C++发明者编写的C++计算器源码

#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; }