>For those who know about asymptotic behavior:
>
>Given an array of increasing numbers and a number X, create a linear algorithm that finds whether the array contains two numbers that sum to X (and those two numbers if they exist).
>
>Daniel


How about

LPARAMETER nFind

LOCAL nFront, nBack, nSum

DIMENSION a[10]
a[1]= 3
a[2]= 5
a[3]= 7
a[4]= 9
a[5]= 10
a[6]= 12
a[7]= 14
a[8]= 16 
a[9]= 18 
a[10]= 20

nFront= 1
nBack= ALEN(a)

nSum= a[nFront] + a[nBack]
DO WHILE nSum != nFind AND nFront != nBack
	IF nSum > nFind
		nBack = nBack - 1
	ENDIF
	IF nSum < nFind
		nFront= nFront + 1
	ENDIF
	nSum= a[nFront] + a[nBack]
ENDDO

IF nFront != nBack
	? a[nFront], a[nBack]
ELSE
	? "Not Found"
ENDIF

Keep a pointer to the front, and one to the back, If the sunm is greater, move the back pointer in one, if the sum is less move the front pointer in one.