C++ 輸入驗證整數。 num 的輸入不應是字符/字符串、十進制值或負數

Question

出於某種原因，這只能驗證字符/字符串。 如何使其驗證負值和十進制值？

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

您的代碼存在一些問題：

1. 不用寫cin >> num 2次，在while循環的條件下只獲取一次輸入就夠了
2. 不是!(cin >> num || num < 0) ，而是!(cin >> num) || num < 0 !(cin >> num) || num < 0 as !(cin >> num)將報告字符串的輸入，而num < 0將報告負值的輸入
3. 由於輸入了一個十進制值， cin會將該值存儲到. 並留下剩余的數字. 在沒有消耗它們的緩沖區中，您可以添加條件cin.peek() == '.' 檢查用戶是否輸入了十進制值

這是您的編輯代碼：

#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;
}

這是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.