小型桌面计算器源程序

1、小型桌面计算器源程序#include<iostream>#include<string>#include<map>#include<cctype>using namespace std;map<string,double>table;namespace Lexerenum Token_valueNAME,NUMBER,END,PLUS='+',MINUS='-',MUL='*',DIV='/',PRINT='',ASSIGN='=',LP=

2、'(',RP=')'Token_value curr_tok=PRINT;double number_value;string string_value;Token_value get_token();namespace Errorstruct Zero_divide;struct Syntax_errorconst char* p;Syntax_error(const char* q)p=q;namespace Parserdouble expr(bool get);double term(bool get);double prim(bool get);usi

3、ng namespace Lexer;using namespace Error;namespace Driverint no_of_errors;std:istream*input; void skip();Lexer:Token_value Lexer:get_token() char ch;cin>>ch;switch(ch)case'#':return curr_tok=END;case'':case'*':case'/':case'+':case'-':case'(&#

4、39;: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=

5、NUMBER;default:if(isalpha(ch)cin.putback(ch);cin>>string_value;return curr_tok=NAME;throw Error:Syntax_error("bad token");return curr_tok=PRINT;double Parser:expr(bool get) using namespace Lexer; double left=term(get); for(;) switch(curr_tok) case PLUS: left+=term(true); break; case

6、MINUS: left-=term(true); break; default: return left; double Parser:term(bool get)using namespace Lexer; double left=prim(get); for(;) switch(curr_tok) case MUL: left*=prim(true); break; case DIV: if(double d=prim(true) left/=d; break; throw Error:Zero_divide(); default: return left; double Parser:p

7、rim(bool get) using namespace Lexer;if(get)get_token();switch(curr_tok)case NUMBER:double v=number_value;get_token();return v;case NAME:double& v=tablestring_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) throw Error:Sy

8、ntax_error(")expected");get_token();return e;case END:return 1;default:throw Error:Syntax_error("primary expected");void Driver:skip()no_of_errors+;while(*input) char ch;input->get(ch);switch(ch)case'n':case'':return ;int main(int argc,char*argv)cout<<&qu

9、ot;.欢迎使用桌面计算器."<<endl;cout<<"注意：1.如果输入了一个以字母开头的标识符"cout<<"请在标识符的后面加上一个空格，否则程序将会出错"<<endl;cout<<"2.若输入了一个表达式，切记在后面加上；号"<<endl;cout<<"3.若想退出程序，请输出#"<<endl;Driver:input=&cin; while(*Driver:input) try Lexer:

10、get_token(); if(Lexer:curr_tok=Lexer:END)break; if(Lexer:curr_tok=Lexer:PRINT) continue; cout<<Parser:expr(false)<<endl; catch(Error:Zero_divide) cerr<<"attempt to divide by zero"<<endl; if(Lexer:curr_tok!=Lexer:PRINT) Driver:skip(); catch(Error:Syntax_error e) cerr<<"syntax error:"<<e.p<<endl; if(Lexer:c