#include <iostream> #include <string> using namespace std; enum TokenType { BEGIN, IF, THEN, WHILE, DO, END, ID, NUM, ASSIGN, PLUS, MINUS, MUL, DIV, LPAREN, RPAREN, SEMICOLON, LESS, GREATER, NEQ, LESS_EQUAL, GREATER_EQUAL, END_OF_FILE, COLON }; struct Token { TokenType type; string lexeme; }; Token currentToken; void getNextToken() { // 词法分析的代码，略去不写，将结果保存在currentToken中 } void match(TokenType expectedType) { if (currentToken.type == expectedType) { getNextToken(); } else { cout << "error" << endl; exit(1); } } void program(); void stmts(); void stmt(); void exp(); void items(); void item(); void factors(); void factor(); void program() { match(BEGIN); stmts(); match(END); } void stmts() { stmt(); while (currentToken.type == SEMICOLON) { match(SEMICOLON); stmt(); } } void stmt() { if (currentToken.type == ID) { match(ID); match(ASSIGN); exp(); } else { cout << "error" << endl; exit(1); } } void exp() { item(); items(); } void items() { if (currentToken.type == PLUS || currentToken.type == MINUS) { match(currentToken.type); item(); items(); } } void item() { factor(); factors(); } void factors() { if (currentToken.type == MUL || currentToken.type == DIV) { match(currentToken.type); factor(); factors(); } } void factor() { if (currentToken.type == ID || currentToken.type == NUM) { match(currentToken.type); } else if (currentToken.type == LPAREN) { match(LPAREN); exp(); match(RPAREN); } else { cout << "error" << endl; exit(1); } } int main() { // 词法分析部分的代码，略去不写，将结果保存在currentToken中 program(); if (currentToken.type == TokenType::END_OF_FILE) { cout << "success" << endl; } else { cout << "error" << endl; } return 0; }

这段代码中存在一个问题，就是头文件和using namespace std;之间没有加换行符，导致编译器无法识别头文件。

正确的代码应该是：

#include <iostream> 
#include <string> 

using namespace std; 

enum TokenType { 
    BEGIN, IF, THEN, WHILE, DO, END, ID, NUM, ASSIGN, PLUS, MINUS, MUL, DIV, LPAREN, RPAREN, SEMICOLON, LESS, GREATER, NEQ, LESS_EQUAL, GREATER_EQUAL, END_OF_FILE, COLON 
}; 

struct Token { 
    TokenType type; 
    string lexeme; 
}; 

Token currentToken; 

void getNextToken() { 
    // 词法分析的代码，略去不写，将结果保存在currentToken中 
} 

void match(TokenType expectedType) { 
    if (currentToken.type == expectedType) { 
        getNextToken(); 
    } 
    else { 
        cout << "error" << endl; 
        exit(1); 
    } 
} 

void program(); 
void stmts(); 
void stmt(); 
void exp(); 
void items(); 
void item(); 
void factors(); 
void factor(); 

void program() { 
    match(BEGIN); 
    stmts(); 
    match(END); 
} 

void stmts() { 
    stmt(); 
    while (currentToken.type == SEMICOLON) { 
        match(SEMICOLON); 
        stmt(); 
    } 
} 

void stmt() { 
    if (currentToken.type == ID) { 
        match(ID); 
        match(ASSIGN); 
        exp(); 
    } 
    else { 
        cout << "error" << endl; 
        exit(1); 
    } 
} 

void exp() { 
    item(); 
    items(); 
} 

void items() { 
    if (currentToken.type == PLUS || currentToken.type == MINUS) { 
        match(currentToken.type); 
        item(); 
        items(); 
    } 
} 

void item() { 
    factor(); 
    factors(); 
} 

void factors() { 
    if (currentToken.type == MUL || currentToken.type == DIV) { 
        match(currentToken.type); 
        factor(); 
        factors(); 
    } 
} 

void factor() { 
    if (currentToken.type == ID || currentToken.type == NUM) { 
        match(currentToken.type); 
    } 
    else if (currentToken.type == LPAREN) { 
        match(LPAREN); 
        exp(); 
        match(RPAREN); 
    } 
    else { 
        cout << "error" << endl; 
        exit(1); 
    } 
} 

int main() { 
    // 词法分析部分的代码，略去不写，将结果保存在currentToken中 
    program(); 
    if (currentToken.type == TokenType::END_OF_FILE) { 
        cout << "success" << endl; 
    } 
    else { 
        cout << "error" << endl; 
    } 
    return 0; 
}