Full Text Search: The Key to Better Natural Language Queries for NoSQL in Node.js
Date: 1/31/2018 @ 2 p.m. ET
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.
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:
|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|
|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|
|@||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.