我的循环查找素数的问题

Issue with my loop finding primes

本文关键字:问题 循环 查找 我的      更新时间:2023-10-16

我需要输出来读取数字,然后判断数字是否为素数。出于某种原因,当它达到11时,它不会输出它是素数,而只是打印11 12那个数字不是素数。

我知道while循环有一个逻辑问题,但我想不通。感谢您的帮助。

int main()
{
    bool isPrime = true;
    int sqrtNum;
    int divisor = 3;
    for(int i = 0; i < 100; i++)
    {
        cout << i << "t";

        if (i == 0 || i == 1)
            cout << "That number is not prime." << endl;
        else if (i == 2)
            cout << "That number is prime." << endl;
        else if (i % 2 == 0)
            cout << "That number is not prime." << endl;
        else
        {
            sqrtNum = static_cast<int> (sqrt(static_cast<double>(i)));
            while (divisor <= sqrtNum)
            {
                if (i % divisor == 0)
                {
                    cout << "That number is not prime." << endl;
                    isPrime = false;
                    break;
                }
                else
                {
                    divisor = divisor + 2;
                }
            }
            if (isPrime)
            {
                cout << "That number is prime" << endl;
            }
        }
    }
    system("pause");
    retu

从注释中可以清楚地看到,您忘记在循环中重置isPrimedivisor的值。为了避免这样的错误,最好只在使用这些变量的范围内定义它们。

int main()
{
    for(int i = 0; i < 100; i++)
    {
        cout << i << "t";

        if (i == 0 || i == 1)
            cout << "That number is not prime." << endl;
        else if (i == 2)
            cout << "That number is prime." << endl;
        else if (i % 2 == 0)
            cout << "That number is not prime." << endl;
        else
        {
            bool isPrime = true;
            int divisor = 3;
            int sqrtNum = static_cast<int> (sqrt(static_cast<double>(i)));