关于#c++#的问题，请各位专家解答！

一直报''没有与这些操作数匹配的 "<<" 运算符 "

```c++
#include
#include
#pragma once
using namespace std;
class Account {
    double balance;
public:
    Account() {
        balance = 0.0;
    }
    Account(double balance_) {
        balance = balance_;
    }
    void deposit(double amount) {
        balance += amount;
    };
    void withdraw(double amount) {
        auto temp{ 0.0 };
        if (balance < amount) {
            temp = balance;
            balance = 0;
            return; temp;
        }
        else {
            balance -= amount;
            return; amount;
        }
    }

    int main() {
        Account a1;
        Account a2 = Account(100.0);
        a1.deposit(9.0);
        cout << a1.withdraw(9.0) <withdraw(10.0) << endl;
        cout << Account(1000.0).withdraw(1001.0) << endl;
    };
};

```

望采纳！点击该回答右侧的“采纳”按钮即可采纳！！！兄弟你的代码错误不少呢！！！我给你等会给你列出来，有时间会帮你改代码，希望给博主个采纳呀!!!
一共四个问题！
1.auto temp{ 0.0 } 中的花括号应改为小括号。
2.在 withdraw 函数中，当 balance 小于 amount 时，return; temp; 应改为 return temp;，否则应改为 return amount;。
3.int main() 函数中的 cout << Account(1000.0).withdraw(1001.0) << endl; 中的 Account(1000.0) 应改为 Account a3(1000.0)，否则会出现“未解引用的指针”的错误。
4.在类定义的最后应加上 };，否则会出现“未定义的标识符”的错误。
修改后的代码如下：

#include<iostream>
#include<string>
#pragma once
using namespace std;

class Account {
  double balance;
  public:
    Account() {
      balance = 0.0;
    }
    Account(double balance_) {
      balance = balance_;
    }
    void deposit(double amount) {
      balance += amount;
    }
    double withdraw(double amount) {
      if (balance < amount) {
        balance = 0;
        return balance;
      }
      else {
        balance -= amount;
        return amount;
      }
    }
};

int main() {
  Account a1;
  Account a2 = Account(100.0);
  a1.deposit(9.0);
  cout << a1.withdraw(9.0) <<endl;
  cout << a2.withdraw(10.0) << endl;
  cout << Account(1000.0).withdraw(1001.0) << endl;
  return 0;
}

有几个问题

• ① main 函数不应该在 Account 类内部。它应该在外部，如下所示：

#include<iostream>
#include<string>
#pragma once
using namespace std;

class Account {
    double balance;
public:
    Account() {
        balance = 0.0;
    }
    Account(double balance_) {
        balance = balance_;
    }
    void deposit(double amount) {
        balance += amount;
    };
    void withdraw(double amount) {
        auto temp{ 0.0 };
        if (balance < amount) {
            temp = balance;
            balance = 0;
            return temp;
        }
        else {
            balance -= amount;
            return amount;
        }
    }
};

int main() {
    Account a1;
    Account a2 = Account(100.0);
    a1.deposit(9.0);
    cout << a1.withdraw(9.0) <<endl;
    cout << a2.withdraw(10.0) << endl;
    cout << Account(1000.0).withdraw(1001.0) << endl;
}

• ② withdraw 函数应该返回一个 double 值，但它目前返回的是 void。这就是 "没有与这些操作数匹配的 "<<" 运算符" 的错误信息的原因。你可以通过将函数的返回类型更改为 double 来解决这个问题，如下所示：

double withdraw(double amount) {
    auto temp{ 0.0 };
    if (balance < amount) {
        temp = balance;
        balance = 0;
        return temp;
    }
    else {
        balance -= amount;
        return amount;
    }
}

因为你的类Account 函数void withdraw没有返回，改成这样就ok,还有类结束那个大括号弄到main前面去

double withdraw(double amount)
    {
        auto temp{0.0};
        if (balance < amount)
        {
            temp = balance;
            balance = 0;
            return temp;
        }
        else
        {
            balance -= amount;
            return amount;
        }
    }

谢谢各位,现在问题已经解决