关于#c++#的问题，请各位专家解答！

Question

一直报''没有与这些操作数匹配的 "<<" 运算符 "

```c++
#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;
    };
};

```

Answer 1

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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;
}