>e.g. "30, 32, 10, 1000," = 1072

m1 = "30, 32, 10, 1000"
m2 = CHRTRAN(m1,",","+")
? &m2
30+ 32+ 10+ 1000"

>Could you explain how "&" executes the sum ?
>I have used "&" to other things but didn't understand how it works.


It's called macro substitution. What it does is look at the contents of the string as a command, rather than as a string. Some other examples:

k = "thisForm.visible = .f."
&k
* This actually executed the command "thisForm.visible = .f." because that was what k contained
* If it's changed to something else, the same command "&k" executes something else

k = "thisForm.visible = .t."
&k

* In the case of your example, it's like doing this kind of math:
k = "foo = 30 + 20 + 18"
&k
* Right now, foo has been assigned to 68

* And in your explicit example:
k = "30+ 32+ 10+ 1000"
? &k
* It does the operation of the math as though you had typed "? 30+ 32+ 10+ 1000"
* The & tells VFP to do it as a command, rather than data.