C++编程简单的计算器

//输入表达式要完整,例如：输入“2+8=”,然后再按回车键 //本程序只可计算两个多项式之间的四则运算

//输入表达式要完整，例如：输入“2+8=”，然后再按回车键 //本程序只可计算两个多项式之间的四则运算

//date；2012-7

#include <iostream.h>

#include <string>

using namespace std;

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 pide

{ double left = prim(get);

for(;;)

{ switch(curr_tok){

case MUL:

left*=prim(true);

break;

case DIV:

if(double d = prim(true)){ // no zero!!

//输入表达式要完整,例如：输入“2+8=”,然后再按回车键 //本程序只可计算两个多项式之间的四则运算

break;

}

return error("pide 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;

//输入表达式要完整,例如：输入“2+8=”,然后再按回车键 //本程序只可计算两个多项式之间的四则运算

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;

}