Question

我已经编写了程序并运行了它，但我不知道如何防止println语句在我用无效数字运行时出现。它基本上是一个你输入月份和时间的程序。一天（数值），输出将是季节。这是代码：

Thread.sleep()

Answer 1

写：

file.open( games );
if( file.is_open() )
{
    for( int x = 0; x < BOARD_SIZE; x++) 
    { 
        for (int y = 0; y < BOARD_SIZE; y++) 
        { 
            char point = 'C'; 
            if( !file.get( point ) ) 
                std::cout << "Error reading " << x << "," << y << std::endl; 
            chessBoards[x][y] = point;
        } 
    }
}

然后在最后一个if之前检查：

String season = null;

Answer 2

一种方法可能是：

boolean invalid = false;

if (month <= 3)
{
    season = winter;
}
else if (month <= 6)
{
    season = spring;
}
else if (month <= 9)
{
    season = summer;
}
else if (month <= 12)
{
    season = fall;
} else {
    invalid = true;
}

if(invalid){
    System.out.println("The value is invalid.");
} else {
    System.out.println(season);
}

您唯一要做的就是记住日期是否无效。因此，您需要一个布尔标志invalid。

Answer 3

最简单的方法是测试如下。否则，您将设置一个真正的假标志并在最后测试它以确定要打印的内容。请注意，系统默认设置为无效，因此错误打印输出将是季节无效

另一种方法是使用适当的情况进行switch语句，并将默认设置为make season无效。这样就不需要做所有的elseif语句了。但是，我正在展示if elseif，以保持原来的问题。

System.out.println("Enter a month: ");
month = in.nextInt();

System.out.println("Enter a day: ");
day = in.nextInt();

String winter = "winter";
String spring = "spring";
String summer = "summer";
String fall = "fall";
String invalid = "invalid";
String season = invalid; // Set the default to invalid

System.out.println("Month="+ month +" Day= "+day);

if (month > 12 || month < 1)
{
    season = invalid;
}
elseif (month > 9)
{
    season = fall;
} 
if (month > 6)
{
    season = summer;
}
else if (month > 3)
{
    season = spring;
}
else
{
    season = winter;
}
System.out.println("season is ", season);

Answer 4

将season设置为null，并在打印前检查null。删除最后一个else

if (season != null) {
    System.out.println(season);
} else {
    System.out.println("The value is invalid.");
}

Answer 5

我建议封装if语句。您无需使用null。并且您只能获得有效季节的输出。

if (month > 12 || month < 1)
{
    season = invalid;
} else {
    if (month > 9)
    {
        season = fall;
    } 
    else if (month > 6)
    {
        season = summer;
    }
    else if (month > 3)
    {
        season = spring;
    }
    else
    {
        season = winter;
    }
    System.out.println("season is ", season);
}

我有一个if语句问题

5 个答案: