// calc.cc
#include "calc.h"
#include <ctype.h>
#include <iostream>
#include <map>
#include <string>
using namespace std;
// error function
int no_of_errors;
double error(const string& s)
{
no_of_errors++;
cerr << "error: " << s << '\n';
return 1;
}
// END error function
Token_value curr_tok = PRINT;
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;
}
}
}
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 /= d;
break;
}
return error("divide by 0");
default:
return left;
}
}
}
double number_value;
string string_value;
map<string, double> table; // var table
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 = 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");
}
}
// --BEGIN-- OPTIMIZE get_token function
Token_value get_token()
{
char ch = 0;
cin >> ch;
switch (ch) {
case 0:
return curr_tok = end; // assign and return
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;
}
}
Token_value get_token()
{
char ch = 0;
// --BEGIN-- ignore blanks except '\n'
// do {
// if (!cin.get(ch)) return curr_tok = END;
// } while (ch != '\n' && isspace(ch));
cin >> ch;
// ---END--- ignore blanks except '\n'
switch (ch) {
case 0:
return curr_tok = END; // assign and return
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)) {
// --BEGIN-- Optimize to avoid meeting blank issue
// cin.putback(ch);
// cin >> string_value;
string_value = ch;
while (cin.get(ch) && isalnum(ch)) string_value.push_back(ch);
cin.putback(ch);
// ---END_-- Optimize to avoid meeting blank issue
return curr_tok = NAME;
}
error("bad token");
return curr_tok = PRINT;
}
}
// ---END--- OPTIMIZE get_token function
experiment_three.rar （17个子文件） 
experiment_three 
calc.cpp 3KB experiment_three.vcxproj 7KB experiment_three.vcxproj.filters 1KB main.cpp 1KB calc.h 1KB Debug vc140.pdb 492KB experiment_three.tlog CL.write.1.tlog 2KB CL.read.1.tlog 20KB unsuccessfulbuild 0B CL.command.1.tlog 1KB link.write.1.tlog 722B link.command.1.tlog 1KB link.read.1.tlog 3KB experiment_three.lastbuildstate 230B main.obj 485KB experiment_three.log 2KB vc140.idb 507KB资源评论
