Learning VBA: Need Some Explanations on Language

[Agimcomas]

Hi.
I'm new to this forum so let me introduce myself. I am a final year undergraduate in Finance and I'm teaching myself VBA programming to be ready to enter the job market.

I have a copy of "Option Pricing Models & Volatility Using Excel-VBA" and I'm going through the examples in the first chapter.

Let me show you the code:

Function Complexop2 (rP1, iP1, rP2, iP2, operation)
Dim cNum1 As cNum, cNum2 As cNum, cNum3 As cNum
Dim output (2) As Double
cNum1 = setcnum(rP1, iP1)
cnum2 = setcnum(rP2, iP2)
Select Case operation
Case 1: cNum3 = cNumSub(cNum1,cNum2) ' Subtraction
Case 2: cNum3 = cNumProd(cNum1,cNum2) ' Multiplication
Case 3: cNum3 = cNumDiv(cNum1,cNum2) ' Division
End Select
output(1) = cNum3,rP
output(2) = cNum3.iP
complexop2 = output
End Function

I should probably show you one of the previous functions in the program:

]Function Set_cNum (rPart, iPart) As cNum
Set_cNum.rP = rPart
Set_cNum.iP = iPart
End Function

Now, I understand most of the code, but I still don't have a clue on the following:

1. Is cNum a variable type?
2. What does setcnum() mean?
3. What do .rP and .iP mean? What is the syntax?
4. What does the line "complexop2 = output" exactly do?

I hope that somebody can help me out. Thanks in advance!