C++ 输入验证整数。 num 的输入不应是字符/字符串、十进制值或负数

Question

出于某种原因，这只能验证字符/字符串。 如何使其验证负值和十进制值？

cout << "Please enter a whole number: ";
while (!(cin >> num || num < 0)){ 
    cin.clear();
    cin.ignore(10000, '\n');
    cout << "Invalid! A whole number is positive and an integer.     \n";
    cout << "Please enter a whole number again: ";
    cin >> num;

Answer 1

您的代码存在一些问题：

1. 不用写cin >> num 2次，在while循环的条件下只获取一次输入就够了
2. 不是!(cin >> num || num < 0) ，而是!(cin >> num) || num < 0 !(cin >> num) || num < 0 as !(cin >> num)将报告字符串的输入，而num < 0将报告负值的输入
3. 由于输入了一个十进制值， cin会将该值存储到. 并留下剩余的数字. 在没有消耗它们的缓冲区中，您可以添加条件cin.peek() == '.' 检查用户是否输入了十进制值

这是您的编辑代码：

#include <iostream>

using namespace std;

int main() {
    int num = 0;
    cout << "Please enter a whole number: ";
    while (!(cin >> num) || num < 0 || cin.peek() == '.') {
        cin.clear();
        cin.ignore(10000, '\n');
        cout << "Invalid! A whole number is positive and an integer.     \n";
        cout << "Please enter a whole number again: ";
    
    }

    return 0;
}

这是output的一些例子：

Please enter a whole number: asdasd
Invalid! A whole number is positive and an integer.
Please enter a whole number again: -12312
Invalid! A whole number is positive and an integer.
Please enter a whole number again: 1.23
Invalid! A whole number is positive and an integer.
Please enter a whole number again: -123.2
Invalid! A whole number is positive and an integer.
Please enter a whole number again: 123

C:\Users\abdo\source\repos\Project55\Debug\Project55.exe (process 31896) exited with code 0.