C++ C++；仅限正整数

这是我第一次使用Stackoverflow。 我正在做一个程序来找出一辆车的MPG。我想知道如何使cin语句只接受正整数？而且，如果您输入了无效的输入，您可以重置它吗？我不确定这是否有意义。我上课不必这么做。我只是好奇怎么做。这是代码

#include <iostream>
using namespace std;

int main()
{
double tank, miles, mpg;

cout << "Hello. This is a program that calculates the MPG ( Miles Per Gallon) for      your\n" ;
cout << "vehicle\n" << endl;
cout << "Please enter how many gallons your vehicle can hold\n" << endl;
cin >> tank;
cout << endl;
cout << "Please enter how many miles that have been driven on a full tank\n" <<endl;
cin >> miles;
cout << endl;

mpg = (miles)/(tank);
cout << "Your vehicle recieves " << mpg << " miles per gallon\n" << endl;
system ("pause");
return 0;
}

#包括
使用名称空间std；
int main（）
{
双油箱，英里，每加仑；
coutiostreams不是用于构建复杂用户界面的工具包。除非您想编写自己的相当复杂的流来包装通常的流，否则您无法让它（a）只接受正整数或（b）礼貌地与键入其他内容的用户交互

您应该只读取cin中的行，并在查看得到的内容后打印您自己的错误提示等。
而不是

cin >> miles;

试一试

while（（cin>>英里）<0）
cout
cout不过，在命令行环境中有两种标准方法可以实现这一点

您可以将cin语句困在一个循环中，直到输入有效的输入后才会释放。这是验证CLI输入的“标准”方法，而不仅仅是有符号的数字

do
{
    cout << "\nPlease enter...";
    cin >> tank;
}
while (tank < 0)

do
{
水槽；
}
而（油箱<0）

while语句中的条件是验证数据的地方。您还可以使用if语句解释输入无效的原因

另一种方法是简单地强制值为正，只需执行
tank=fabs（tank）；
，它取
tank
变量的绝对值（即正）。
这是我的无限循环代码
    So this is my code for an infinite loop
    1: So main will call the "Get_number()" function
    2: Get number will accept an int from the user
    3(A): If int is greater than 0, go into loop
    3(B): Else, display to user "Invalid Input" and then call the function
          "Get_number()" again creating an infinite loop until the user
           enters a value greater than 0



    #include <iostream>  // Access the input output stream library
    #include <fstream>   // Access to the fstream library (used to read and write to files)
    #include <chrono> // Needed to access "std::chrono_literals"
    #include <thread> // Needed to access "namespace std::this_thread"

    using std::fstream; // this will allow us to use the fstream (we'll be able to read and write to files)
    using std::ios;     // needed for iostream (used to be able to tell fstream to read and/or write to a file and that it's reading/writing a binary file)
    using std::cout;    // need this statment to access cout (to display info to user)
    using std::cin;     // need this statment to access cin (to gather info from user)
    using std::endl;    // need this statment to access endl (will end the line)
    using namespace std::this_thread; // This will allow me to use "Sleep_For" or "Sleep_Until"
    using namespace std::chrono_literals; // This will allow the use of measurements of time such as ns, us, s, h, etc.

    //Prototypes***************************************************************************************************
    void shellSort(int read[], int readLength); //Making Prototype (Declaring our function) so that compiler knows not to worry about it
    void Get_number();
    void Write_to_file(int user_input_of_how_many_random_numbers_to_generate); //Making Prototype (Declaring our function) so that compiler knows not to worry about it
    void Read_from_file(int user_input_of_how_many_random_numbers_to_generate);//Making Prototype (Declaring our function) so that compiler knows not to worry about it
    //*************************************************************************************************************

    void main()
    {
        Get_number();

        system("pause>>void"); // will let the console pause untill user presses any button to continue

