小C语言--词法分析程序

傷城~ 2022-05-13 12:10 166阅读 0赞

Problem Description  
小C语言文法  
1. <程序>→()\{<声明序列><语句序列>\}  
2. <声明序列>→<声明序列><声明语句>|<声明语句>|<空>  
3. <声明语句>→<标识符表>;  
4. <标识符表>→<标识符>,<标识符表>|<标识符>  
5. <语句序列>→<语句序列><语句>|<语句>  
6. <语句>→< if语句>|< while语句>|< for语句>|<复合语句>|<赋值语句>  
7. < if语句>→< if关键字>(<表达式>)<复合语句>|(<表达式>)<复合语句>< else关键字><复合语句>  
8. < while语句>→< while关键字>(<表达式>)<复合语句>  
9. < for语句>→< for关键字>(<表达式>;<表达式>;<表达式>)<复合语句>  
10. <复合语句>→\{<语句序列>\}  
11. <赋值语句>→<表达式>;  
12. <表达式>→<标识符>=<算数表达式>|<布尔表达式>  
13. <布尔表达式>→<算数表达式> |<算数表达式><关系运算符><算数表达式>  
14. <关系运算符>→>|<|>=|<=|==|!=  
15. <算数表达式>→<算数表达式>+<项>|<算数表达式>-<项>|<项>  
16. <项>→<项>\*<因子>|<项>/<因子>|<因子>  
17. <因子>→<标识符>|<无符号整数>|(<算数表达式>)  
18. <标识符>→<字母>|<标识符><字母>|<标识符><数字>  
19. <无符号整数>→<数字>|<无符号整数><数字>  
20. <字母>→a|b|…|z|A|B|…|Z  
21. <数字>→0|1|2|3|4|5|6|7|8|9

1.  < main关键字>→main
2.  < if关键字>→if
3.  < else关键字>→else
4.  < for关键字>→for
5.  < while关键字>→while
6.  < int关键字>→int

每行单词数不超过10个  
小C语言文法如上，现在我们对小C语言写的一个源程序进行词法分析，分析出关键字、自定义标识符、整数、界符  
和运算符。  
关键字：main if else for while int  
自定义标识符：除关键字外的标识符  
整数：无符号整数  
界符：\{ \} ( ) , ;  
运算符：= + - \* / < <= > >= == !=

Input  
输入一个小C语言源程序，源程序长度不超过2000个字符，保证输入合法。

Output  
按照源程序中单词出现顺序输出，输出二元组形式的单词串。

(单词种类,单词值)

单词一共5个种类：

关键字：用keyword表示  
自定义标识符：用identifier表示  
整数：用integer表示  
界符：用boundary表示  
运算符：用operator表示

每种单词值用该单词的符号串表示。

Sample Input  
main()  
\{  
int a, b;  
if(a == 10)  
\{  
a = b;  
\}  
\}  
Sample Output  
(keyword,main)  
(boundary,()  
(boundary,))  
(boundary,\{)  
(keyword,int)  
(identifier,a)  
(boundary,,)  
(identifier,b)  
(boundary,;)  
(keyword,if)  
(boundary,()  
(identifier,a)  
(operator,==)  
(integer,10)  
(boundary,))  
(boundary,\{)  
(identifier,a)  
(operator,=)  
(identifier,b)  
(boundary,;)  
(boundary,\})  
(boundary,\})  
Hint  
Source  
cai++

代码一

#include <iostream>
    #include<string>
    //只有输入正确的源代码程序才能正确
    using namespace std;
    
    int main()
    {
        string keyword[] = { "main", "int", "if", "else", "while", "for" };
        string s;
        while (cin >> s)
        {
            int len = s.length();
            int i = 0;
            while (i < len)
            {
                string tp = "";
    
                if (s[i] == '+' || s[i] == '-' ||
                    s[i] == '*' || s[i] == '/')
                {
                    printf("(operator,%c)\n", s[i]);
                    i++;
                }
    
