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基础语法 ​

概述 ​

C++是在C语言基础上发展而来的编程语言，增加了面向对象、泛型编程等特性。本节介绍C++的基础语法。

第一个C++程序 ​

cpp
#include <iostream>

int main() {
    std::cout << "Hello, World!" << std::endl;
    return 0;
}

使用命名空间 ​

cpp
#include <iostream>

using namespace std;

int main() {
    cout << "Hello, World!" << endl;
    return 0;
}

输入输出 ​

cout和cin ​

cpp
#include <iostream>
#include <string>

using namespace std;

int main() {
    string name;
    int age;

    cout << "请输入你的名字: ";
    cin >> name;

    cout << "请输入你的年龄: ";
    cin >> age;

    cout << "你好, " << name << "! 你今年 " << age << " 岁。" << endl;

    return 0;
}

读取一行 ​

cpp
#include <iostream>
#include <string>

using namespace std;

int main() {
    string line;

    cout << "请输入一行文字: ";
    cin.ignore();
    getline(cin, line);

    cout << "你输入的是: " << line << endl;

    return 0;
}

数据类型 ​

基本数据类型 ​

cpp
#include <iostream>
#include <climits>

using namespace std;

int main() {
    bool b = true;
    char c = 'A';
    int i = 42;
    short s = 100;
    long l = 1000000L;
    long long ll = 9223372036854775807LL;

    float f = 3.14f;
    double d = 3.14159265358979;
    long double ld = 3.14159265358979L;

    cout << "bool: " << b << endl;
    cout << "char: " << c << endl;
    cout << "int: " << i << endl;
    cout << "float: " << f << endl;
    cout << "double: " << d << endl;

    return 0;
}

auto关键字 ​

cpp
#include <iostream>
#include <vector>

using namespace std;

int main() {
    auto a = 10;
    auto b = 3.14;
    auto c = "hello";
    auto d = vector<int>{1, 2, 3};

    cout << "a的类型: int, 值: " << a << endl;
    cout << "b的类型: double, 值: " << b << endl;
    cout << "c的类型: const char*, 值: " << c << endl;

    return 0;
}

变量与常量 ​

const关键字 ​

cpp
#include <iostream>

using namespace std;

int main() {
    const int MAX_SIZE = 100;
    const double PI = 3.14159;

    cout << "MAX_SIZE = " << MAX_SIZE << endl;
    cout << "PI = " << PI << endl;

    return 0;
}

constexpr ​

cpp
#include <iostream>

using namespace std;

constexpr int square(int x) {
    return x * x;
}

int main() {
    constexpr int val = square(5);
    cout << "5的平方 = " << val << endl;

    return 0;
}

引用 ​

基本引用 ​

cpp
#include <iostream>

using namespace std;

int main() {
    int a = 10;
    int &ref = a;

    cout << "a = " << a << endl;
    cout << "ref = " << ref << endl;

    ref = 20;

    cout << "修改后 a = " << a << endl;
    cout << "修改后 ref = " << ref << endl;

    return 0;
}

引用作为函数参数 ​

cpp
#include <iostream>

using namespace std;

void swap(int &a, int &b) {
    int temp = a;
    a = b;
    b = temp;
}

void increment(int &n) {
    n++;
}

int main() {
    int x = 10, y = 20;

    cout << "交换前: x = " << x << ", y = " << y << endl;
    swap(x, y);
    cout << "交换后: x = " << x << ", y = " << y << endl;

    int num = 5;
    cout << "递增前: " << num << endl;
    increment(num);
    cout << "递增后: " << num << endl;

    return 0;
}

常量引用 ​

cpp
#include <iostream>
#include <string>

using namespace std;

void printString(const string &str) {
    cout << str << endl;
}

int main() {
    string s = "Hello, C++";
    printString(s);
    printString("World");

    return 0;
}

默认参数 ​

cpp
#include <iostream>

using namespace std;

int add(int a, int b = 0) {
    return a + b;
}

void printInfo(string name, int age = 18, string city = "北京") {
    cout << "姓名: " << name << endl;
    cout << "年龄: " << age << endl;
    cout << "城市: " << city << endl;
    cout << "-------------" << endl;
}

int main() {
    cout << "add(5) = " << add(5) << endl;
    cout << "add(5, 3) = " << add(5, 3) << endl;

    printInfo("张三");
    printInfo("李四", 25);
    printInfo("王五", 30, "上海");

    return 0;
}

函数重载 ​

cpp
#include <iostream>
#include <string>

using namespace std;

int add(int a, int b) {
    return a + b;
}

double add(double a, double b) {
    return a + b;
}

string add(const string &a, const string &b) {
    return a + b;
}

int add(int a, int b, int c) {
    return a + b + c;
}

int main() {
    cout << "int add: " << add(1, 2) << endl;
    cout << "double add: " << add(1.5, 2.5) << endl;
    cout << "string add: " << add("Hello, ", "World!") << endl;
    cout << "三个参数 add: " << add(1, 2, 3) << endl;

    return 0;
}

内联函数 ​

cpp
#include <iostream>

using namespace std;

