Well, there are some syntax error with your code, can you try below code, I am sure it may fix the error you are getting.
Module Module1
Sub Main()
Dim a, b, c As Integer
Dim op As String
Console.WriteLine("Calculator")
Console.Write("Enter first number: ")
a = Console.ReadLine() ' Use ReadLine instead of Readline
Console.Write("Enter second number: ")
b = Console.ReadLine() ' Use ReadLine instead of Readline
Console.Write("Enter Operator: ")
op = Console.ReadLine() ' Use ReadLine instead of Readline
If op = "+" Then ' Corrected the operator for addition
c = a + b
ElseIf op = "-" Then
c = a - b
ElseIf op = "*" Then
c = a * b
ElseIf op = "/" Then
If b <> 0 Then
c = a / b
Else
Console.WriteLine("Cannot divide by zero")
Exit Sub ' Exit the program if division by zero is attempted
End If
Else
Console.WriteLine("Invalid operator")
Exit Sub ' Exit the program for invalid operators
End If
Console.WriteLine("Answer = " & c)
End Sub
End Module
Thanks