我们可以在 C++ 中限制用户输入吗？

Question

问题是当用户输入 = 9999999999 时，控制台将返回所有值。如果有人试图为 a, b = 9999999999 设置值，我想通过使用简单的else if语句来限制此输入，那么用户必须收到我在代码中定义的警告。我可以通过使用 double 而不是 int 来控制它，但这不是解决方案。

#include <iostream>
using namespace std;
main()
{
    int a, b, c, d;
    cout << "Enter Value for A: ";
    cin >> a;

    cout << "Enter Value for B: ";
    cin >> b;

    if (a > b)
        {
        cout << "A is Greater than B " << endl; //This will be printed only if the statement is True
        }
    else if ( a < b )
        {
        cout << "A is Less than B " << endl; //This will be printed if the statement is False
        }
        else if ( a, b > 999999999 )
        {
        cout << " The Value is filtered by autobot !not allowed " << endl; //This will be printed if the statement is going against the rules
        }
     else
        {
        cout << "Values are not given or Unknown " << endl; //This will be printed if the both statements are unknown
        }

    cout << "Enter Value for C: ";
    cin >> c;

    cout << "Enter Value for D: ";
    cin >> d;

    if (c < d)
    {
        cout << c << " < " << d << endl; //This will be printed if the statement is True
        }
        else if ( c > d )
        {
        cout << "C is Greater than D " << endl; //This will be printed if the statement is False
        }
        else
        {
        cout << c << " unknown " << d << endl; //This will be printed if the statement is Unknown
        }
}

Answer 1

这是一个确保有效输入的示例函数。我也让它接受了最小值和最大值，但你不一定需要它们，因为 999999999int无论如何都会超出范围，这会导致cin失败。不过它会等待有效的输入。

int getNum( int min, int max ) {
    int val;
    while ( !( cin >> val ) || val < min || val > max ) {
        if ( !cin ) {
            cin.clear();
            cin.ignore( 1000, '\n' );
        }
        cout << "You entered an invalid number\n";
    }
    return val;
}

int main() {
    int a = getNum( 0, 12321 );
}

编辑：嗯，现在你刚刚修改了你的问题，使用简单的 else if 语句，改变答案。那么答案是否定的。由于cin会失败，您实际上无法进行检查。此外，它永远不会是真的，因为999999999它比INT_MAX我能想到的任何实现都要大。