub btn0_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn0.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                If txtDisplay.Text <> "0." Then
                    num = txtDisplay.Text.Length - 1
                    txtDisplay.Text = txtDisplay.Text.Insert(num, "0")
                End If
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "0")
            End If
            lastbtn = "in"
        End If
    End Sub
 
    Private Sub btnDot_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDot.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Then
                txtDisplay.Text = "0."
            End If
            isdec = True
            lastbtn = "in"
        End If
    End Sub
 
    Private Sub btnPlus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPlus.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastoprt <> "plus" Or lastbtn = "in" Then
                ram = txtDisplay.Text
                If lastoprt = "eq" Then
                    result = txtDisplay.Text
                End If
                If lastbtn <> "oprt" Then
                    If lastoprt = "plus" Then
                        result = result + ram
                    ElseIf lastoprt = "minus" Then
                        result = result - ram
                    ElseIf lastoprt = "mul" Then
                        result = result * ram
                    ElseIf lastoprt = "dev" Then
                        result = result / ram
                    Else
                        result = result + ram
                    End If
                End If
                lastbtn = "oprt"
                lastoprt = "plus"
                txtDisplay.Text = result
                If txtDisplay.Text.Contains(".") Then
                    txtDisplay.Text = result
                Else
                    txtDisplay.Text = result & "."
                End If
                isdec = False
            End If
        End If
    End Sub
 
    Private Sub btnMinus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnMinus.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastoprt <> "minus" Or lastbtn = "in" Then
                ram = txtDisplay.Text
                If lastoprt = "eq" Then
                    result = txtDisplay.Text
                End If
                If lastbtn <> "oprt" Then
                    If lastoprt = "plus" Then
                        result = result + ram
                    ElseIf lastoprt = "minus" Then
                        result = result - ram
                    ElseIf lastoprt = "mul" Then
                        result = result * ram
                    ElseIf lastoprt = "dev" Then
                        result = result / ram
                    Else
                        result = result + ram
                    End If
                End If
                lastbtn = "oprt"
                lastoprt = "minus"
                txtDisplay.Text = result
                If txtDisplay.Text.Contains(".") Then
                    txtDisplay.Text = result
                Else
                    txtDisplay.Text = result & "."
                End If
                isdec = False
            End If
        End If
    End Sub
 
    Private Sub btnMul_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnMul.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastoprt <> "mul" Or lastbtn = "in" Then
                ram = txtDisplay.Text
                If lastoprt = "eq" Then
                    result = txtDisplay.Text
                End If
                If lastbtn <> "oprt" Then
                    If lastoprt = "plus" Then
                        result = result + ram
                    ElseIf lastoprt = "minus" Then
                        result = result - ram
                    ElseIf lastoprt = "mul" Then
                        result = result * ram
                    ElseIf lastoprt = "dev" Then
                        result = result / ram
                    Else
                        result = result + ram
                    End If
                End If
                lastbtn = "oprt"
                lastoprt = "mul"
                txtDisplay.Text = result
                If txtDisplay.Text.Contains(".") Then
                    txtDisplay.Text = result
                Else
                    txtDisplay.Text = result & "."
                End If
                isdec = False
            End If
        End If
    End Sub
 
    Private Sub btnDev_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDev.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastoprt <> "dev" Or lastbtn = "in" Then
                ram = txtDisplay.Text
                upperval = ram
                If lastoprt = "eq" Then
                    result = txtDisplay.Text
                End If
                If lastbtn <> "oprt" Then
                    If lastoprt = "plus" Then
                        result = result + ram
                    ElseIf lastoprt = "minus" Then
                        result = result - ram
                    ElseIf lastoprt = "mul" Then
                        result = result * ram
                    ElseIf lastoprt = "dev" Then
                        result = result / ram
                    Else
                        result = result + ram
                    End If
                End If
                lastbtn = "oprt"
                lastoprt = "dev"
                txtDisplay.Text = result
                If txtDisplay.Text.Contains(".") Then
                    txtDisplay.Text = result
                Else
                    txtDisplay.Text = result & "."
                End If
                isdec = False
            End If
        End If
    End Sub
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        txtDisplay.Text = "0."
    End Sub
 
