Alchemy.Core/Extensions/NCalcExtensions.cs

using NCalc;
using System.Text.RegularExpressions;

namespace Alchemy.Core.Extensions
{
    public static class NCalcExtensions
    {
        /// <summary>
        /// 注册自定义函数
        /// </summary>
        /// <param name="expression"></param>
        /// <exception cref="ArgumentException"></exception>
        public static void AddExtraFunction(this Expression expression)
        {
            expression.EvaluateFunction += (name, args) =>
            {
                object paramX = args.Parameters[0].Evaluate();
                double doubleParamX = paramX.ToString().ToDouble();
                object paramY = null;
                double doubleParamY = 0;
                if (args.Parameters.Count() > 1)
                {
                    paramY = args.Parameters[1].Evaluate();
                    doubleParamY = paramY.ToString().ToDouble();
                }
                switch (name.ToLower())
                {
                    // 阶乘函数
                    case "fact":
                        int number = paramX.ToString().ToInt();
                        args.Result = CalculateFactorial(number);
                        break;
                    // 反三角函数（返回弧度）
                    case "sin":
                        args.Result = Math.Sin(paramX.ToString().ToDouble());
                        break;
                    case "cos":
                        args.Result = Math.Cos(paramX.ToString().ToDouble());
                        break;
                    case "tan":
                        args.Result = Math.Tan(paramX.ToString().ToDouble());
                        break;
                    // 反三角函数（返回弧度）
                    case "arcsin":
                    case "asin":
                        if (doubleParamX < -1 || doubleParamX > 1)
                            throw new ArgumentException("反正弦 x∈[-1,1]");
                        args.Result = Math.Asin(paramX.ToString().ToDouble());
                        break;
                    case "arccos":
                    case "acos":
                        if (doubleParamX < -1 || doubleParamX > 1)
                            throw new ArgumentException("反余弦 x∈[-1,1]");
                        args.Result = Math.Acos(paramX.ToString().ToDouble());
                        break;
                    case "arctan":
                    case "atan":
                        args.Result = Math.Atan(paramX.ToString().ToDouble());
                        break;
                    // 角度/弧度转换函数
                    case "rad": // 角度转弧度
                        args.Result = paramX.ToString().ToDouble() * Math.PI / 180;
                        break;
                    //case "deg": // 弧度转角度
                    //    args.Result = Convert.ToDouble(param) * 180 / Math.PI;
                    //    break;
                    // 平方根函数
                    case "sqrt":
                        if (doubleParamX < 0)
                            throw new ArgumentException("平方根 x∈[0,+∞)");
                        args.Result = Math.Sqrt(doubleParamX);
                        break;
                    // 次幂函数
                    case "pow":
                        args.Result = Math.Pow(doubleParamX, doubleParamY);
                        break;
                }
            };
        }
        /// <summary>
        /// 注册常量
        /// </summary>
        /// <param name="expression"></param>
        public static void AddExtraConst(this Expression expression)
        {
            expression.Parameters["e"] = Math.E;    // 自然常数 e
            expression.Parameters["pi"] = Math.PI;  // 圆周率 π
        }
        public static object Evaluate(this string strFormula, string strAngleMode)
        {
            strFormula = Regex.Replace(
                strFormula,
                @"(\d+)\!",
                "fact($1)");
            strFormula = Regex.Replace(
                strFormula,
                @"([^\(\)^]+)\^([^\(\)^]+)",
                "pow($1,$2)");
            if (strAngleMode.Equals("deg"))
            {
                strFormula = Regex.Replace(
                    strFormula,
                    @"(?<!a)r?(sin|cos|tan)(?![a-z])\(([^)]+)\)",
                    "$1(rad($2))");
            }
            strFormula = strFormula.Replace(
                "×",
                "*"
            ).Replace(
                "x",
                "*"
            ).Replace(
                "√",
                "sqrt"
            ).Replace(
                "π",
                "pi"
            ).Replace(
                "%",
                "*0.01"
            );
            Expression expression = new Expression(strFormula);
            expression.AddExtraFunction();
            expression.AddExtraConst();
            string strEvalResult = expression.Evaluate().ToString();
            double doubleResult = strEvalResult.ToDouble();
            double roundedResult = Math.Round(doubleResult, 6);
            return roundedResult;
        }
        private static int CalculateFactorial(int number)
        {
            if (number <= 1) return 1;
            return number * CalculateFactorial(number - 1);
        }
    }
}