Expression evaluator

[Nexinarus]

create a function (which is allowed to use many other functions aswell and subs) that evaluates an expression.

i.e:

print evaluate("2*((3*4)+52)") 'returns 128
print evaluate("-10") 'returns -10
print evaluate("-2^8") 'returns -256
print evaluate("-sin(10+31/5) + 8") 'returns something i cant be bothered calculating :p

try to make it work in all cases, and try to remain as simple as can be.

[Agamemnus]

Something like this, but I can't get it to return back to the same line. I don't know if it's possible.

Code:

DECLARE FUNCTION evaluate# (inputstring$)

CLS
PRINT evaluate("5 + 5")
FUNCTION evaluate# (inputstring$)
OPEN "tempcalc.bas" FOR OUTPUT AS #1
PRINT #1, "a# =" + inputstring$
PRINT #1, "OPEN " + CHR$(34) + "tempcal2.bas" + CHR$(34) + " FOR OUTPUT as #2"
PRINT #1, "PRINT #2, a#"
PRINT #1, "CLOSE"
PRINT #1, "SYSTEM"
CLOSE
CHAIN "tempcalc.bas"
OPEN "tempcal2.bas" FOR INPUT AS #1
INPUT #1, evaluate#
CLOSE
KILL "tempcal2.bas"
KILL "tempcalc.bas"
END FUNCTION

[toonski84]

i once wrote something of the like. it split everything by parthenthesis, then split everything by sign ("+-/*"), went across from left to right, and then replaced the entire parenthesis with the answer and started over until the entire expression was a single numerical value.

your best friend on this one is going to be "instr", and i can hook you up with some good string manipulation routines i wrote if you like.

[Moneo]

TO ALL:
This is not a trivial program. I have a similar program and it takes 700 lines of code to evaluate all the SIN,COS,TAN, etc., plus the AND,OR,XOR and PI.

AGAMEMNUS:

Your idea is brillant! You insert the expression into a generated program which you then chain to in order to do all the work.

I think the CHAIN returns to the top of the calling program. I don't remember exactly, but I think you need to set a switch to know if you are just stating you main program or coming back from the chained program. Work on it.

Maybe instead of the chain, you could generate the subordinate program, then do a shell to compile it. Your main program then shells to execute it. The result cound be in a workfile which the main program then reads and displays.
*****

[Antoni Gual]

The Basic of Sinclair (i think it was Timex in the USA) Spectrum of the 80's had a function VAL$ that EVALUATED EXPRESSIONS. The whole basic interpreter fitted in 16K (and it was slow as hell). It's a function i ever missed...

[Mango]

create a function (which is allowed to use many other functions aswell and subs) that evaluates an expression.

i.e:

print evaluate("2*((3*4)+52)") 'returns 128
print evaluate("-10") 'returns -10
print evaluate("-2^8") 'returns -256
print evaluate("-sin(10+31/5) + 8") 'returns something i cant be bothered calculating :p

try to make it work in all cases, and try to remain as simple as can be.

Why not just use the print function...eg

Code:

CLS
PRINT 2 * ((3 * 4) + 52)
PRINT -10
PRINT -2 ^ 8
PRINT -SIN(10 + 31 / 5) + 8

works just fine for the expressions you posted....

[toonski84]

mango, he's talking about user inputted expressions

[whitetiger0990]

also it wouldn't be much of a good challenge

[Moneo]

MANGO,
Nice try anyway. It's the thought that counts.
*****

[Nexinarus]

LOL. I figured aga's method would come up sooner or later . No really..
Its good but slow heh, and it has to keep calling qb, put it this way, QB has a built in expression evaluator, what this challenge is, is to make your own. It might not be easy but it is a challenge .