#include <iostream>
#include <map>
#include <string>
#include <cctype>
using namespace std;
enum Token_value {
NAME, NUMBER, END,
PLUS='+', MINUS='-', MUL='*', DIV='/',
PRINT=';', ASSIGN='=', LP='(', RP=')',
};
Token_value curr_tok = PRINT;
map<string,double> table;
double number_value;
string string_value;
int no_of_errors;
double error(const string &s)
{
no_of_errors++;
cerr<<"error: "<<s<<endl;
return 1;
}
Token_value get_token() //取字符
{
char ch;
do {
if(!cin.get(ch)) return curr_tok = END;
}while(ch!='\n' && isspace(ch));
switch(ch) {
case ';':
case '\n':
return curr_tok = PRINT;
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)) {
string_value = ch;
while(cin.get(ch) && isalnum(ch)) string_value += ch;
cin.putback(ch);
return curr_tok = NAME;
}
error("bad token");
return curr_tok = PRINT;
}
}
}
double expr(bool get); //加和减
double prim(bool get) //处理初等项
{
if(get) get_token();
switch(curr_tok) {
case NUMBER:
{
double v = number_value;
get_token();
return v;
}
case NAME:
{
double &v = table[string_value];
if(get_token() == ASSIGN) v = expr(true);
return v;
}
case MINUS:
return -prim(true);
case LP:
{
double e = expr(true);
if(curr_tok!=RP) return error(") expected");
get_token();
return e;
}
default:
return error("primary expected");
}
}
double term(bool get) //乘除
{
double left = prim(get);
for(;;)
switch(curr_tok) {
case MUL:
left *= prim(true);
break;
case DIV:
if(double d = prim(true)) {
left /= d;
break;
}
return error("divide by 0");
default:
return left;
}
}
double expr(bool get) //加减
{
double left = term(get);
for(;;)
switch(curr_tok) {
case PLUS:
left += term(true);
break;
case MINUS:
left -= term(true);
break;
default:
return left;
}
}
int main()
{
table["pi"] = 3.1415926535897932385;
table["e"] = 2.7182818284590452354;
cout<<"please input your string to calculator:"<<endl;
while(cin) {
get_token();
if(curr_tok == END) break;
if(curr_tok == PRINT) continue;
cout<<expr(false)<<endl<<"please input your string to calculator:"<<endl;
}
return no_of_errors;
}
C++计算器例程.rar （13个子文件） 
calculate 
testwork.plg 61KB testwork.cpp 3KB testwork.dsp 4KB testwork.dsw 522B Debug testwork.pch 2.46MB vc60.pdb 172KB vc60.idb 105KB testwork.pdb 1.11MB
testwork.exe 560KB testwork.ilk 811KB testwork.obj 360KB testwork.ncb 49KB testwork.opt 48KB资源评论
yiwushidemingyi2013-01-09对初学者很好的学习资源- XUJIE002012-04-20比较短的代码，可以实现基本功能
- wangwenyan1222013-12-17短小精悍，很好，不过对于输入为英文情况的有点错误~
- leexu20112012-04-17不错的代码，短小精悍，适合初学者
- honghaijie2013-02-05太厉害了 受益匪浅