    }

    /**************************************************************************************************************
    * Purpose: This function will gather a positive integer from the user and use it to generate that many
    *          random numbers!
    *
    * Precondition: None
    *
    *
    * Postcondition:
    *           Would've gathered the number of random numbers the user wanted to generate and then gone into the 
    *           Write_to_file and Read_from_file function
    *
    **************************************************************************************************************/

    void Get_number()
    {
        int user_input_of_how_many_random_numbers_to_generate = 0; //make variable that will accept the int value the user wants to generate random numbers
        cout << "Please Enter A Number Greater Than Zero:" << endl; // displays to user to enter a number greater than zero
        cin >> user_input_of_how_many_random_numbers_to_generate; // will accept the value the user inputted and place it in the "user_input_of_how_many_random_numbers_to_generate" variable
        system("cls"); // Will clear the screen
        if (user_input_of_how_many_random_numbers_to_generate > 0) // if user input is greater than zero, enter this
        {

            Write_to_file(user_input_of_how_many_random_numbers_to_generate); // will bring up the "Write_to_file" function
            Read_from_file(user_input_of_how_many_random_numbers_to_generate); // will bring up the "Read_from_file" function
        }
        else // else enter this
        {
            cout << "invalid input!" << endl; // display to user "invalid input"
            sleep_for(2s); // system will pause for 2 seconds allowing the user to read the message of "invalid input"
            system("cls"); // console will be cleared
            Get_number(); // Get_number function will be entered creating an infinate loop untill the user's input is valid!
        }
    }

1:So main将调用“Get_number（）”函数
2:Get number将接受来自用户的int
3（A）：如果int大于0，则进入循环
3（B）：否则，向用户显示“无效输入”，然后调用该函数
“Get_number（）”再次创建无限循环，直到用户
输入一个大于0的值
#包括//访问输入输出流库
#包括//访问fstream库（用于读取和写入文件）
#包括//访问“std:：chrono_文字”所需的
#包括//访问“命名空间std:：this_线程”所需的
使用std:：fstream；//这将允许我们使用fstream（我们将能够读取和写入文件）
使用std:：ios；//iostream需要（用于告诉fstream读取和/或写入文件，并且它正在读取/写入二进制文件）
使用std:：cout；//需要此语句访问cout（向用户显示信息）
使用std:：cin；//需要此语句访问cin（从用户收集信息）
使用std:：endl；//需要此语句访问endl（将结束该行）
使用命名空间std:：this_thread；//这将允许我使用“Sleep_For”或“Sleep_Until”
使用名称空间std:：chrono_literals；//这将允许使用时间度量，如ns、us、s、h等。
//原型***************************************************************************************************
void shellSort（int read[]，int readLength）；//制作原型（声明我们的函数），这样编译器就不用担心了
void Get_number（）；
void Write_to_file（int user_input_of_how_numbers_random_numbers_to_generate）；//制作原型（声明我们的函数），这样编译器就不必担心了
void Read_from_file（int user_input_of_how_numbers_random_numbers_to_generate）；//制作原型（声明我们的函数），这样编译器就不用担心了
//*************************************************************************************************************
void main（）
{
获取_编号（）；
系统（“暂停>>无效”）；//将让控制台暂停，直到用户按下任何按钮继续
}
/**************************************************************************************************************
*用途：此函数将从用户处收集一个正整数，并使用它生成多个正整数
*随机数！
*
*前提条件：无
*
*
*后置条件：
*会收集用户想要生成的随机数，然后进入
*将\u写入\u文件并从\u文件函数中读取\u
*
**************************************************************************************************************/
void Get_number（）
{
int user_input of_how_mandom_numbers_to_generate=0；//生成一个变量，该变量将接受用户想要生成随机数的int值
cout user\u input\u of\u how\u numbers\u random\u \u to \u generate；//将接受用户输入的值，并将其放入“user\u input\u of \u how\u numbers\u random\u to \u generate”变量中
系统（“cls”）；//将清除屏幕
if（user\u input\u of\u how\u numbers\u random\u numbers\u to\u generate>0）//如果用户输入大于零，请输入
{
写入文件（用户输入要生成的随机数）；//将显示“写入文件”功能
从文件读取（用户输入要生成的随机数）；//将显示“从文件读取”功能
}
else//else输入这个
{
不能回答你的问题，但如果你想要整数，你不应该要求双倍。先要一个整数，然后处理它不是正的事实。更好的方法是读取字符串，然后解析它们，以确保这是必需的/如果有人输入了不需要的内容，则标记错误，并给他们另一个opp机会。是的，你不能从键盘上实际移除键。人们会犯输入错误。表达式
cin>>miles
返回
cin
，因此我不确定这应该如何工作。这也不会对用户进行任何错误检查
do
{
    cout << "\nPlease enter...";
    cin >> tank;
}
while (tank < 0)

