四则运算表达式

功能：计算四则运算表达式，支持括号，加减乘除，负数

代码如下：

//#token.h#
#ifndef TOKEN_H_INCLUDED
#define TOKEN_H_INCLUDED

typedef enum {
    BAD_TOKEN,
    NUMBER_TOKEN,
    ADD_OPERATOR_TOKEN,
    SUB_OPERATOR_TOKEN,
    MUL_OPERATOR_TOKEN,
    DIV_OPERATOR_TOKEN,
    LEFT_PAREN_TOKEN,
    RIGHT_PAREN_TOKEN,
    END_OF_LINE_TOKEN
} TokenKind;

#define MAX_TOKEN_SIZE (100)

typedef struct {
    TokenKind kind;
    double      value;
    char        str[MAX_TOKEN_SIZE];
} Token;

void set_line(char *line);
void get_token(Token *token);

#endif /* TOKEN_H_INCLUDED */

//#parser.c#
#include <stdio.h>
#include <stdlib.h>
#include "token.h"

#define LINE_BUF_SIZE (1024)

static Token st_look_ahead_token;
static int st_look_ahead_token_exists;

static void
my_get_token(Token *token) {
    if (st_look_ahead_token_exists) {
        *token = st_look_ahead_token;
        st_look_ahead_token_exists = 0;
    } else {
        get_token(token);
    }
}

static void
unget_token(Token *token) {
    st_look_ahead_token = *token;
    st_look_ahead_token_exists = 1;
}

double parse_expression(void);

static double
parse_primary_expression() {
    Token token;
    double value = 0.0;
    int minus_flag = 0;

    my_get_token(&token);
    if (token.kind == SUB_OPERATOR_TOKEN) {
        minus_flag = 1;
    } else {
        unget_token(&token);
    }

    my_get_token(&token);
    if (token.kind == NUMBER_TOKEN) {
        value = token.value;
    } else if (token.kind == LEFT_PAREN_TOKEN) {
        value = parse_expression();
        my_get_token(&token);
        if (token.kind != RIGHT_PAREN_TOKEN) {
            fprintf(stderr, "missing ')' error.
");
            exit(1);
        }
    } else {
        unget_token(&token);
    }
    if (minus_flag) {
        value = -value;
    }
    return value;
}

static double
parse_term() {
    double v1;
    double v2;
    Token token;

    v1 = parse_primary_expression();
    for (;;) {
        my_get_token(&token);
        if (token.kind != MUL_OPERATOR_TOKEN
            && token.kind != DIV_OPERATOR_TOKEN) {
            unget_token(&token);
            break;
        }
        v2 = parse_primary_expression();
        if (token.kind == MUL_OPERATOR_TOKEN) {
            v1 *= v2;
        } else if (token.kind == DIV_OPERATOR_TOKEN) {
            v1 /= v2;
        }
    }
    return v1;
}

double
parse_expression() {
    double v1;
    double v2;
    Token token;


    v1 = parse_term();
    for (;;) {
        my_get_token(&token);
        if (token.kind != ADD_OPERATOR_TOKEN
            && token.kind != SUB_OPERATOR_TOKEN) {
            unget_token(&token);
            break;
        }
        v2 = parse_term();
        if (token.kind == ADD_OPERATOR_TOKEN) {
            v1 += v2;
        } else if (token.kind == SUB_OPERATOR_TOKEN) {
            v1 -= v2;
        } else {
            unget_token(&token);
        }
    }
    return v1;
}

double
parse_line(void) {
    double value;

    st_look_ahead_token_exists = 0;
    value = parse_expression();

    return value;
}

int
main(int argc, char **argv) {
    char line[LINE_BUF_SIZE];
    double value;

    while (fgets(line, LINE_BUF_SIZE, stdin) != NULL) {
        time_t time_start = time(NULL);
        set_line(line);
        value = parse_line();
        time_t time_end = time(NULL);
        printf(">>%f,time:%f.
", value, difftime(time_end, time_start));
    }

    return 0;
}

//#lexicalanalyzer.c#
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include "token.h"

static char *st_line;
static int st_line_pos;

typedef enum {
    INITIAL_STATUS,
    IN_INT_PART_STATUS,
    DOT_STATUS,
    IN_FRAC_PART_STATUS
} LexerStatus;

void
get_token(Token *token) {
    int out_pos = 0;
    LexerStatus status = INITIAL_STATUS;
    char current_char;

    token->kind = BAD_TOKEN;
    while (st_line[st_line_pos] != '') {
        current_char = st_line[st_line_pos];
        if ((status == IN_INT_PART_STATUS || status == IN_FRAC_PART_STATUS)
            && !isdigit(current_char) && current_char != '.') {
            token->kind = NUMBER_TOKEN;
            sscanf(token->str, "%lf", &token->value);
            return;
        }
        if (isspace(current_char)) {
            if (current_char == '
') {
                token->kind = END_OF_LINE_TOKEN;
                return;
            }
            st_line_pos++;
            continue;
        }

        if (out_pos >= MAX_TOKEN_SIZE - 1) {
            fprintf(stderr, "token too long.
");
            exit(1);
        }
        token->str[out_pos] = st_line[st_line_pos];
        st_line_pos++;
        out_pos++;
        token->str[out_pos] = '';

        if (current_char == '+') {
            token->kind = ADD_OPERATOR_TOKEN;
            return;
        } else if (current_char == '-') {
            token->kind = SUB_OPERATOR_TOKEN;
            return;
        } else if (current_char == '*') {
            token->kind = MUL_OPERATOR_TOKEN;
            return;
        } else if (current_char == '/') {
            token->kind = DIV_OPERATOR_TOKEN;
            return;
        } else if (current_char == '(') {
            token->kind = LEFT_PAREN_TOKEN;
            return;
        } else if (current_char == ')') {
            token->kind = RIGHT_PAREN_TOKEN;
            return;
        } else if (isdigit(current_char)) {
            if (status == INITIAL_STATUS) {
                status = IN_INT_PART_STATUS;
            } else if (status == DOT_STATUS) {
                status = IN_FRAC_PART_STATUS;
            }
        } else if (current_char == '.') {
            if (status == IN_INT_PART_STATUS) {
                status = DOT_STATUS;
            } else {
                fprintf(stderr, "syntax error.
");
                exit(1);
            }
        }
    }
}

void
set_line(char *line) {
    st_line = line;
    st_line_pos = 0;
}

#if 0
void
parse_line(void)
{
    Token token;
    st_line_pos = 0;

    for (;;) {
        get_token(&token);
        if (token.kind == END_OF_LINE_TOKEN) {
          break;
        } else {
            printf("kind..%d, str..%s
", token.kind, token.str);
        }
    }
}

int
main(int argc, char **argv)
{
    while (fgets(st_line, LINE_BUF_SIZE, stdin) != NULL) {
        parse_line();
    }

    return 0;
}
#endif