Question

我正在尝试验证双数据类型的输入，我已成功部分因为如果用户输入的第一件事是字母，它将输出错误消息，但是如果用户在开头输入一个数字然后程序接受它，虽然它不应该。有想法该怎么解决这个吗？到目前为止，这是我的代码：

void circleArea(double pi)                                                          
{
    double radius = 0.0;
    bool badInput;

    do
    {
        cout << "*================*\n";
        cout << " Area of a circle\n";
        cout << "*================*\n\n";
        cout << "Please enter the radius of your circle (numerics only):\n\n";
        cin >> radius;

        badInput = cin.fail();
        cin.clear();
        cin.ignore(numeric_limits<streamsize>::max(), '\n');
    } while (badInput == true);

    system("CLS");
    cout << "The area of your Circle is:\n\n" << radius*radius*pi << "cm^2" << endl << endl;    
    exitSystem();
}

Answer 1

典型的习惯用法是读取cout << "*================*\n"; cout << " Area of a circle\n"; cout << "*================*\n\n"; cout << "Please enter the radius of your circle (numerics only):\n\n"; if (!(cin >> radius)) { cerr << "Invalid input, try again.\n"; } else { // radius is valid }语句中的值：

private void button_Click(object sender, RoutedEventArgs e)
    {
        TextBox tBox = new TextBox();
        tBox.Width = 500;
        tBox.Header = "Notes";
        tBox.PlaceholderText = "Type your notes here";
     }

这不处理数字后跟字母或无效符号的情况，例如“1.23A”或“1＃76”。对于这些情况，您必须以字符串形式阅读文本并执行更详细的解析。

Answer 2

另一种可能性，使用正则表达式检查输入的字符串是否为字符串！

// Example program
#include <iostream>
#include <string>
#include <boost/regex.hpp>
#include <boost/lexical_cast.hpp>

const boost::regex is_number_regex("^\\d+(()|(\\.\\d+)?)$");
//If I didn't make a mistake this regex matches positive decimal numbers and integers
int main()
{
    double radius;
    std::string inputstring;
    std::cin >> inputstring;
    boost::smatch m;
    if( boost::regex_search(inputstring, m, is_number_regex))
    {
        radius = boost::lexical_cast<double>( inputstring );
        std::cout <<"Found value for radius:  "<< radius << std::endl;
    }
    else
    {
        std::cerr << "Error" << std::endl;
    }
}

如果您需要负数，科学数字......，请调整正则表达式。

验证无法正常运行双C ++

2 个答案: