Question

I’ve just started with VB in VS2010 and attempting to write a simple console calculator. However, i can’t get it to wait to display the output. The console window closes immediately even after putting a Console.Read(). I guess the input buffer from my ReadLine() still has some valid characters. I’ll paste the code here:

Sub Main()

    Dim num1 As Double
    Dim num2 As Double
    Dim op As Char
    Dim ans As Double

    Console.Write("Enter first number:")

    num1 = CType(Console.ReadLine(), Double)

    Console.Write("Enter second number:")
    num2 = CType(Console.ReadLine(), Double)

    Console.Write("Enter an operator:")
    op = ChrW(Console.Read())

    Select Case op
        Case "+"
            ans = num1 + num2
            Console.WriteLine("Result=" + ans.ToString())

        Case "-"
            ans = num1 - num2
            Console.WriteLine("Result=" + ans.ToString())


        Case "*"
            ans = num1 * num2
            Console.WriteLine("Result=" + ans.ToString())

        Case "/"
            If num2 <> 0 Then
                ans = num1 / num2
                Console.WriteLine("Result=" + ans.ToString())
            Else : Console.WriteLine("Error: Division by zero")
            End If

    End Select

    Console.Read()

End Sub

I’ve noticed that i need to put 3 Console.Read()’s at the end of the code to finally get the console to wait. Why is this happening?

Answer 1

Try adding this to the end and you’ll see what’s happening:

Console.WriteLine(Console.Read().ToString())
Console.WriteLine(Console.Read().ToString())
Console.Read()

The Console.Read for op is unblocked when you hit return, but the carriage return/line feed sequence is in the buffer and hasn’t been consumed. So two additional Console.Read calls clear the CR (Dec: 13)/LF (Dec: 10) and then the third blocks like you want.

Console.ReadLine doesn’t work because it consumes the CR/LF and there’s nothing then to block existing the app. Two Console.ReadLine calls or Console.ReadLine followed by Console.Read would work.