How to build a query

I have to build a query at run-time which will contain a WHERE clause.
There is a field in a table that has to be tested against several values
but I do not know in advance how many values exist. For example,

SELECT fld1, fld2, fld3 FROM tblTable
WHERE fld1 = value[1] OR fld1 = value[2] OR fld1 = value[3]

value[] is an array that contains all of the possible values that fld1 may
take but I do not know how many items such array has. A value of -1 in the
array position indicates that it will not be taken into account. So, I need
to traverse the whole array and include those values different from -1 in
the WHERE clause. I can do a FOR...NEXT and concatenate the conditions
getting only those values different than -1 but I wonder if this is a good
approach; the query might grow depending on the number of valid values in
the array. Please advice if there is a better way to build my query.

Respectfully,
Jorge Maldonado