>Anybody got any code to convert values back and forth between fractions and decimals?

Let´s suppose you represent decimals as pairs of numbers (NUM, DEN). (I'm using words like "decimals" or "numbers" loosely here. It would be better to talk about "real numbers", "integers", "naturals", and so on.)

To convert a fraction to a decimal, just divide NUM/DEN.

To convert a decimal to a fraction, use something like this:

CLEAR
nORIG = PI() 
nORIG = SQRT(10)

*												
*	Finds a rational (nNUM/nDEN) approximation	
*	to any real number nORIG.					
*												

#DEFINE ZEROES 0.0000000000000000000000000000000

*											
*	Let´s start with an easy approximation.	
*											
nNUM = ROUND(nORIG,0) + ZEROES
nDEN = 1 + ZEROES
N = nORIG - nNUM

DO WHILE .T.
	*											
	*	Print values, and check whether our		
	*	approximation is good enough.			
	*											
	N = nORIG - nNUM/nDEN
	? STR(nNUM,20), STR(nDEN,20), STR(nNUM/nDEN,20,18), STR(nORIG,20,18), STR(N,20,18)
	IF	ABS(N)<1E-20
		EXIT
	ENDIF

	*											
	*	Let's better our approximation. 1/INVN 	
	*	approximates the difference between the	
	*	original number and nNUM/nDEN, so let´s	
	*	add both fractions together.			
	*											
	INVN = ROUND(1/N,0)
	nNUM = nNUM*INVN + nDEN
	nDEN = nDEN*INVN

	*											
	*	Euclid's algorithm; let's scale down	
	*	nNUM, nDEN, so they are mutually prime	
	*											
	A=nNUM
	B=nDEN
	DO WHILE B<>0
		C = MOD(A,B)
		A = B
		B = C
	ENDDO
	nNUM = nNUM/A
	nDEN = nDEN/A
ENDDO

HTH!