inline int square(int x) {
    return x * x;
}

inline double cube(double x) {
    return x * x * x;
}

int main() {
    cout << "5的平方: " << square(5) << endl;
    cout << "3的立方: " << cube(3.0) << endl;

    return 0;
}

命名空间 ​

定义命名空间 ​

cpp
#include <iostream>

namespace Math {
    const double PI = 3.14159;

    double circleArea(double radius) {
        return PI * radius * radius;
    }

    double circleCircumference(double radius) {
        return 2 * PI * radius;
    }
}

namespace Physics {
    const double G = 9.8;

    double freeFall(double time) {
        return 0.5 * G * time * time;
    }
}

using namespace std;

int main() {
    cout << "圆面积 (r=5): " << Math::circleArea(5.0) << endl;
    cout << "圆周长 (r=5): " << Math::circleCircumference(5.0) << endl;
    cout << "自由落体距离 (t=2s): " << Physics::freeFall(2.0) << endl;

    return 0;
}

嵌套命名空间 ​

cpp
#include <iostream>

namespace Company {
    namespace Department {
        namespace HR {
            void hire() {
                std::cout << "招聘员工" << std::endl;
            }
        }

        namespace IT {
            void develop() {
                std::cout << "开发软件" << std::endl;
            }
        }
    }
}

int main() {
    Company::Department::HR::hire();
    Company::Department::IT::develop();

    return 0;
}

new和delete ​

动态内存分配 ​

cpp
#include <iostream>

using namespace std;

int main() {
    int *ptr = new int;
    *ptr = 100;
    cout << "动态分配的整数: " << *ptr << endl;
    delete ptr;

    int *arr = new int[5];
    for (int i = 0; i < 5; i++) {
        arr[i] = i * 10;
    }

    cout << "动态数组: ";
    for (int i = 0; i < 5; i++) {
        cout << arr[i] << " ";
    }
    cout << endl;

    delete[] arr;

    return 0;
}

二维数组 ​

cpp
#include <iostream>

using namespace std;

int main() {
    int rows = 3, cols = 4;

    int **matrix = new int*[rows];
    for (int i = 0; i < rows; i++) {
        matrix[i] = new int[cols];
    }

    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            matrix[i][j] = i * cols + j;
        }
    }

    cout << "二维数组:" << endl;
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            cout << matrix[i][j] << "\t";
        }
        cout << endl;
    }

    for (int i = 0; i < rows; i++) {
        delete[] matrix[i];
    }
    delete[] matrix;

    return 0;
}

string类 ​

基本操作 ​

cpp
#include <iostream>
#include <string>

using namespace std;

int main() {
    string s1 = "Hello";
    string s2 = "World";

    string s3 = s1 + " " + s2;
    cout << "拼接: " << s3 << endl;

    cout << "长度: " << s3.length() << endl;
    cout << "是否为空: " << (s3.empty() ? "是" : "否") << endl;

    s3.append("!");
    cout << "追加后: " << s3 << endl;

    s3.insert(5, ",");
    cout << "插入后: " << s3 << endl;

    s3.erase(5, 1);
    cout << "删除后: " << s3 << endl;

    cout << "子串: " << s3.substr(0, 5) << endl;

    size_t pos = s3.find("World");
    if (pos != string::npos) {
        cout << "找到World在位置: " << pos << endl;
    }

    return 0;
}

字符串比较 ​

cpp
#include <iostream>
#include <string>

using namespace std;

int main() {
    string s1 = "apple";
    string s2 = "banana";
    string s3 = "apple";

    cout << "s1 == s3: " << (s1 == s3 ? "true" : "false") << endl;
    cout << "s1 < s2: " << (s1 < s2 ? "true" : "false") << endl;
    cout << "s1.compare(s2): " << s1.compare(s2) << endl;

    return 0;
}

异常处理 ​

try-catch ​

cpp
#include <iostream>
#include <stdexcept>

using namespace std;

double divide(double a, double b) {
    if (b == 0) {
        throw runtime_error("除数不能为零");
    }
    return a / b;
}

int main() {
    try {
        cout << "10 / 2 = " << divide(10, 2) << endl;
        cout << "10 / 0 = " << divide(10, 0) << endl;
    } catch (const runtime_error &e) {
        cout << "捕获异常: " << e.what() << endl;
    }

    return 0;
}

自定义异常 ​

cpp
#include <iostream>
#include <string>
#include <stdexcept>

using namespace std;

class InsufficientFundsException : public runtime_error {
public:
    InsufficientFundsException(double balance, double amount)
        : runtime_error("余额不足"), balance(balance), amount(amount) {}

    double getBalance() const { return balance; }
    double getAmount() const { return amount; }

private:
    double balance;
    double amount;
};

class BankAccount {
public:
    BankAccount(double initialBalance) : balance(initialBalance) {}

    void withdraw(double amount) {
        if (amount > balance) {
            throw InsufficientFundsException(balance, amount);
        }
        balance -= amount;
        cout << "取款成功，余额: " << balance << endl;
    }

    double getBalance() const { return balance; }

private:
    double balance;
};

