一个字符串是0-9 10个数字以 + - * 组合成的，如何计算

Question

比较麻烦,不是一两行代码能完成的,1.
最直接的思路就是使用 栈, (好像数据结构教程都有这个示例吧)2.
这里有个功能比较完善的
http://www.codeproject.com/dotnet/eval3.asp

Answer 1

class Evaluator
        {
            /// <summary>
            /// 梬源宒
            /// </summary>
            /// <param name="Expression"></param>
            /// <returns></returns>
            public static object Eval(string Expression)
            {
                Expression e = new Expression(Expression);
                return e.Result;
            }            /// <summary>
            /// 雄怓晤祒腔源宒, 厒僅怮鞣
            /// </summary>
            /// <param name="expression"></param>
            /// <returns></returns>
            public static object Eval1(string expression)
            {
                CodeDomProvider comp = new CSharpCodeProvider();
                CompilerParameters cp = new CompilerParameters();
                MethodInfo mi;
                StringBuilder codeBuilder = new StringBuilder();                codeBuilder.AppendLine("using System;");
                codeBuilder.AppendLine("using Microsoft.CSharp;");
                codeBuilder.AppendLine("public class Mode");
                codeBuilder.AppendLine("{");
                codeBuilder.AppendLine("    public static object Func()");
                codeBuilder.AppendLine("    {");
                codeBuilder.AppendLine("        try");
                codeBuilder.AppendLine("        {");
                codeBuilder.AppendLine("            return " + (Functions.StrIsEmpty(expression) ? "0" : expression) + ";");
                codeBuilder.AppendLine("        }");
                codeBuilder.AppendLine("        catch");
                codeBuilder.AppendLine("        {");
                codeBuilder.AppendLine("            return \"\";");
                codeBuilder.AppendLine("        }");
                codeBuilder.AppendLine("    }");
                codeBuilder.AppendLine("}");                cp.ReferencedAssemblies.Add("System.dll");
                cp.GenerateExecutable = false;
                cp.GenerateInMemory = true;                string code = codeBuilder.ToString();
                CompilerResults cr = comp.CompileAssemblyFromSource(cp, code);                if (cr.Errors.HasErrors)
                {
                    return null;
                }
                else
                {
                    Assembly a = cr.CompiledAssembly;
                    Type t = a.GetType("Mode");
                    //object mode = a.CreateInstance("Mode");
                    mi = t.GetMethod("Func", BindingFlags.Static | BindingFlags.Public);
                    return mi.Invoke(null, new object[0]);
                }
            }            class Expression
            {
                IList<string> InputLists = new List<string>();
                static IList<string> OperatorList;
                static Expression()
                {
                    OperatorList = new List<string>();
                    OperatorList.Add("+");
                    OperatorList.Add("-");
                    OperatorList.Add("*");
                    OperatorList.Add("/");
                    OperatorList.Add("(");
                    OperatorList.Add(")");
                    OperatorList.Add("#");
                }
                public Expression(string Input)
                {
                    InputLists = new List<string>();
                    Input = Input.Replace(" ", "");
                    string OPNum = "";
                    while (Input.Length > 0)
                    {
                        OPNum = "";
                        while (Char.IsNumber(Input[0]) || Input[0] == '.' || Input[0] == '-')
                        {
                            if (Input[0] == '.' && OPNum == "")
                                break;
                            //判断是负号/减号
                            if (Input[0] == '-')
                            {
                                if (OPNum != "")
                                    break;
                                if (InputLists.Count > 0)
                                {
                                    string Prior = InputLists[InputLists.Count - 1];
                                    if(Prior != "+" && Prior != "-" && Prior != "*" && Prior != "/")
                                        break;
                                }
                            }
                            OPNum += Input[0].ToString();
                            Input = Input.Substring(1);
                            if (Input == "") break;
                        }
                        if (OPNum != "")
                            InputLists.Add(OPNum);
                        if (Input.Length > 0)
                        {
                            InputLists.Add(Input[0].ToString());
                            Input = Input.Substring(1);
                        }
                    }
                    InputLists.Add("#");
                }