    Private Sub btnEq_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnEq.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            ram = txtDisplay.Text
            If lastoprt = "plus" Then
                result = result + ram
            ElseIf lastoprt = "minus" Then
                result = result - ram
            ElseIf lastoprt = "mul" Then
                result = result * ram
            ElseIf lastoprt = "dev" Then
                result = result / ram
            Else
                result = ram
            End If
            lastbtn = "oprt"
            lastoprt = "eq"
            txtDisplay.Text = result
            If txtDisplay.Text.Contains(".") Then
                txtDisplay.Text = result
            Else
                txtDisplay.Text = result & "."
            End If
            isdec = False
        End If
    End Sub
 
    Private Sub btnNeg_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNeg.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            ram = txtDisplay.Text
            If ram <> 0 Then
                If txtDisplay.Text.Contains("-") Then
                    txtDisplay.Text = txtDisplay.Text.Remove(0, 1)
                Else
                    txtDisplay.Text = txtDisplay.Text.Insert(0, "-")
                End If
            End If
        End If
    End Sub
 
    Private Sub btnC_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnC.Click
        txtDisplay.Text = "0."
        lastbtn = "oprt"
        lastoprt = ""
        isdec = False
        result = 0
        ram = 0
        mplus = 0
        lowerval = 0
        upperval = 0
        lblDisplay.Text = ""
    End Sub
 
    Private Sub btnCe_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCe.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            result = 0
            ram = 0
        End If
        txtDisplay.Text = "0."
        lastbtn = "oprt"
        isdec = False
    End Sub
 
    Private Sub btnBack_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnBack.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Or lastbtn <> "in" Then
            Beep()
        Else
            num = txtDisplay.Text.Length
            If txtDisplay.Text.Chars(num - 1) = "." Then
                If isdec = True Then
                    isdec = False
                Else
                    txtDisplay.Text = txtDisplay.Text.Remove(num - 2, 1)
                End If
            Else
                txtDisplay.Text = txtDisplay.Text.Remove(num - 1, 1)
            End If
            If num = 2 Or (txtDisplay.Text.Contains("-") And num = 3) Then
                txtDisplay.Text = "0."
                isdec = False
                lastbtn = "oprt"
            End If
        End If
    End Sub
 
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnMplus.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            ram = txtDisplay.Text
            mplus = mplus + ram
            lblDisplay.Text = "M"
        End If
        lastbtn = "oprt"
    End Sub
 
    Private Sub btnSqrt_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSqrt.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            Dim sqrt As Double = 0
            ram = txtDisplay.Text
            lastbtn = "sqrt"
            lastoprt = "sqrt"
            sqrt = ram ^ (1 / 2)
            txtDisplay.Text = sqrt
            If txtDisplay.Text.Contains(".") Then
                txtDisplay.Text = sqrt
            Else
                txtDisplay.Text = sqrt & "."
            End If
            isdec = False
        End If
    End Sub
 
    Private Sub btnMminus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnMminus.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            mplus = 0
            lblDisplay.Text = ""
        End If
        lastbtn = "oprt"
    End Sub
 
    Private Sub btnMr_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnMr.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            txtDisplay.Text = mplus
            If txtDisplay.Text.Contains(".") Then
                txtDisplay.Text = mplus
            Else
                txtDisplay.Text = mplus & "."
            End If
        End If
        lastbtn = "oprt"
    End Sub
 
    Private Sub btnUndreone_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnUndreone.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            Dim undrone As Double = 0
            ram = txtDisplay.Text
            lastbtn = "sqrt"
            lastoprt = "sqrt"
            undrone = 1 / ram
            txtDisplay.Text = undrone
            If txtDisplay.Text.Contains(".") Then
                txtDisplay.Text = undrone
            Else
                txtDisplay.Text = undrone & "."
            End If
            isdec = False
        End If
    End Sub
 
