Mathematical expression in string: Alternatives to NCalc

Question

I need to read from file mathematical expression and evaluate it's value. Example expression formats are as follow:

• "5" - constant
• "3.1415 * 0.25" - constant expressions
• "{0} - 50" - expressions with value placeholders (String.Format())
• "Abs({0} - 50)" - just like up but with mathematical functions

I was using so far NCalc which worked great until it had to deal with expressions like follow:

• "3.0 * Abs({0} + 34)"

Unfortunately in example just above the result of following code:

var value = ReadValueFromSomewhere(); // Lets say it returns 125.75
var exprStr = ReadExpression(); // returns: "3.0 * Abs({0} + 34)"
var toEval = String.Format(exprStr, value);
var result = new NCCalc.Expression(toEval).Evaluate()

is following exception:

System.InvalidOperationException

Operator '*' can't be applied to operands of types 'double' and 'decimal' NCalc.Numbers.Multiply(object, object) NCalc.Domain.EvaluationVisitor.Visit(NCalc.Domain.BinaryExpression) NCalc.Domain.BinaryExpression.Accept(NCalc.Domain.LogicalExpressionVisitor) NCalc.Expression.Evaluate()

It seems like Abs() method returns decimal and NCalc can't handle doing calculations between double and decimal (propably bug?). So I would like to ask what alternative libraries I could use instead of NCalc? Or perhaps there is other workaround than expression:

• "Abs(3.0) * Abs({0} + 34)"

?

Answer 1

What do you mean by "expressions with value placeholders"? Can you give more specific example? You can try mXparser - it works for Java and .NET.

Example of usage:

Expression e = new Expression("3.1415 * 0.25");
double v = e.calculate();

Follow mXparser tutorial.

Regards