C++ 什么是cin.peek，它有什么作用？ #包括 使用名称空间std； int main（） { //声明数据类型 int NumChild；//var const int BaseFee=150；//常数 //用户欢迎+说明 cout

。该代码正在检查以确保流中的下一个字符是文件的结尾或行的结尾，而不会从流中提取字符并破坏后续的有效输入

它不能接受浮点数，因为

cin>>NumChild

将读取

int

，并在到达小数点后立即停止。例如：输入“3.14”。

NumChild

将包含3.“.14”保留在流中，因此peek将读取

。

，而不是文件的结尾或换行符，并打印错误消息

然后它继续执行程序的其余部分，因为没有任何命令它停止。在提供有效输入之前，需要围绕输入进行循环以继续请求更多输入

一个简单的例子：

#include <iostream>
using namespace std;
int main() 
{
//Declare data types
int NumChild; //var
const int BaseFee = 150; //constant

//Welcome + Instructions for users
cout << "Welcome to IOU Secondary School" << endl <<endl<< "How many 
children are attending the school this year? "<<endl;

//Nested IF-ELSE (error checking)
if (cin >> NumChild)/

    {

        //do not accept any non-integer values
        if (cin.peek() == EOF|| cin.peek() == '\n' )
        {

        }
        else
        { 

            cout <<endl<< "Error: enter a whole number."<<endl<< "The total 
   amount below represents the initial number entered e.g. if 5.7 is entered, the fee will be calculated according to 5 children" << endl;//error message for float entry
            cin.ignore(100, '\n'); //read and discard up to 100 characters from the input buffer, or until a newline is read
            cin.clear();//resets any error flags in the cin stream

        }
    }
    else
    {
        // Edit: You should probably also clear the steam
        cin.ignore(100, '\n');//read and discard up to 100 characters from 
        the input buffer, or until a newline is read
        cin.clear(); //resets any error flags in the cin stream
        cout << "Error: Restart the program and enter a number";

    }

    //nested IF statement (Calculation of fees)
if(NumChild == 1) //1 child attending
{
cout<<endl<<"The total cost of your child's fees are $"<< BaseFee+50 << 
endl;
}

if(NumChild == 2) //2 children attending
  {
cout<<endl<<"The total cost of your children's fees are $"<< (BaseFee*2)+85 
<< endl;
  }

if(NumChild == 3)//3 children attending
  {
cout<<endl<<"The total cost of your children's fees are $"<< (BaseFee*3)+110 
<< endl;
  }

if(NumChild > 3) //More than children attending
  {
cout<<endl<<"The total cost of your children's fees are $"<< 
(BaseFee*NumChild)+150 << endl;
  }
}

。该代码正在进行检查，以确保流中的下一个字符是文件的结尾或行的结尾，而不会从流中提取字符并损坏后续的有效输入

它不能接受浮点数，因为

cin>>NumChild

将读取

int

，并在到达小数点后立即停止。例如：输入“3.14”。

NumChild

将包含3.“.14”保留在流中，因此peek将读取

。

，而不是文件的结尾或换行符，并打印错误消息

然后它继续执行程序的其余部分，因为没有任何命令它停止。在提供有效输入之前，需要围绕输入进行循环以继续请求更多输入

一个简单的例子：

#include <iostream>
using namespace std;
int main() 
{
//Declare data types
int NumChild; //var
const int BaseFee = 150; //constant

//Welcome + Instructions for users
cout << "Welcome to IOU Secondary School" << endl <<endl<< "How many 
children are attending the school this year? "<<endl;

//Nested IF-ELSE (error checking)
if (cin >> NumChild)/

    {

        //do not accept any non-integer values
        if (cin.peek() == EOF|| cin.peek() == '\n' )
        {

        }
        else
        { 

            cout <<endl<< "Error: enter a whole number."<<endl<< "The total 
   amount below represents the initial number entered e.g. if 5.7 is entered, the fee will be calculated according to 5 children" << endl;//error message for float entry
            cin.ignore(100, '\n'); //read and discard up to 100 characters from the input buffer, or until a newline is read
            cin.clear();//resets any error flags in the cin stream

        }
    }
    else
    {
        // Edit: You should probably also clear the steam
        cin.ignore(100, '\n');//read and discard up to 100 characters from 
        the input buffer, or until a newline is read
        cin.clear(); //resets any error flags in the cin stream
        cout << "Error: Restart the program and enter a number";

    }

    //nested IF statement (Calculation of fees)
if(NumChild == 1) //1 child attending
{
cout<<endl<<"The total cost of your child's fees are $"<< BaseFee+50 << 
endl;
}

if(NumChild == 2) //2 children attending
  {
cout<<endl<<"The total cost of your children's fees are $"<< (BaseFee*2)+85 
<< endl;
  }

if(NumChild == 3)//3 children attending
  {
cout<<endl<<"The total cost of your children's fees are $"<< (BaseFee*3)+110 
<< endl;
  }

if(NumChild > 3) //More than children attending
  {
cout<<endl<<"The total cost of your children's fees are $"<< 
(BaseFee*NumChild)+150 << endl;
  }
}

---

输入流上的“peek”函数（在您的例子中是

cin

）从流中检索下一个字符，而不实际使用它。这意味着您可以“预览”输入中的下一个字符，并在下次调用任何使用操作时（重载

运算符>

或

cin.read

）将读取该字符并使用它

条件

eof（）

关于您的另一个问题：如果输入无效（例如浮点值），您不会退出该函数。因此，您将继续执行并打印该值。只需使用输入流上的“peek”函数退出该函数即可（在您的情况下，
cin
）从流中检索下一个字符，而不实际使用它。这意味着您可以“预览”输入中的下一个字符，并且在下一次调用任何使用操作时（重载
操作符>
或
cin.read
）将读取该字符并使用它

条件
eof（）

关于您的另一个问题：如果输入无效（例如浮点值），您不会退出函数。因此，您将继续执行并打印值。只需使用
return 1；
退出函数即可