    Private Sub btnMs_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnMs.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            mplus = txtDisplay.Text
            lblDisplay.Text = "M"
        End If
        lastbtn = "oprt"
    End Sub
 
    Private Sub btnPercentage_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPercentage.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            lowerval = txtDisplay.Text
            If lowerval = 0 Then
                result = 0
            Else
                result = upperval / lowerval * 100
            End If
            txtDisplay.Text = result
            If txtDisplay.Text.Contains(".") Then
                txtDisplay.Text = result
            Else
                txtDisplay.Text = result & "."
            End If
            lastbtn = "oprt"
        End If
    End Sub
 
    Private Sub ExitToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ExitToolStripMenuItem.Click
        End
    End Sub
 
    Private Sub AboutToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles AboutToolStripMenuItem.Click
        frmAbout.Show()
    End Sub
End Class
'2010-08-14 Calculator Solution By Rasan
Public Class frmMain
    Dim lastbtn As String = "oprt"
    Dim lastoprt As String
    Dim result As Double = 0
    Dim ram As Double = 0
    Dim mplus As Double = 0
    Dim num As Integer
    Dim isdec As Boolean = False
    Dim upperval As Double = 0
    Dim lowerval As Double = 0

    Private Sub btn1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn1.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "1")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "1")
            End If
            lastbtn = "in"
        End If
    End Sub

    Private Sub btn2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn2.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "2")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "2")
            End If
            lastbtn = "in"
        End If
    End Sub

    Private Sub btn3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn3.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "3")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "3")
            End If
            lastbtn = "in"
        End If
    End Sub

    Private Sub btn4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn4.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "4")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "4")
            End If
            lastbtn = "in"
        End If
    End Sub

    Private Sub btn5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn5.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "5")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "5")
            End If
            lastbtn = "in"
        End If
    End Sub

    Private Sub btn6_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn6.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "6")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "6")
            End If
            lastbtn = "in"
        End If
    End Sub

    Private Sub btn7_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn7.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "7")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "7")
            End If
            lastbtn = "in"
        End If
    End Sub

    Private Sub btn8_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn8.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "8")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "8")
            End If
            lastbtn = "in"
        End If
    End Sub

    Private Sub btn9_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn9.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                num = txtDisplay.Text.Length - 1
                txtDisplay.Text = txtDisplay.Text.Insert(num, "9")
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "9")
            End If
            lastbtn = "in"
        End If
    End Sub

    Private Sub btn0_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn0.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Or txtDisplay.Text = "0." Then
                txtDisplay.Text = "."
            End If
            If isdec = False Then
                If txtDisplay.Text <> "0." Then
                    num = txtDisplay.Text.Length - 1
                    txtDisplay.Text = txtDisplay.Text.Insert(num, "0")
                End If
            Else
                If txtDisplay.Text = "." Then
                    txtDisplay.Text = "0."
                End If
                num = txtDisplay.Text.Length
                txtDisplay.Text = txtDisplay.Text.Insert(num, "0")
            End If
            lastbtn = "in"
        End If
    End Sub

    Private Sub btnDot_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDot.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastbtn = "oprt" Or lastbtn = "sqrt" Then
                txtDisplay.Text = "0."
            End If
            isdec = True
            lastbtn = "in"
        End If
    End Sub

    Private Sub btnPlus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPlus.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastoprt <> "plus" Or lastbtn = "in" Then
                ram = txtDisplay.Text
                If lastoprt = "eq" Then
                    result = txtDisplay.Text
                End If
                If lastbtn <> "oprt" Then
                    If lastoprt = "plus" Then
                        result = result + ram
                    ElseIf lastoprt = "minus" Then
                        result = result - ram
                    ElseIf lastoprt = "mul" Then
                        result = result * ram
                    ElseIf lastoprt = "dev" Then
                        result = result / ram
                    Else
                        result = result + ram
                    End If
                End If
                lastbtn = "oprt"
                lastoprt = "plus"
                txtDisplay.Text = result
                If txtDisplay.Text.Contains(".") Then
                    txtDisplay.Text = result
                Else
                    txtDisplay.Text = result & "."
                End If
                isdec = False
            End If
        End If
    End Sub

