简单的算数表达式解析器

学习了编译原理的scan和parsing之后写了一个简单的算数表达式解析器，输入为算数表达式，输出结果，支持括号和浮点数运算。
首先画出DFA，根据状态间的转移求出getToken函数。
然后求出EBNF：
<exp> -> <term> { <addop> <term> }
<addop> -> + | -
<term> -> <factor> { <mulop> <factor> }
<mulop> -> *
<factor> -> ( <exp> ) | number
并实现exp、term、factor函数。
源代码：

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
#define BUFLEN 1024
#define MAXTOKENLEN 256
// token的类型
typedef enum
...{
    // 文件结尾
    ENDFILE,
    // 表达式错误
    ERROR, 
    // + - * / ( )符号之一
    SYMBOL,
    // 数字
    NUM,
} TokenType;
// DFA中的状态
typedef enum
...{
    START,    // 开始状态
    INUM,    // 数字的中间状态
    DOT,    // 接受到符号.的状态
    END        // 结束状态
} StateType;
int bufIndex;
char buffer[BUFLEN];                // 缓冲区
char tokenString[MAXTOKENLEN+1];    // 当前token
double exp();
double term();
double factor();
// 获取缓冲区下一个字符
char getNextChar()
...{
    int len = strlen(buffer);
    if(bufIndex < len)
        return buffer[bufIndex++];
    else
        return EOF;
}
// 缓冲区回退一个字符
void ungetNextChar()
...{bufIndex--;}

// 获取缓冲区下一个token，并返回token的类型
TokenType getToken()
...{
    int tokenIndex = 0;
    TokenType currentType;
    StateType state = START;
    bool save;
    while(state != END)
    ...{
        char c = getNextChar();
        save = true;
        switch(state)
        ...{
            case START:
                ...{
                    if(isdigit(c))
                        state = INUM;
                    else if(c == '+' || c == '-' || c == '*' || c == '/' || 
                            c == '(' || c == ')')
                    ...{
                        currentType = SYMBOL;
                        state = END;
                    }
                    else if(c == EOF)
                    ...{
                        currentType = ENDFILE;
                        state = END;
                    }
                    else
                    ...{
                        currentType = ERROR;
                        state = END;
                    }
                    break;
                }
            case INUM:
                ...{
                    if(c == '.')
                        state = DOT;
                    else if(c == EOF)
                    ...{
                        currentType = NUM;
                        state = END;
                    }
                    else if(!isdigit(c))
                    ...{
                        ungetNextChar();
                        save = false;
                        currentType = NUM;
                        state = END;
                    }
                    break;
                }
            case DOT:
                ...{
                    if(isdigit(c))
                        state = INUM;
                    else
                    ...{
                        currentType = ERROR;
                        state = END;
                    }
                    break;
                }
        }
        if(save && tokenIndex < MAXTOKENLEN)
            tokenString[tokenIndex++] = c;
        if(state == END)
            tokenString[tokenIndex] = '/0';
    }
    return currentType;
}
// 输出错误信息
void error()
...{
    printf("syntax error! ");
    exit(1);
}

// parsing中的match函数
void match(const char* expectedToken)
...{
    if(strcmp(expectedToken, tokenString) == 0)
        getToken();
    else
        error();
}
double exp()
...{
    double tmp = term();
    while(tokenString[0] == '+' || tokenString[0] == '-')
    ...{
        switch(tokenString[0])
        ...{
            case '+': 
                   ...{
                       match("+");
                       tmp += term();
                       break;
                   }
            case '-':
                   ...{
                       match("-");
                       tmp -= term();
                       break;
                   }
        }
    }
    return tmp;
}
double term()
...{
    double tmp = factor();
    while(tokenString[0] == '*' || tokenString[0] == '/')
    ...{
        switch(tokenString[0])
        ...{
            case '*':
                   ...{
                       match("*");
                       tmp *= factor();
                       break;
                   }
            case '/':
                   ...{
                       match("/");
                       tmp /= factor();
                       break;
                   }
        }
    }
    return tmp;
}
double factor()
...{
    double tmp;
    if(tokenString[0] == '(')
    ...{
        match("(");
        tmp = exp();
        match(")");
    }
    else if(isdigit(tokenString[0]))
    ...{
        tmp = atof(tokenString);
        getToken();
    }
    else
        error();
    return tmp;
}
int main()
...{
    while(scanf("%s", buffer) != EOF)
    ...{
        bufIndex = 0;
        getToken();
        printf("%s = ", buffer);
        printf("%lf ", exp());
    }
    return 0;
}

运行结果
输入：0.265/(58-6.36*1.25)+3.16-((2.356/69.01)-3.6))
输出：0.265/(58-6.36*1.25)+3.16-((2.356/69.01)-3.6)) = 6.731155