我正在尝试创建一个错误消息，如果在数组中输入的数据小于零，输入验证

Question

该方法允许用户输入一年中每个月的降雨量。 我试图阻止数据小于零存储在数组中。 我正在使用do-while循环，但我似乎无法弄清楚如何检查输入是否小于零。 谢谢你的帮助，欢呼！

public static double[] getRainFall()
    {
        double[] rainfallMonths = new double[12];
        double[] rainfall = new double[12];

        do
        {
            for(int x = 0; x < rainfallMonths.length; x++)
            {
                    System.out.print("What is the rainfall for month #" + (x + 1) + ": ");
                rainfallMonths[x] = keyboard.nextDouble();
                rainfall[x] = rainfallMonths[x];

                if(rainfallMonths < 0)
                {
                    System.out.println("Input is Invalid");
                }
            }
        }while(rainfallMonths < 0);


        for(int count = 0; count < rainfallMonths.length; count++)
        {
            System.out.println("Rainfall Month #" + (count + 1) + ": " + rainfall[count]);
        }

        return rainfall;
    }

Answer 1

你的逻辑有点偏，更不用说你试图将数组与int进行比较......

一，逻辑......

do 
    for x = 0 to rainfallMonths.length -1 do
        ... get input...
while value < 0

这里的问题是，你已经在for-next循环中为数组的所有元素分配了输入，但是你试图验证在for-next之外输入的值，这可能永远不会返回一个有效的结果......现在为时已晚......

相反，你想要扭转逻辑......

for x = 0 to rainfallMonths.length -1 do
    do 
        value = get input from user
    while value < 0
    rainfallMonths[x] = value

接下来， rainfallMonths是对数组的引用，这实际上并不是你想要检查的，你需要检查一个它的值或元素，例如......

while (rainfallMonths[x] < 0);

如果这些都没有意义......

public static double[] getRainFall()
{
    double[] rainfallMonths = new double[12];
    double[] rainfall = new double[12];

    for(int x = 0; x < rainfallMonths.length; x++)
    {
        double input = 0;
        System.out.print("What is the rainfall for month #" + (x + 1) + ": ");
        do {
            rainfallMonths[x] = keyboard.nextDouble();
            rainfall[x] = rainfallMonths[x];
            if(input < 0)
            {
                System.out.println("Input is Invalid");
            }
        } while (rainfallMonths[x] < 0);    
    }


    for(int count = 0; count < rainfallMonths.length; count++)
    {
        System.out.println("Rainfall Month #" + (count + 1) + ": " + rainfall[count]);
    }

    return rainfall;
}

你可能想对数组进行复习，这应该有所帮助;）

Answer 2

double temp = -1;
for(int x = 0; x < rainfallMonths.length; x++)
        {
            System.out.print("What is the rainfall for month #" + (x + 1) + ": ");
            temp = keyboard.nextDouble();
            if(temp < 0)
            {
                System.out.println("Input is Invalid");
                x--; //if you want the user to maybe try to repeat this month again?
            }
            else
            {
                rainfallMonths[x] = keyboard.nextDouble();
                rainfall[x] = rainfallMonths[x];
            }
        }