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Nair:

let poweroffourplus2 n =
let n = n * n
let n = n* n

Thank you very much and yes Don also mentioned the same in the same paragraph and I was eager to try to code without reading all the meat. I have one another question, this is realted to funcation thinking what exactly happening to n in the above example

when I use the first let (on the funcation definition) it is coming in as argument value. In the second let, the value of n is pass and creats a new n value (even though Don did mentioned the value of n doesn't change) here it is changing... now the next let uses n, it is using modified n instead of original n........

so how the value 'n' is not changed.??

Thanks again.

This is 'shadowing' - each new 'let n = ...' creates a new variable which hides the old one.  So

let n = n * n

let n = n * n

is like

let n_2 = n_1 * n_1

let n_3 = n_2 * n_2

only they all have the same name.  None of the objects referred to by the name n_i is being mutated.  Instead there are three different objects, and at different points in the code, the name 'n' refers to different ones of those objects.

Thank you very much. I have one more question, I realised if I don't understand this correctly I am going to assume too many things so here is one more

in the following example

let nbynplus5 n =

     let n = n * n

     let n = n + 5

     n;;

In the above example, the let n = n * n will be let n_1 = n * n since it is the first time n is referenced and in the second let, it will be let n_2 = n_1 + 5. Is this correct so if I have make the code it would be

let nbynplus5 n =

     let n_1 = n * n

     let n_2 = n_1 + 5

     n_2;;

Is this correct? also why would be doing instead of using this modified code itself? Is it a style or coding standard?

Thanks again for helping me started.