                if (s[i] == '<' || s[i] == '>' ||
                    s[i] == '=' || s[i] == '!')
                {
                    tp = "";
                    tp = s[i];
                    i++;
                    if (s[i] == '=')
                    {
                        tp += s[i];
                        i++;
                    }
                    cout << "(" << "operator" << "," << tp << ")" << endl;
                }
                else if (s[i] == ';' || s[i] == ',' ||
                    s[i] == ')' || s[i] == '(' ||
                    s[i] == '}' || s[i] == '{')
                {
                    printf("(boundary,%c)\n", s[i]);
                    i++;
                }
                else if (s[i] >= '0' && s[i] <= '9')//数字判断
                {
                    tp = "";
                    tp = s[i];
                    i++;
                    while (s[i] >= '0' && s[i] <= '9')
                    {
                        tp += s[i];
                        i++;
                    }
                    cout << "(" << "integer" << "," << tp << ")" << endl;
                }//标识符判断
                else if (s[i] == '_'
                    || (s[i] <= 'z' && s[i] >= 'a')
                    || (s[i] <= 'Z' && s[i] >= 'A'))
                {
                    tp = "";
                    tp = s[i];
                    i++;
                    while ((s[i] >= '0' && s[i] <= '9')
                        || s[i] == '_'
                        || (s[i] <= 'z' && s[i] >= 'a')
                        || (s[i] <= 'Z' && s[i] >= 'A'))
                    {
                        tp += s[i];
                        i++;
                    }
                    int flag = 1;
                    for (int i = 0; i < 6; i++)
                    {
                        if (tp.compare(keyword[i]) == 0)
                        {
                            cout << "(" << "keyword" << "," << tp << ")" << endl;
                            flag = 0;
                            break;
                        }
                    }
                    if(flag)
                        cout << "(" << "identifier" << "," << tp << ")" << endl;
                }
            }
        }
        //system("pause");
        return 0;
    }

代码二

#include <iostream>
    #include<string>
    //只有输入正确的源代码程序才能正确
    using namespace std;
    
    int main()
    {
        string keyword[] = { "main", "int", "if", "else", "while", "for" };
        string s;
        while (cin >> s)
        {
            int len = s.length();
            int i = 0;
            while (i < len)
            {
                string tp = "";
    
                if (s[i] == '+' || s[i] == '-' ||
                    s[i] == '*' || s[i] == '/')
                {
                    printf("(operator,%c)\n", s[i]);
                    i++;
                }
    
                if (s[i] == '<' || s[i] == '>' ||
                    s[i] == '=' || s[i] == '!')
                {
                    tp = "";
                    tp = s[i];
                    i++;
                    if (s[i] == '=')
                    {
                        tp += s[i];
                        i++;
                    }
                    cout << "(" << "operator" << "," << tp << ")" << endl;
                }
                else if (s[i] == ';' || s[i] == ',' ||
                    s[i] == ')' || s[i] == '(' ||
                    s[i] == '}' || s[i] == '{')
                {
                    printf("(boundary,%c)\n", s[i]);
                    i++;
                }
                else if (s[i] >= '0' && s[i] <= '9')//数字判断
                {
                    tp = "";
                    tp = s[i];
                    i++;
                    while (s[i] >= '0' && s[i] <= '9')
                    {
                        tp += s[i];
                        i++;
                    }
                    cout << "(" << "integer" << "," << tp << ")" << endl;
                }//标识符判断
                else if (s[i] == '_'
                    || (s[i] <= 'z' && s[i] >= 'a')
                    || (s[i] <= 'Z' && s[i] >= 'A'))
                {
                    tp = "";
                    tp = s[i];
                    i++;
                    while ((s[i] >= '0' && s[i] <= '9')
                        || s[i] == '_'
                        || (s[i] <= 'z' && s[i] >= 'a')
                        || (s[i] <= 'Z' && s[i] >= 'A'))
                    {
                        tp += s[i];
                        i++;
                    }
                    int flag = 1;
                    for (int i = 0; i < 6; i++)
                    {
                        if (tp.compare(keyword[i]) == 0)
                        {
                            cout << "(" << "keyword" << "," << tp << ")" << endl;
                            flag = 0;
                            break;
                        }
                    }
                    if (flag)
                        cout << "(" << "identifier" << "," << tp << ")" << endl;
                }
                else
                {
                    i++;
                }
            }
        }
        //system("pause");
        return 0;
    }