桌面计算器C++实现.docx

#include#include#include#includeusing namespace std;enum Token_valueNAME,NUMBER,END,PLUS=+,MINUS=-,MUL=*,DIV=/,PRINT=;,ASSIGN=,LP=(,RP=);Token_value curr_tok = PRINT; double number_value; string string_value; map table;int no_of_errors;double expr(bool get);double term(bool get);double prim(bool get);Token_value get_token();double error(const string& s);/这些声明是必不可少的！Token_value get_token() char ch = 0; cin ch; 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 .: 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; double error(const string& s)no_of_errors+;cerrerror:sn;return 1;double expr(bool get) / add and subtract double left = term(get); for (;) switch (curr_tok) case PLUS: left+=term(true); break; case MINUS: left-=term(true); break; default: return left; / multiply and dividedouble 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/=d; break; return error(divide by 0); default: return left; 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=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();return e;default:return error(primary expected);int main() tablepi = 3.1415926535897932385; tablee = 2.7182818284590452354; cout您将进入计算器模式 endl请输入您要计算的算数表达式并以等号结束endl; while (cin) get_token(); if (curr_tok = END) break; if (curr_tok = PR