Integer.Parse vs. CInt

Basically, I have been using both Integer.Parse and CInt in most of my daily programming tasks, but I'm a little bit confused of what the difference is between the two.

What is the difference between Integer.Parse and CInt in VB.NET?

CInt does a whole lot more than Integer.Parse.

CInt will first check to see if what it was passed is an integer, and then simply casts it and returns it. If it's a double it will try to convert it without first converting the double to a string.

See this from the help for CInt and other Type Conversion Functions

Fractional Parts. When you convert a nonintegral value to an integral type, the integer conversion functions (CByte, CInt, CLng, CSByte, CShort, CUInt, CULng, and CUShort) remove the fractional part and round the value to the closest integer.

If the fractional part is exactly 0.5, the integer conversion functions round it to the nearest even integer. For example, 0.5 rounds to 0, and 1.5 and 2.5 both round to 2. This is sometimes called banker's rounding, and its purpose is to compensate for a bias that could accumulate when adding many such numbers together.

So in short, it does much more than convert a string to an integer, e.g. applying specific rounding rules to fractions, short circuting unecessary conversions etc.

If what you're doing is converting a string to an integer, use Integer.Parse (or Integer.TryParse), if you're coercing an unknown value (e.g. a variant or object from a database) to an integer, use CInt.

Looking with ILDASM at some sample code you can see that CInt is converted to this call:

Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.Conversions::ToInteger(string)

Using .NET Reflector, you can extract this piece of code:

Public Shared Function ToInteger(ByVal Value As String) As Integer
    Dim num As Integer
    If (Value Is Nothing) Then
        Return 0
    End If
    Try
        Dim num2 As Long
        If Utils.IsHexOrOctValue(Value, (num2)) Then
            Return CInt(num2)
        End If
        num = CInt(Math.Round(Conversions.ParseDouble(Value)))
    Catch exception As FormatException
        Throw New InvalidCastException(Utils.GetResourceString("InvalidCast_FromStringTo", New String() { Strings.Left(Value, &H20), "Integer" }), exception)
    End Try
    Return num
End Function

You can see that internally it calls Conversions.ParseDouble.

Therefore, as already explained by Binary Worrier, use Integer.Parse for string coercing and CInt only for casting.