# In-Program Evaluation

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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.