C++简单编辑器实例(函数库简单应用).doc

/ OneComputer.cpp : 定义控制台应用程序的入口点。/#include stdafx.h#include iostream#include map#include cctype#include sstream#include stringusing namespace std;istream *input;/double number_value;string string_value; / /初等项函数的变量/maptable;/检查符号表用在prim上面的/int no_of_errors;/double expr(bool get);double term(bool get);double prim(bool get);double error(const string &s);/枚举类型用来表示各种符号enum Token_valueNAME, NUMBER, END,PLUS=+,MINUS=-,MUL=*,DIV=/,PRINT=;,ASSIGN=,LP=(,RP=);Token_value curr_tok=PRINT; /定义字符值，用“；”防止错误导致的致命错误/定义输入函数Token_value get_token()char ch;doif(!cin.get(ch)return curr_tok=END;while(ch!=n&isspace(ch);cinch;switch (ch)case 0:return curr_tok=END;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 .:return curr_tok=NUMBER;default:if(isalpha(ch)string_value=ch;while(cin.get(ch)&isalnum(ch)string_value.push_back(ch);cin.putback(ch);return curr_tok=NAME;error(bad token);return curr_tok=PRINT;int _tmain(int argc, char* argv)switch(argc)case 1:input=&cin;break;case 2:input=new istringstream(argv1);break;default:error(too many arguments);return 1;tablepi=3.141592653547;tablee=2.71818281828478;while(*input)get_token();if(curr_tok=END)break;if(curr_tok=PRINT)continue;coutexpr(false)n;if(input!=&cin) delete input;return no_of_errors;/处理加减的函数double expr(bool get)double left=term(get);for(;)switch(curr_tok)case PLUS:left+=term(true);break;case MINUS:left-=term(true);break;default:return left;/用来处理乘除的函数double term(bool get)double left= prim(get);for(;)switch(curr_tok)case MUL:left*=prim(true);break;case DIV:if(double d=prim(true)left/=prim(true);break;else return error(divide by 0);default:return left;/处理初等项函数double prim(bool get)if(get) get_token();switch(curr_tok)case NUMBER: /浮点常量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) return error() expected!);get_token();retur