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In-Program Evaluation

Posted by Joachim Raidl on September 6th, 1998

In my projects I often need to evaluate expressions. So I created a class that provides evaluation of expressions with the posibility to declare variables and easy functions. For this article I include the XEvaluate-class in a 'calculator'-dialog, but normaly, I use the class in my application like this: XString erg = Evaluate("1+2*sqr(3)").

!!! The XString-class that XEvaluate uses, was also contributed at codeguru.

You can use external variables in a XDoubleMap. This typedef is allready defined in XEvaluate.h (typedef CMap<CString, LPCTSTR, double, double> XDoubleMap;):

	XDoubleMap var;
	var["alpha"] = 10;
	var["beta"] = 20;
	var["test"] = 1.234;

	double erg = dtoa(Evaluate("alpha+beta", var));

It's possible to use userdefined functions with one argument (this argument has to be 'x')

	Evaluate("f:=sin(x)+cos(x)");
	double erg = dtoa(Evaluate("f(pi/2)"));

You can also call Evaluate with more than one expression, if you divide the expressions by a semikolon:

	double erg = dtoa(Evaluate("a=10;b=20;c=a+b");

The following functions and operations are included in XEvaluate:

sin cos tan       trigonometric functions
asin acos atan       inverse trigonometric functions
rad deg gon       trigonometric calculation type
pow sqr sqrt exp log log10 power, square, squareroot, exp, natural log, tenth log
abs int fract fak cube   absolute, integer part, factional part, n!, cube
dec hex bin char     outputtype
fix           set the decimal digits
+ - * /     add, sub, mul, div
% & | ^ ! ~ modulo, binary and, or, xor, not, binary not
< > <= >= == != less, greater, less or equal, greater or equal, equal, not equal
= += -= *= /=   variable setting
@           old value (result of the last calculation)
?           help (lists all functions)
#           reset (delete all functions and variables)
'           actual status (number of decimal digits, trigonometric mode and output mode)
$           var and function list

Use the sample program to find out what's possible with this class.

Download demo project - 47KB

Download source - 8KB

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Comments

  • calculator

    Posted by Legacy on 09/23/2000 12:00am

    Originally posted by: madhuripai

    i want a code on calculator in vc++ using mfc.can i get it
    urgently

    Reply

  • I'd like some update

    Posted by Legacy on 02/17/2000 12:00am

    Originally posted by: LuisR


    Hello,

    This is a great piece of code. Unfortunately, because it is so complex, it has some bugs, some of which have been pointed in here.

    I have one question, does the author have an update for this class that he could send to code guru?? I'd like to use this class in one of my projects, but it still has some bugs.

    See ya,

    -- LuisR

    Reply

  • Shift operator (<<, >>) missing!

    Posted by Legacy on 01/04/2000 12:00am

    Originally posted by: AndreasF

    How can I extend the functionality with the shift operators?
    Please Help me.

    Thanks
    Andreas

    Reply

  • Equality operator bug (and possible fix)

    Posted by Legacy on 07/21/1999 12:00am

    Originally posted by: Thomas Fejes 

    While using this great expression evaluation code,

    I came across a possible bug.  If you run the 

    Calc.exe sample program and enter the following:


    a=5

    b=5

    a==b

    returns 0 instead of 1

    a<=b

    returns 0 instead of 1

    etc.


    also

    c=(a==b)

    does not set c to anything, but a becomes 0


    The cause seems to be that the expressions are 

    calculated before the external variables.  This

    causes the op and txt lists to be added to, but

    the val list never grows, and the comparisons

    always fail.


    A possible fix for this is to reverse the order

    in the XEvaluate.CPP code shown below.  This may

    cause other problems, but it fixes the bug shown

    above.  


    Please comment on other possible remedies.


    before Line 601:


    //====================================================================

    		// Funktionen, Zuweisungen, Variablen, Fehler

    		//====================================================================

    		default:

    			for (name = ""; isalnum(c); c = str[++i]) name += c;

    			i--;

    			// 1. Interne Funktion

    			if (fkt.Lookup(name.Lower(), j))		{ OpPush(STOP); OpPush(j); break; }

    			// 2. Benutzerfunktion

    			if (usrfn.Lookup(name, hilf))			{ TxtPush(name); OpPush(STOP); OpPush(USRFN); break; }

    			// 3. Zuweisung

    			if ((i+1 < len) && (str[i+1] == '='))	{ TxtPush(name); break; }

    			// 4. Arithmetische Zuweisung (+=, ..)

    			if ((i+2 < len) && (str[i+2] == '='))	{ TxtPush(name); break; }

    			// 5. Externe Variable

    			if (extVar && extVar->Lookup(name, a))	{ ValPush(a); break; }

    			// 6. Interne Variable

    			if (var.Lookup(name, a))				{ ValPush(a); break; }

    			// 7. Fehler

    			return Error("var " + name);

    		}


    after:


    //====================================================================

    		// Funktionen, Zuweisungen, Variablen, Fehler

    		//====================================================================

    		default:

    			for (name = ""; isalnum(c); c = str[++i]) name += c;

    			i--;

    			// 1. Interne Funktion

    			if (fkt.Lookup(name.Lower(), j))		{ OpPush(STOP); OpPush(j); break; }

    			// 2. Benutzerfunktion

    			if (usrfn.Lookup(name, hilf))			{ TxtPush(name); OpPush(STOP); OpPush(USRFN); break; }

    			// 5. Externe Variable

    			if (extVar && extVar->Lookup(name, a))	{ ValPush(a); break; }

    			// 6. Interne Variable

    			if (var.Lookup(name, a))				{ ValPush(a); break; }

    			// 3. Zuweisung

    			if ((i+1 < len) && (str[i+1] == '='))	{ TxtPush(name); break; }

    			// 4. Arithmetische Zuweisung (+=, ..)

    			if ((i+2 < len) && (str[i+2] == '='))	{ TxtPush(name); break; }

    			// 7. Fehler

    			return Error("var " + name);

    		}

    Reply

  • Bug&Fix: wrong evaluation of unary functions

    Posted by Legacy on 03/02/1999 12:00am

    Originally posted by: HDaemon 

    int(3*2+0.5) = 6.5 ???


    Fix: str 511

    change

    >    case '(': if (IsBinOp(OpTop())) OpPush(STOP); break;

    to

    >    case '(': if (!IsBinOp(OpTop())) OpPush(STOP); break;

    >		 ~~~

    Reply
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