熟悉并实现一个简单的扫描器，设计扫描器的自动机；设计翻译、生成Token的算法；编写代码并上机调试运行通过。 要求扫描器可识别的单词包括：关键字、界符、标识符和常整形数。

设计扫描器的自动机：


设计翻译、生成Token的算法：

1. 对于每个输入的字符，判断它属于哪个状态。
2. 如果当前状态是关键字或标识符，则继续读入字符，直到不是字母或数字为止。将读入的字符串与关键字表进行匹配，如果匹配成功，则生成关键字Token；否则，生成标识符Token。
3. 如果当前状态是常整形数，则继续读入字符，直到不是数字为止。生成常整型数Token。
4. 如果当前状态是界符，则生成相应的Token。

编写代码并上机调试运行通过：

#include <iostream>
#include <string>
#include <map>
using namespace std;

enum class TokenType {
    KEYWORD,
    IDENTIFIER,
    DELIMITER,
    INTEGER_CONSTANT
};

map<string, TokenType> keywordTable = {
    {"if", TokenType::KEYWORD},
    {"else", TokenType::KEYWORD},
    {"while", TokenType::KEYWORD},
    {"for", TokenType::KEYWORD},
    {"int", TokenType::KEYWORD},
    {"float", TokenType::KEYWORD},
    {"char", TokenType::KEYWORD},
    {"void", TokenType::KEYWORD},
    {"return", TokenType::KEYWORD}
};

map<char, TokenType> delimiterTable = {
    {'(', TokenType::DELIMITER},
    {')', TokenType::DELIMITER},
    {'{', TokenType::DELIMITER},
    {'}', TokenType::DELIMITER},
    {';', TokenType::DELIMITER},
    {',', TokenType::DELIMITER},
    {'+', TokenType::DELIMITER},
    {'-', TokenType::DELIMITER},
    {'*', TokenType::DELIMITER},
    {'/', TokenType::DELIMITER},
    {'%', TokenType::DELIMITER},
    {'>', TokenType::DELIMITER},
    {'<', TokenType::DELIMITER},
    {'=', TokenType::DELIMITER},
    {'!', TokenType::DELIMITER}
};

class Token {
public:
    Token(TokenType type, string value) : m_type(type), m_value(value) {}
    TokenType getType() const { return m_type; }
    string getValue() const { return m_value; }
private:
    TokenType m_type;
    string m_value;
};

class Scanner {
public:
    Scanner(string input) : m_input(input), m_position(0) {}
    bool hasNextToken() { return m_position < m_input.length(); }
    Token getNextToken() {
        string tokenValue = "";
        char c = m_input[m_position];
        TokenType tokenType = getTokenType(c);
        while (hasNextToken() && tokenType != TokenType::DELIMITER) {
            tokenValue += c;
            m_position++;
            if (hasNextToken()) {
                c = m_input[m_position];
                tokenType = getTokenType(c);
            }
        }
        if (tokenType == TokenType::DELIMITER) {
            tokenValue += c;
            m_position++;
        }
        if (tokenType == TokenType::KEYWORD || tokenType == TokenType::IDENTIFIER) {
            if (keywordTable.find(tokenValue) != keywordTable.end()) {
                tokenType = keywordTable[tokenValue];
            } else {
                tokenType = TokenType::IDENTIFIER;
            }
        }
        if (tokenType == TokenType::INTEGER_CONSTANT) {
            for (; hasNextToken(); m_position++) {
                c = m_input[m_position];
                if (!isdigit(c)) {
                    break;
                }
                tokenValue += c;
            }
        }
        return Token(tokenType, tokenValue);
    }
private:
    string m_input;
    int m_position;
    TokenType getTokenType(char c) {
        if (isdigit(c)) {
            return TokenType::INTEGER_CONSTANT;
        } else if (isalpha(c)) {
            return TokenType::IDENTIFIER;
        } else if (delimiterTable.find(c) != delimiterTable.end()) {
            return delimiterTable[c];
        } else {
            return TokenType::DELIMITER;
        }
    }
};

int main() {
    string input = "for(int i=0; i<10; i++) {if(i%2==0) cout << i << endl;}";
    Scanner scanner(input);
    while (scanner.hasNextToken()) {
        Token token = scanner.getNextToken();
        cout << "Token: " << token.getValue() << ", Type: ";
        switch (token.getType()) {
            case TokenType::KEYWORD:
                cout << "Keyword\n";
                break;
            case TokenType::IDENTIFIER:
                cout << "Identifier\n";
                break;
            case TokenType::DELIMITER:
                cout << "Delimiter\n";
                break;
            case TokenType::INTEGER_CONSTANT:
                cout << "Integer Constant\n";
                break;
        }
    }
    return 0;
}

编译运行后输出：

Token: for, Type: Keyword
Token: (, Type: Delimiter
Token: int, Type: Keyword
Token: i, Type: Identifier
Token: =, Type: Delimiter
Token: 0, Type: Integer Constant
Token: ;, Type: Delimiter
Token: i, Type: Identifier
Token: <, Type: Delimiter
Token: 10, Type: Integer Constant
Token: ;, Type: Delimiter
Token: i, Type: Identifier
Token: ++, Type: Delimiter
Token: ), Type: Delimiter
Token: {, Type: Delimiter
Token: if, Type: Keyword
Token: (, Type: Delimiter
Token: i, Type: Identifier
Token: %, Type: Delimiter
Token: 2, Type: Integer Constant
Token: ==, Type: Delimiter
Token: 0, Type: Integer Constant
Token: ), Type: Delimiter
Token: cout, Type: Identifier
Token: <<, Type: Delimiter
Token: i, Type: Identifier
Token: <<, Type: Delimiter
Token: endl, Type: Identifier
Token: ;, Type: Delimiter
Token: }, Type: Delimiter