using System;

​

using System.Linq.Expressions;

​

​

​

public class Program

{

    public  static void Main()

    {

        string s = "3*x^2+2/5*x+4";

        Expression<Func<double, double>> expr = MathExpressionGenerator.GetExpression(s);

        Console.WriteLine(expr);

​

        var del = expr.Compile();

​

        Console.WriteLine(del(10));

    }

​

​

}

​

internal static class MathExpressionGenerator

{

    public const string SupportedOps = "+-*/^";

    private static readonly ParameterExpression Parameter = Expression.Parameter(typeof (double), "x");

​

    public static Expression<Func<double, double>> GetExpression(string s)

    {

        ParameterExpression parameterExpression = Expression.Parameter(typeof (double), "x");

        Expression result = GetExpressionInternal(s);

        return Expression.Lambda<Func<double, double>>(result, Parameter);

    }

​

    private static Expression GetExpressionInternal(string s)

    {

        double constant;

        if (s == "x")

            return Parameter;

        if (double.TryParse(s, out constant))

            return Expression.Constant(constant, typeof (double));

        foreach (char op in SupportedOps)

        {

            var split = s.Split(new[] {op}, StringSplitOptions.RemoveEmptyEntries);

            if (split.Length > 1)

            {

                var expression = GetExpressionInternal(split[0]);

                for (int i = 1; i < split.Length; i++)

                {

                    expression = RunOp(expression, GetExpressionInternal(split[i]), op);

                }

                return expression;

            }

        }

        throw new NotImplementedException("never throws");

    }

​

    private static Expression RunOp(Expression a, Expression b, char op)

    {

        switch (op)

        {

            case '+':

                return Expression.Add(a, b);

            case '-':

                return Expression.Subtract(a, b);

            case '/':

                return Expression.Divide(a, b);

            case '*':

                return Expression.Multiply(a, b);

            case '^':

                return Expression.Power(a, b);

        }

        throw new NotSupportedException();

    }

}