int main() {
    BankAccount account(1000);

    try {
        account.withdraw(500);
        account.withdraw(800);
    } catch (const InsufficientFundsException &e) {
        cout << e.what() << endl;
        cout << "当前余额: " << e.getBalance() << endl;
        cout << "尝试取款: " << e.getAmount() << endl;
    }

    return 0;
}

类型转换 ​

C++风格类型转换 ​

cpp
#include <iostream>

using namespace std;

int main() {
    double d = 3.14159;

    int i1 = static_cast<int>(d);
    cout << "static_cast: " << i1 << endl;

    const int ci = 10;
    int &ref = const_cast<int&>(ci);
    cout << "const_cast: " << ref << endl;

    int *ptr = reinterpret_cast<int*>(0x1000);
    cout << "reinterpret_cast: " << ptr << endl;

    return 0;
}

实践示例 ​

计算器程序 ​

cpp
#include <iostream>
#include <string>
#include <stdexcept>

using namespace std;

class Calculator {
public:
    double calculate(double a, double b, char op) {
        switch (op) {
            case '+': return add(a, b);
            case '-': return subtract(a, b);
            case '*': return multiply(a, b);
            case '/': return divide(a, b);
            default: throw invalid_argument("无效的运算符");
        }
    }

private:
    double add(double a, double b) { return a + b; }
    double subtract(double a, double b) { return a - b; }
    double multiply(double a, double b) { return a * b; }
    double divide(double a, double b) {
        if (b == 0) throw runtime_error("除数不能为零");
        return a / b;
    }
};

int main() {
    Calculator calc;

    while (true) {
        double a, b;
        char op;

        cout << "\n请输入表达式 (如 5 + 3, 输入 q 退出): ";
        cin >> a;

        if (cin.fail()) {
            string input;
            cin.clear();
            cin >> input;
            if (input == "q") break;
            cout << "输入无效，请重试" << endl;
            continue;
        }

        cin >> op >> b;

        try {
            double result = calc.calculate(a, b, op);
            cout << a << " " << op << " " << b << " = " << result << endl;
        } catch (const exception &e) {
            cout << "错误: " << e.what() << endl;
        }
    }

    cout << "再见!" << endl;
    return 0;
}

学生成绩管理 ​

cpp
#include <iostream>
#include <string>
#include <vector>
#include <iomanip>

using namespace std;

struct Student {
    string name;
    int id;
    vector<double> scores;

    double getAverage() const {
        if (scores.empty()) return 0;
        double sum = 0;
        for (double s : scores) sum += s;
        return sum / scores.size();
    }

    double getTotal() const {
        double sum = 0;
        for (double s : scores) sum += s;
        return sum;
    }
};

class GradeManager {
public:
    void addStudent(const string &name, int id) {
        students.push_back({name, id, {}});
        cout << "添加学生成功: " << name << endl;
    }

    void addScore(int id, double score) {
        for (auto &s : students) {
            if (s.id == id) {
                s.scores.push_back(score);
                cout << "添加成绩成功" << endl;
                return;
            }
        }
        cout << "未找到学生" << endl;
    }

    void displayAll() const {
        cout << "\n" << string(60, '=') << endl;
        cout << left << setw(10) << "学号"
             << setw(15) << "姓名"
             << setw(15) << "总分"
             << setw(15) << "平均分" << endl;
        cout << string(60, '-') << endl;

        for (const auto &s : students) {
            cout << left << setw(10) << s.id
                 << setw(15) << s.name
                 << setw(15) << fixed << setprecision(2) << s.getTotal()
                 << setw(15) << s.getAverage() << endl;
        }
        cout << string(60, '=') << endl;
    }

    void findStudent(int id) const {
        for (const auto &s : students) {
            if (s.id == id) {
                cout << "\n学生信息:" << endl;
                cout << "学号: " << s.id << endl;
                cout << "姓名: " << s.name << endl;
                cout << "成绩: ";
                for (double score : s.scores) {
                    cout << score << " ";
                }
                cout << "\n总分: " << s.getTotal() << endl;
                cout << "平均分: " << s.getAverage() << endl;
                return;
            }
        }
        cout << "未找到学号为 " << id << " 的学生" << endl;
    }

private:
    vector<Student> students;
};

int main() {
    GradeManager manager;

    manager.addStudent("张三", 1001);
    manager.addStudent("李四", 1002);
    manager.addStudent("王五", 1003);

    manager.addScore(1001, 85);
    manager.addScore(1001, 90);
    manager.addScore(1001, 78);

    manager.addScore(1002, 92);
    manager.addScore(1002, 88);

    manager.addScore(1003, 76);
    manager.addScore(1003, 82);
    manager.addScore(1003, 90);

    manager.displayAll();

    manager.findStudent(1001);

    return 0;
}

小结 ​

C++基础语法要点：

特性说明
引用变量的别名，必须初始化
const定义常量，不可修改
auto自动类型推导
函数重载同名函数，不同参数
默认参数函数参数默认值
命名空间避免命名冲突
new/delete动态内存管理
string字符串类

导航 ​