Question

我试图制作一个程序，要求用户输入3个数字。每个数字必须介于1和1000之间。我遇到了while循环的问题，因为我无法弄清楚循环无法无限运行的正确陈述。如果该数字小于1但大于1000，则会要求用户再次输入一个数字。

# include <iostream>

using namespace std;

int a, b,c, sum;


int main (){


    cout << "Enter first number:";
    cin >> a;
        while ( a <=1 || a<=1000)
            cout<< "Entered number must between 1 .. 1000";

    cout << "Enter second number:";
    cin >> b;
        if ( b <=1 || b <=1000)
            cout<< "Entered number must between 1 .. 1000";

    cout << "Enter third number:";
    cin >> c;

        if ( c <=1 || c <=1000)
            cout<< "Entered number must between 1 .. 1000";

    sum = a+b+c;

    cout << a <<"+"<<b << "+"<< c << "Your sum is: " << sum << endl;


    return 0;

}

Answer 1

这是一个密集的示例，应该向您展示一些技巧：

<强> Live On Coliru

#include <iostream>
#include <limits>

namespace {
    void ignore_rest_of_line(std::istream& is) {
        is.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    }

    void try_recover(std::istream& is) {
        if (is.eof())
            throw std::runtime_error("Unexpected end of input");
        is.clear();
        ignore_rest_of_line(is);
    }
}

template <typename T, typename Validator>
T prompt(std::string label, Validator f) {
    T value;
    while (true) {
        std::cout << "Enter " << label << ": ";
        if (std::cin >> value) {
            if (f(value))
                return value;
        } else {
            std::cerr << "Invalid input\n";
            try_recover(std::cin);
        }
    }

    // unreachable
}

int main() {
    auto validate = [](int i) { return i>=2 && i<=999; };
    int a = prompt<int>("first number (2..999)", validate);
    int b = prompt<int>("second number (2..999)", validate);
    int c = prompt<int>("third number (2..999)", validate);

    int sum = a + b + c;

    std::cout << a << "+" << b << "+" << c << " Your sum is: " << sum << std::endl;
}

打印

Enter first number (2..1000): a
Invalid input
Enter first number (2..1000): 0
Enter first number (2..1000): 99999
Enter first number (2..1000): 2
Enter second number (2..1000): 2
Enter third number (2..1000): 2
2+2+2 Your sum is: 6

验证每个号码是否在特定条件

1 个答案: