使用C/C++语言编写PL/0编译程序的语义分析程序，并生成四元式形式的中间代码

PL/0编译程序主要包含了词法分析、语法分析和语义分析三个部分。语法分析阶段通常会生成语法树作为中间结果，而语义分析阶段则会对语法树进行遍历，进行类型检查、作用域检查和代码生成等操作。

下面是一个示例代码，演示如何使用C++语言编写PL/0编译程序的语义分析程序，并生成四元式形式的中间代码：

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

// Token类，表示词法分析的结果
class Token {
public:
    enum class Type {
        Identifier,
        Number,
        Operator,
        Keyword,
        Delimiter,
        EndOfFile
    };

    Token(Type type, string value): type_(type), value_(value) {}

    Type type() const { return type_; }
    string value() const { return value_; }

private:
    Type type_;
    string value_;
};

// 符号表项类，表示一个变量或常量的信息
class Symbol {
public:
    enum class Type {
        Variable,
        Constant
    };

    Symbol(Type type, string name, int level, int address, int value = 0)
        : type_(type), name_(name), level_(level), address_(address), value_(value) {}

    Type type() const { return type_; }
    string name() const { return name_; }
    int level() const { return level_; }
    int address() const { return address_; }
    int value() const { return value_; }

private:
    Type type_;
    string name_;
    int level_;
    int address_;
    int value_;
};

// 四元式类，表示中间代码的一条指令
class Quadruple {
public:
    enum class Operator {
        Add,
        Sub,
        Mul,
        Div,
        Assign,
        Load,
        Store,
        Push,
        Pop,
        Jmp,
        JmpIf,
        JmpIfNot,
        Call,
        Ret
    };

    Quadruple(Operator op, string arg1, string arg2, string result)
        : op_(op), arg1_(arg1), arg2_(arg2), result_(result) {}

    Operator op() const { return op_; }
    string arg1() const { return arg1_; }
    string arg2() const { return arg2_; }
    string result() const { return result_; }

private:
    Operator op_;
    string arg1_;
    string arg2_;
    string result_;
};

// PL/0编译程序类，包含词法分析、语法分析和语义分析等功能
class Compiler {
public:
    Compiler(string source): source_(source) {}

    void compile() {
        // 词法分析
        tokenize();

        // 语法分析
        parse();

        // 语义分析
        analyze();

        // 代码生成
        generate();
    }

private:
    // 词法分析部分
    void tokenize() {
        // TODO: 实现词法分析部分
    }

    // 语法分析部分
    void parse() {
        // TODO: 实现语法分析部分
    }

    // 语义分析部分
    void analyze() {
        // 初始化符号表
        symbols_.push_back(Symbol(Symbol::Type::Variable, "", 0, 0));    // 空符号表

        // 遍历语法树，进行类型检查、作用域检查和代码生成
        analyzeNode(root_);
    }

    // 对语法树节点进行语义分析
    void analyzeNode(Node* node) {
        if (node->type == Node::Type::Program) {
            // 程序节点，遍历子节点
            for (auto child : node->children) {
                analyzeNode(child);
            }
        } else if (node->type == Node::Type::Block) {
            // 块节点，进入新的作用域并遍历子节点
            enterScope();
            for (auto child : node->children) {
                analyzeNode(child);
            }
            exitScope();
        } else if (node->type == Node::Type::VarDecl) {
            // 变量声明节点，将变量添加到符号表中
            for (auto child : node->children) {
                if (child->type == Node::Type::Identifier) {
                    string name = child->token.value();
                    int address = allocate();
                    symbols_.push_back(Symbol(Symbol::Type::Variable, name, currentLevel(), address));
                }
            }
        } else if (node->type == Node::Type::ConstDecl) {
            // 常量声明节点，将常量添加到符号表中
            for (auto child : node->children) {
                if (child->type == Node::Type::Identifier) {
                    string name = child->token.value();
                    int value = stoi(child->sibling->token.value());
                    symbols_.push_back(Symbol(Symbol::Type::Constant, name, currentLevel(), 0, value));
                }
            }
        } else if (node->type == Node::Type::AssignStmt) {
            // 赋值语句节点，生成赋值指令
            string varName = node->token.value();
            Symbol* symbol = findSymbol(varName);
            if (symbol == nullptr) {
                error("Undefined variable: " + varName);
            }
            analyzeNode(node->children[0]);
            quadruples_.push_back(Quadruple(Quadruple::Operator::Assign, pop(), "", symbol->name()));
        } else if (node->type == Node::Type::ReadStmt) {
            // 读取语句节点，生成读取指令
            string varName = node->token.value();
            Symbol* symbol = findSymbol(varName);
            if (symbol == nullptr) {
                error("Undefined variable: " + varName);
            }
            quadruples_.push_back(Quadruple(Quadruple::Operator::Load, "", "", "stdin"));
            quadruples_.push_back(Quadruple(Quadruple::Operator::Store, pop(), "", symbol->name()));
        } else if (node->type == Node::Type::WriteStmt) {
            // 输出语句节点，生成输出指令
            analyzeNode(node->children[0]);
            quadruples_.push_back(Quadruple(Quadruple::Operator::Load, "", "", "stdout"));
            quadruples_.push_back(Quadruple(Quadruple::Operator::Push, pop(), "", ""));
            quadruples_.push_back(Quadruple(Quadruple::Operator::Call, "", "", "print"));
        } else if (node->type == Node::Type::IfStmt) {
            // 条件语句节点，生成条件跳转指令
            analyzeNode(node->children[0]);
            quadruples_.push_back(Quadruple(Quadruple::Operator::JmpIfNot, pop(), "", ""));
            analyzeNode(node->children[1]);
        } else if (node->type == Node::Type::IfElseStmt) {
            // 条件语句（含有else分支）节点，生成条件跳转指令和无条件跳转指令
            analyzeNode(node->children[0]);
            quadruples_.push_back(Quadruple(Quadruple::Operator::JmpIfNot, pop(), "", ""));
            analyzeNode(node->children[1]);
            int label1 = allocateLabel();
            quadruples_.push_back(Quadruple(Quadruple::Operator::Jmp, "", "", toLabel(label1)));
            setLabel(label1);
            analyzeNode(node->children[2]);
        } else if (node->type == Node::Type::WhileStmt) {
            // 循环语句节点，生成条件跳转指令和无条件跳转指令
            int label1 = allocateLabel();
            setLabel(label1);
            analyzeNode(node->children[0]);
            quadruples_.push_back(Quadruple(Quadruple::Operator::JmpIfNot, pop(), "", ""));
            analyzeNode(node->children[1]);
            quadruples_.push_back(Quadruple(Quadruple::Operator::Jmp, "", "", toLabel(label1)));
        } else if (node->type == Node::Type::CallStmt) {
            // 调用语句节点，生成调用指令
            string funcName = node->token.value();
            quadruples_.push_back(Quadruple(Quadruple::Operator::Call, "", "", funcName));
        } else if (node->type == Node::Type::ReturnStmt) {
            // 返回语句节点，生成返回指令
            analyzeNode(node->children[0]);
            quadruples_.push_back(Quadruple(Quadruple::Operator::Ret, "", "", ""));
        } else if (node->type == Node::Type::Expression) {
            // 表达式节点，生成表达式指令
            analyzeExpression(node);
        } else if (node->type == Node::Type::Identifier) {
            // 标识符节点，生成加载指令
            string varName = node->token.value();
            Symbol* symbol = findSymbol(varName);
            if (symbol == nullptr) {
                error("Undefined variable: " + varName);
            }
            quadruples_.push_back(Quadruple(Quadruple::Operator::Load, "", "", symbol->name()));
            push(symbol->name());
        } else if (node->type == Node::Type::Number) {
            // 数字节点，生成常量指令
            int value = stoi(node->token.value());
            string name = toConstant(value);
            quadruples_.push_back(Quadruple(Quadruple::Operator::Load, "", "", name));
            push(name);
        } else if (node->type == Node::Type::Operator) {
            // 运算符节点，生成运算指令
            analyzeExpression(node);
        }
    }

    // 对表达式节点进行语义分析
    void analyzeExpression(Node* node) {
        if (node->type == Node::Type::Expression) {
            analyzeExpression(node->children[0]);
            if (node->children.size() == 3) {
                analyzeExpression(node->children[2]);
                string arg2 = pop();
                string arg1 = pop();
                string result = newTemp();
                switch (node->children[1]->token.type()) {
                case Token::Type::Operator:
                    switch (node->children[1]->token.value()[0]) {
                    case '+':
                        quadruples_.push_back(Quadruple(Quadruple::Operator::Add, arg1, arg2, result));
                        break;
                    case '-':
                        quadruples_.push_back(Quadruple(Quadruple::Operator::Sub, arg1, arg2, result));
                        break;
                    case '*':
                        quadruples_.push_back(Quadruple(Quadruple::Operator::Mul, arg1, arg2, result));
                        break;
                    case '/':
                        quadruples_.push_back(Quadruple(Quadruple::Operator::Div, arg1, arg2, result));
                        break;
                    }
                    break;
                case Token::Type::Keyword:
                    if (node->children[1]->token.value() == "and") {
                        quadruples_.push_back(Quadruple(Quadruple::Operator::Mul, arg1, arg2, result));
                    } else if (node->children[1]->token.value() == "or") {
                        quadruples_.push_back(Quadruple(Quadruple::Operator::Add, arg1, arg2, result));
                        quadruples_.push_back(Quadruple(Quadruple::Operator::Push, result, "", ""));
                        quadruples_.push_back(Quadruple(Quadruple::Operator::Load, "", "", toConstant(0)));
                        quadruples_.push_back(Quadruple(Quadruple::Operator::JmpIfNot, pop(), "", ""));
                        quadruples_.push_back(Quadruple(Quadruple::Operator::Push, toConstant(1), "", ""));