    So this is my code for an infinite loop
    1: So main will call the "Get_number()" function
    2: Get number will accept an int from the user
    3(A): If int is greater than 0, go into loop
    3(B): Else, display to user "Invalid Input" and then call the function
          "Get_number()" again creating an infinite loop until the user
           enters a value greater than 0



    #include <iostream>  // Access the input output stream library
    #include <fstream>   // Access to the fstream library (used to read and write to files)
    #include <chrono> // Needed to access "std::chrono_literals"
    #include <thread> // Needed to access "namespace std::this_thread"

    using std::fstream; // this will allow us to use the fstream (we'll be able to read and write to files)
    using std::ios;     // needed for iostream (used to be able to tell fstream to read and/or write to a file and that it's reading/writing a binary file)
    using std::cout;    // need this statment to access cout (to display info to user)
    using std::cin;     // need this statment to access cin (to gather info from user)
    using std::endl;    // need this statment to access endl (will end the line)
    using namespace std::this_thread; // This will allow me to use "Sleep_For" or "Sleep_Until"
    using namespace std::chrono_literals; // This will allow the use of measurements of time such as ns, us, s, h, etc.

    //Prototypes***************************************************************************************************
    void shellSort(int read[], int readLength); //Making Prototype (Declaring our function) so that compiler knows not to worry about it
    void Get_number();
    void Write_to_file(int user_input_of_how_many_random_numbers_to_generate); //Making Prototype (Declaring our function) so that compiler knows not to worry about it
    void Read_from_file(int user_input_of_how_many_random_numbers_to_generate);//Making Prototype (Declaring our function) so that compiler knows not to worry about it
    //*************************************************************************************************************

    void main()
    {
        Get_number();

        system("pause>>void"); // will let the console pause untill user presses any button to continue

    }

    /**************************************************************************************************************
    * Purpose: This function will gather a positive integer from the user and use it to generate that many
    *          random numbers!
    *
    * Precondition: None
    *
    *
    * Postcondition:
    *           Would've gathered the number of random numbers the user wanted to generate and then gone into the 
    *           Write_to_file and Read_from_file function
    *
    **************************************************************************************************************/

    void Get_number()
    {
        int user_input_of_how_many_random_numbers_to_generate = 0; //make variable that will accept the int value the user wants to generate random numbers
        cout << "Please Enter A Number Greater Than Zero:" << endl; // displays to user to enter a number greater than zero
        cin >> user_input_of_how_many_random_numbers_to_generate; // will accept the value the user inputted and place it in the "user_input_of_how_many_random_numbers_to_generate" variable
        system("cls"); // Will clear the screen
        if (user_input_of_how_many_random_numbers_to_generate > 0) // if user input is greater than zero, enter this
        {

            Write_to_file(user_input_of_how_many_random_numbers_to_generate); // will bring up the "Write_to_file" function
            Read_from_file(user_input_of_how_many_random_numbers_to_generate); // will bring up the "Read_from_file" function
        }
        else // else enter this
        {
            cout << "invalid input!" << endl; // display to user "invalid input"
            sleep_for(2s); // system will pause for 2 seconds allowing the user to read the message of "invalid input"
            system("cls"); // console will be cleared
            Get_number(); // Get_number function will be entered creating an infinate loop untill the user's input is valid!
        }
    }