Optional arguments are supported in C# too

var res1 = Microsoft.VisualBasic.Strings.InStr("Abc", "b", Microsoft.VisualBasic.CompareMethod.Binary);
var res2 = Microsoft.VisualBasic.Strings.InStr("Abc", "b");
var str1 = Microsoft.VisualBasic.Strings.Replace("adc", "d", "b", 1, -1, Microsoft.VisualBasic.CompareMethod.Text);
var str2 = Microsoft.VisualBasic.Strings.Replace("adc", "d", "b");