C ++（负验证不起作用 [英] C++ (negative verification is not working

问题描述

测试cin的非数字，非零和非负值并进入循环。无法看到为什么对值<= 0的测试不起作用。它应该输出：

Testing cin for non numeric, non zero,and non negative values and entering loop. Cannot see why the test for values <=0 portion is not working. it should output:

cout << "Invalid value input\n";

在此先感谢您发现可能是一个愚蠢的错误。

Thanks in advance for catching what is probably a silly error.

#include <iostream>
using namespace std;

int main()
{
    unsigned int integer;

    cout<< "Enter a non negative number greater than 0: ";
    cin>> integer;

    do
    {
         while(!cin || integer <= 0)//validation condition
         {
             cout << "Invalid value input\n";
             cin.clear();
             cin.ignore(200, '\n');
             cout<< "Enter a non negative number greater than 0: ";
             cin>> integer;
         }
         cout<< "Enter a non negative number greater than 0: ";
         cin>> integer;
    } while(integer !=1);

    return 0;
}

推荐答案

由于 unsigned int integer; 。

将此值更改为int integer可检查否定验证。


无符号int值的范围是0到4,294,967,295（4字节）

因此，无符号-1表示4,294,967,295，因为-1位表示形式是111〜11（ 32个）


您可以检查 2的补语二进制减法，以及-1如何变成2 ^ 32-1

It's not working because of unsigned int integer; .
Changing this to int integer to check for negative verification.

Range of the value of an unsigned int is 0 to 4,294,967,295 (4 bytes)
So -1 in unsigned means 4,294,967,295 as -1 bit representation is 111~11 (32 Ones)

You may check 2's Complement for binary bit subtraction and how -1 became 2^32-1

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