花木兰传奇主题曲歌词:谁有好的计算器程序没有 ?

#include <iostream.h>
#include <string>
using namespace std;

/**************Simple Calculator Code*************************
This program is abstracted from <C++ Programming Language>
all the ideas belong to original author

you can study from it

how to use ?
input a line of expression which is ended with ";"
Examples:
you put :
3+(5+6)*(-1+8);
the reult :
80
and you can continue ...
***********************************************************/
enum Token_value{
NAME, NUMBER, END,
PLUS = '+', MINUS = '-',MUL = '*',DIV = '/',
PRINT = ';',ASSIGN = '=',LP = '(',RP = ')'
};

Token_value curr_tok = PRINT;

// fuction list//////////////////////////////////////
double expr(bool get);
double term(bool get);
double prim(bool get);
Token_value get_token();
double error(const string &s);

//////////////////////////////////////////////////////////
double expr(bool get) //plus and minus
{
double left = term(get);
for(;;)
{
switch(curr_tok){
case PLUS:
left+=term(true);
break;
case MINUS:
left-=term(true);
break;
default:
return left;
}
}
}

double term(bool get) // multiply and divide
{
double left = prim(get);
for(;;)
{
switch(curr_tok){
case MUL:
left*=prim(true);
break;
case DIV:
if(double d = prim(true)){ // no zero!!
left/= d;
break;
}
return error("divide by zero!!\n");
default :
return left;
}
}
}

double number_value;
double string_value;

double prim(bool get)
{
if(get) get_token();

switch(curr_tok){
case NUMBER:
{
double v = number_value;
get_token();
return v;
}
case NAME:
{
double v;
//double &v = table[string_value];
//this table reserved the name mapped with variable
//now we don't use it!
if(get_token()==ASSIGN)
v = expr(true);
return v;
}
case MINUS: // negative
{
return -prim(true);
}
case LP:
{
double e = expr(true);
if(curr_tok!=RP)return error(")expected");
get_token(); // absorb )
return e;
}
default:
return error("primary expected"); // no primary
}
}

Token_value get_token()
{
char ch =0;
cin>>ch;
switch(ch){
case 0:
return curr_tok=END; //return and assignment
case ';':
case '*':
case '/':
case '+':
case '-':
case '(':
case ')':
case '=':
return curr_tok = Token_value(ch);
case '0':case '1':case '2':case '3':case '4':
case '5':case '6':case '7':case '8':case '9':
case '.':
cin.putback(ch);
cin>>number_value;
return curr_tok = NUMBER;
default:
if(isalpha(ch))
{
cin.putback(ch);
cin>>string_value;
return curr_tok = NAME;
}
error("bad token!");
return curr_tok = PRINT;
}
}

int no_of_error;

double error(const string &s)
{
no_of_error++;
cout<<"error:"<<s.data()<<"\n";
return 1;
}

int main()
{
while(cin)
{
get_token();
if(curr_tok==END)break;
if(curr_tok==PRINT) continue;
cout<<expr(false)<<'\n';
}

return no_of_error;
}
不知道为什么，在VC下的汉字在这里是乱码，没办法，程序里我只能用English
程序的主要思想：
利用自顶向下的分析方法:(编译原理）
E= E(+|-)T
T =T(*|/)P
P = i|(E)
不用定义太复杂的数据结构，我是从Bjarne Stroustrup那本书上的代码稍做修改写的这个，给你一个参考。