    Private Sub btnMinus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnMinus.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastoprt <> "minus" Or lastbtn = "in" Then
                ram = txtDisplay.Text
                If lastoprt = "eq" Then
                    result = txtDisplay.Text
                End If
                If lastbtn <> "oprt" Then
                    If lastoprt = "plus" Then
                        result = result + ram
                    ElseIf lastoprt = "minus" Then
                        result = result - ram
                    ElseIf lastoprt = "mul" Then
                        result = result * ram
                    ElseIf lastoprt = "dev" Then
                        result = result / ram
                    Else
                        result = result + ram
                    End If
                End If
                lastbtn = "oprt"
                lastoprt = "minus"
                txtDisplay.Text = result
                If txtDisplay.Text.Contains(".") Then
                    txtDisplay.Text = result
                Else
                    txtDisplay.Text = result & "."
                End If
                isdec = False
            End If
        End If
    End Sub

    Private Sub btnMul_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnMul.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastoprt <> "mul" Or lastbtn = "in" Then
                ram = txtDisplay.Text
                If lastoprt = "eq" Then
                    result = txtDisplay.Text
                End If
                If lastbtn <> "oprt" Then
                    If lastoprt = "plus" Then
                        result = result + ram
                    ElseIf lastoprt = "minus" Then
                        result = result - ram
                    ElseIf lastoprt = "mul" Then
                        result = result * ram
                    ElseIf lastoprt = "dev" Then
                        result = result / ram
                    Else
                        result = result + ram
                    End If
                End If
                lastbtn = "oprt"
                lastoprt = "mul"
                txtDisplay.Text = result
                If txtDisplay.Text.Contains(".") Then
                    txtDisplay.Text = result
                Else
                    txtDisplay.Text = result & "."
                End If
                isdec = False
            End If
        End If
    End Sub

    Private Sub btnDev_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDev.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            If lastoprt <> "dev" Or lastbtn = "in" Then
                ram = txtDisplay.Text
                upperval = ram
                If lastoprt = "eq" Then
                    result = txtDisplay.Text
                End If
                If lastbtn <> "oprt" Then
                    If lastoprt = "plus" Then
                        result = result + ram
                    ElseIf lastoprt = "minus" Then
                        result = result - ram
                    ElseIf lastoprt = "mul" Then
                        result = result * ram
                    ElseIf lastoprt = "dev" Then
                        result = result / ram
                    Else
                        result = result + ram
                    End If
                End If
                lastbtn = "oprt"
                lastoprt = "dev"
                txtDisplay.Text = result
                If txtDisplay.Text.Contains(".") Then
                    txtDisplay.Text = result
                Else
                    txtDisplay.Text = result & "."
                End If
                isdec = False
            End If
        End If
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        txtDisplay.Text = "0."
    End Sub

    Private Sub btnEq_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnEq.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            ram = txtDisplay.Text
            If lastoprt = "plus" Then
                result = result + ram
            ElseIf lastoprt = "minus" Then
                result = result - ram
            ElseIf lastoprt = "mul" Then
                result = result * ram
            ElseIf lastoprt = "dev" Then
                result = result / ram
            Else
                result = ram
            End If
            lastbtn = "oprt"
            lastoprt = "eq"
            txtDisplay.Text = result
            If txtDisplay.Text.Contains(".") Then
                txtDisplay.Text = result
            Else
                txtDisplay.Text = result & "."
            End If
            isdec = False
        End If
    End Sub

    Private Sub btnNeg_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNeg.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            ram = txtDisplay.Text
            If ram <> 0 Then
                If txtDisplay.Text.Contains("-") Then
                    txtDisplay.Text = txtDisplay.Text.Remove(0, 1)
                Else
                    txtDisplay.Text = txtDisplay.Text.Insert(0, "-")
                End If
            End If
        End If
    End Sub

