C++桌面计算器（第一版）

(此版本为过程式，对应于《The C++ Programming Language 3rd》第六章)

表达式语法分析如下（递归定义）：

 *****************
 * program:
 *     END					//END is end-of-input
 *     expr_list END
 * expr_list:
 *     expression PRINT     // PRINT is semicolon
 *     expression PRINT expr_list
 * expression:
 *     expression + term
 *     expression - term
 *     term
 * term:
 *     term / primary
 *     term * primary
 *     primary
 * primary:
 *     NUMBER
 *     NAME    				// this is variable
 *     NAME = expression
 *     - primary
 *     ( expression ) 
 * *****************

完整文件（不包括Makefile）

• calc.h
• calc.cpp
• main.cpp

calc.h

/**
 * calc.h
 *****************
 * program:
 *     END                  //END is end-of-input
 *     expr_list END
 * expr_list:
 *     expression PRINT     // PRINT is semicolon
 *     expression PRINT expr_list
 * expression:
 *     expression + term
 *     expression - term
 *     term
 * term:
 *     term / primary
 *     term * primary
 *     primary
 * primary:
 *     NUMBER
 *     NAME    				// this is variable
 *     NAME = expression
 *     - primary
 *     ( expression )
 */

#ifndef CALC_H_
#define CALC_H_

#include 
#include 

using namespace std;

enum Token_value {
    NAME,       NUMBER,       END,
    PLUS='+',   MINUS='-',    MUL='*',      DIV='/',
    PRINT=';',  ASSIGN='=',   LP='(',       RP=')'
};

// for DRIVER PROGRAM
extern Token_value curr_tok;
extern map<string, double> table;   // var table
extern int no_of_errors;

extern double expr(bool get);
extern Token_value get_token();
extern double error(const string& s);
// END for DRIVER PROGRAM

extern double term(bool get);
extern double prim(bool get);

#endif

calc.cpp

// calc.cpp
#include "calc.h"

#include 

#include 
#include 
#include 

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

main.cpp

/**
 * main.cpp
 *
 * EAMPLE
 *     ./calc 'rate=1.1934;150/rate;19.75/rate;217/rate'
 */
#include 
#include 

#include "calc.h"

using namespace std;

// --BEGIN-- COMMENT SIMPLE DRIVER
// // DRIVER PROGRAM
// int main(int argc, char **argv) {
//   table["pi"] = 3.1415926535897932385;  // PRE-DEFINED NAMES
//   table["e"]  = 2.7182818284590452354;
//
//   while (cin) {
//       get_token();
//       if (curr_tok == END) break;
//       if (curr_tok == PRINT) continue;
//       cout << expr(false) << endl;
//   }
//
//   return no_of_errors;
// }
// ---END--- COMMENT SIMPLE DRIVER
istream* input;

int main(int argc, char * argv[])
{
    switch (argc) {
        case 1:
            input = &cin;
            break;
        case 2:
            input = new istringstream(argv[1]);
            break;
        default:
            error("too many arguments");
            return 1;
    }

    table["pi"] = 3.1415926535897932385;  // PRE-DEFINED NAMES
    table["e"]  = 2.7182818284590452354;

    while (*input) {
        get_token();
        if (curr_tok == END) break;
        if (curr_tok == PRINT) continue;
        cout << expr(false) << '\n';
    }

    if (input != &cin) delete input;
    return no_of_errors;

}

程序结构如下：