Answer 2

Stack<string> OPStack;
                Stack<string> NumStack;
                /// <summary>
                /// 桶湛宒賦彆
                /// </summary>
                public double Result
                {
                    get
                    {
                        OPStack = new Stack<string>();
                        NumStack = new Stack<string>();
                        Position = 0;                        OPStack.Push("#");
                        string Word = ReadNext();
                        while (Word != "#" || OPStack.Peek() != "#")
                        {
                            if (!isOperator(Word))
                            {
                                NumStack.Push(Word);
                                Word = ReadNext();
                                continue;
                            }
                            else
                            {
                                switch (Priority(Word))
                                {
                                    case "<":
                                        OPStack.Push(Word);
                                        Word = ReadNext();
                                        break;
                                    case "=":
                                        OPStack.Pop();
                                        Word = ReadNext();
                                        break;
                                    case ">":
                                        string OP = OPStack.Pop();
                                        double b = Functions.StrToDouble(NumStack.Pop());
                                        double a = Functions.StrToDouble(NumStack.Pop());
                                        NumStack.Push(Operate(a, OP, b));
                                        break;
                                }
                            }                            if (Word == "")
                                break;
                        }
                        return Functions.StrToDouble(NumStack.Pop());
                    }
                }
                string Operate(double a, string OP, double b)
                {
                    double Result = 0;
                    switch (OP)
                    {
                        case "+":
                            Result = a + b;
                            break;
                        case "-":
                            Result = a - b;
                            break;
                        case "*":
                            Result = a * b;
                            break;
                        case "/":
                            Result = a / b;
                            break;
                    }
                    return Result.ToString();
                }
                int Position = 0;
                string ReadNext()
                {
                    if (InputLists.Count > Position)
                    {
                        return InputLists[Position++];
                    }
                    return "";
                }
                bool isOperator(string OP)
                {
                    return OperatorList.Contains(OP);
                }
                string Priority(string OP)
                {
                    string TopOP = OPStack.Peek();
                    switch (TopOP)
                    {
                        case "+":
                        case "-":
                            if (OP == "*" || OP == "/" || OP == "(")
                                return "<";
                            return ">";
                        case "*":
                        case "/":
                            if (OP == "(")
                                return "<";
                            return ">";
                        case "(":
                            if (OP == ")")
                                return "=";
                            if (OP == "#")
                                throw new BusinessLogicException("OP_ERROR");
                            return "<";
                        case ")":
                            return ">";
                        case "#":
                            if (OP == "#")
                                return "=";
                            return "<";
                    }
                    return "";
                }
            }
        }
需要
using System.CodeDom.Compiler;
using System.Reflection;
using Microsoft.CSharp;

Answer 3

function 计算(a as string) as integer
if 有括号 then
replace(括号里的东西,计算(括号里的东西).tostring)
else
if 有乘号 or 有除号
replace('X*X',(X*X).tostring)   '如果第一个是除号就先做除法
else
只有加减法的我就不用说了吧?注意这里是递归出口就行
end if
end if
end function

Answer 4

program exsj_1;
const
  max=100;
var
  number:array[0..max] of integer;
  symbol:array[1..max] of char;
  s,t:string;
  i,p,j,code:integer;
procedure push;{算符入栈运算}
begin
  inc(p);symbol[p]:=s[i];
end;procedure pop;{运算符栈顶元素出栈,并取出操作数栈元素完成相应的运算}
begin
  dec(p);
  case symbol[p+1] of
   '+':inc(number[p],number[p+1]);
   '-':dec(number[p],number[p+1]);
   '*':number[p]:=number[p]*number[p+1];
   '/':number[p]:=number[p] div number[p+1];
  end;
end;function can:boolean;{判断运算符的优先级别,建立标志函数}
begin
  can:=true;
  if (s[i] in ['+','-']) and (symbol[p]<>'(') then exit;
  if (s[i] in ['*','/']) and (symbol[p] in ['*','/']) then exit;
  can:=false;
end;begin
  write('String : '); readln(s); s:='('+s+')'; i:=1; p:=0;
  while i<=length(s) do
    begin
      while s[i]='(' do {左括号处理]
begin
  push; inc(i);
end;
    j:=i;
    repeat {取数入操作数栈}
      inc(i);
    until (s[i]<'0') or (s[i]>'9');
    t:=copy(s,j,i-j); val(t,number[p],code);
    repeat
      if s[i]=')' then {右括号处理} 
begin
  while symbol[p]<>'(' do pop;
  dec(p); number[p]:=number[p+1];
end
      else
begin {根据标志函数值作运算符入栈或出栈运算处理}
  while can do pop;
  push;
end;
inc(i);
    until (i>length(s)) or (s[i-1]<>')');
    end;
  write('Result=',number[0]);
  readln;
end.上面的是用栈的标准算法，我喜欢递归