=====Finding the partial sum of an array=====

//by Richard Russell, July 2015//\\ \\  The **SUM()** function returns the sum of all the elements in a numeric array, and it is much faster than summing the elements yourself in a loop. However you have no control over how many elements are summed: it is always the entire array. To find the sum of the first **n** elements of an array you can use a user-defined function as follows:\\ 
<code bb4w>
        DIM array(999)
        array() = 1
        PRINT FNsum(array(), 500)
</code>
This program prints the value 500, being the sum of the first 500 elements of the array (0 to 499 inclusive). Here is the **FNsum()** function itself:\\ 
<code bb4w>
        DEF FNsum(a(), N%)
        IF DIM(a())<>1 ERROR 0, "Array must be one-dimensional"
        LOCAL !(!^a()+1)
        !(!^a()+1) = N%
        = SUM(a())
</code>