    Private Sub btnC_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnC.Click
        txtDisplay.Text = "0."
        lastbtn = "oprt"
        lastoprt = ""
        isdec = False
        result = 0
        ram = 0
        mplus = 0
        lowerval = 0
        upperval = 0
        lblDisplay.Text = ""
    End Sub

    Private Sub btnCe_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCe.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            result = 0
            ram = 0
        End If
        txtDisplay.Text = "0."
        lastbtn = "oprt"
        isdec = False
    End Sub

    Private Sub btnBack_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnBack.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Or lastbtn <> "in" Then
            Beep()
        Else
            num = txtDisplay.Text.Length
            If txtDisplay.Text.Chars(num - 1) = "." Then
                If isdec = True Then
                    isdec = False
                Else
                    txtDisplay.Text = txtDisplay.Text.Remove(num - 2, 1)
                End If
            Else
                txtDisplay.Text = txtDisplay.Text.Remove(num - 1, 1)
            End If
            If num = 2 Or (txtDisplay.Text.Contains("-") And num = 3) Then
                txtDisplay.Text = "0."
                isdec = False
                lastbtn = "oprt"
            End If
        End If
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnMplus.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            ram = txtDisplay.Text
            mplus = mplus + ram
            lblDisplay.Text = "M"
        End If
        lastbtn = "oprt"
    End Sub

    Private Sub btnSqrt_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSqrt.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            Dim sqrt As Double = 0
            ram = txtDisplay.Text
            lastbtn = "sqrt"
            lastoprt = "sqrt"
            sqrt = ram ^ (1 / 2)
            txtDisplay.Text = sqrt
            If txtDisplay.Text.Contains(".") Then
                txtDisplay.Text = sqrt
            Else
                txtDisplay.Text = sqrt & "."
            End If
            isdec = False
        End If
    End Sub

    Private Sub btnMminus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnMminus.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            mplus = 0
            lblDisplay.Text = ""
        End If
        lastbtn = "oprt"
    End Sub

    Private Sub btnMr_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnMr.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            txtDisplay.Text = mplus
            If txtDisplay.Text.Contains(".") Then
                txtDisplay.Text = mplus
            Else
                txtDisplay.Text = mplus & "."
            End If
        End If
        lastbtn = "oprt"
    End Sub

    Private Sub btnUndreone_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnUndreone.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            Dim undrone As Double = 0
            ram = txtDisplay.Text
            lastbtn = "sqrt"
            lastoprt = "sqrt"
            undrone = 1 / ram
            txtDisplay.Text = undrone
            If txtDisplay.Text.Contains(".") Then
                txtDisplay.Text = undrone
            Else
                txtDisplay.Text = undrone & "."
            End If
            isdec = False
        End If
    End Sub

    Private Sub btnMs_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnMs.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            mplus = txtDisplay.Text
            lblDisplay.Text = "M"
        End If
        lastbtn = "oprt"
    End Sub

    Private Sub btnPercentage_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPercentage.Click
        If txtDisplay.Text.Contains("Infinity.") Or txtDisplay.Text.Contains("NaN.") Then
            Beep()
        Else
            lowerval = txtDisplay.Text
            If lowerval = 0 Then
                result = 0
            Else
                result = upperval / lowerval * 100
            End If
            txtDisplay.Text = result
            If txtDisplay.Text.Contains(".") Then
                txtDisplay.Text = result
            Else
                txtDisplay.Text = result & "."
            End If
            lastbtn = "oprt"
        End If
    End Sub

    Private Sub ExitToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ExitToolStripMenuItem.Click
        End
    End Sub

    Private Sub AboutToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles AboutToolStripMenuItem.Click
        frmAbout.Show()
    End Sub
End Class

How does it looks? OK. just feel free to download the source code from the below link, study it and improve it.

Download: Calculator VS Project