C++如何循环这个东西(初学者)

Question

我正在弄清楚如何循环我的代码，现在它让我感到困惑，任何帮助将不胜感激，我是这里的初学者所以请不要骂我。

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

int main()
{
    string str;
    char ans;

    cout << "CONVERSION\n\n";
    cout << "Base 11 to Decimal\n";
        a:cout << "Base 11: ";
        getline(std::cin, str);
        const auto bad_loc = str.find_first_not_of("0123456789aA");
        if (bad_loc != std::string::npos)
        {
            std::cerr << "Invalid Input\n";
            goto a;
        }
        unsigned long ul = std::stoul(str, nullptr, 11);
        cout << "Decimal: " << ul << "\n\n";
        cout << "Do you want to continue (Y/N)? ";
        cin >> ans;
        if (ans == 'y')
        {
            goto a;
        }
        else if (ans == 'n')
        {
            cout <<"Name:\tXXXXXXXX\n";
            cout <<"Course:\tXXXXXXXX";
            cout <<"Section:\tXXXXXXXX\n";
            cout <<"Schedule:\tXXXXXXXX\n";
            cout <<"Professor:\tXXXXXXXX\n";
        }
        return 0;
}

输出应该是这样的

CONVERSION

Base 11 to Decimal
Base 11: B
Invalid Input!

Base 11: A
//blank
Do you want to continue (Y/N)? X
Invalid Answer! (Y/N)? Y
//blank
Base11:

我的问题是(1) 程序在“base11:”循环后停止，每当我回答 Y 和 (2) 如果我回答来自“你想要...”的任何字母，程序将结束。 (3) 如何解决这个问题。

Answer 1

我们初学者应该互相帮助不是吗？:)

程序看起来像下面这样

#include <iostream>
#include <string>
#include <limits>

int main()
{
    std::cout << "CONVERSION\n\n";
    std::cout << "Base 11 to Decimal\n";

    char ans;

    do
    {        
        std::string s;

        bool valid_input = false;
        while ( !valid_input )
        {
            std::cout << "Base 11: ";

            if ( !std::getline( std::cin, s ) ) break;

            if ( !( valid_input = s.find_first_not_of( "0123456789aA" ) == std::string::npos ) )
            {                
                std::cout << "Invalid Input\n\n";
            }
        }

        if ( !valid_input )
        {
            std::cout << "See you later!" << std::endl;
            break;
        }

        unsigned long value = std::stoul( s, nullptr, 11 );

        std::cout << "Decimal: " << value << "\n\n";

        std::cout << "Do you want to continue (Y/N)? ";
        std::cin >> ans;
        std::cin.ignore( std::numeric_limits<std::streamsize>::max(), '\n' );
    } while ( ans == 'y' || ans == 'Y' );

    std::cout <<"Name:\tXXXXXXXX\n";
    std::cout <<"Course:\tXXXXXXXX";
    std::cout <<"Section:\tXXXXXXXX\n";
    std::cout <<"Schedule:\tXXXXXXXX\n";
    std::cout <<"Professor:\tXXXXXXXX\n";

    return 0;
}

如果输入看起来像

B
A
Y
C
AA
N

那么输出就是

CONVERSION

Base 11 to Decimal
Base 11: B
Invalid Input

Base 11: A
Decimal: 10

Do you want to continue (Y/N)? Y
Base 11: C
Invalid Input

Base 11: AA
Decimal: 120

Do you want to continue (Y/N)? N
Name:   XXXXXXXX
Course: XXXXXXXXSection:    XXXXXXXX
Schedule:   XXXXXXXX
Professor:  XXXXXXXX

注意语句

std::cin.ignore( std::numeric_limits<std::streamsize>::max(), '\n' );

跳过使用operator >>输入ans后输入的换行符。