Java “我该怎么做？”；素数；在while循环中使用scanner时创建一个循环和哨兵？

我对此感到困惑。我应该在while和身体内部插入什么，使-1成为哨兵？另外，while循环中要放置的适当条件是什么？那么，我该如何回答“将条件添加到循环中，这样只要num不等于sentinel，循环就会继续”的问题呢

// Create a constant sentinel of -1
// “Prime” the loop
// Add the conditional to the loop so it continues
// as long as num is not equal to the sentinel

Scanner keyboard = new Scanner(System.in);   //data will be entered thru keyboard
while (...) {
    //process data
    num = keyboard.nextInt();
}

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使用

do..while

int sentinel = -1;

while(num != sentinel)
{
   // process data
   num = keyboard.nextInt();
}

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我会用这样的东西

int num = -1;
do {
    // process data 
    num = keyboard.nextInt(); 
} while(num != -1);

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为避免检查

num

是否在

while

条件下以及在使用

num

之前再次在循环内达到sentinel值，请使用无限循环的

break

int num = 0;
while(num != - 1)
{
num = keyboard.nextInt();
// whatever you want to do with num might want to put code in an if like
if(num != -1)
{
//do code
}
//also you could get the number at then end so you can do processing without the if     statement above
}

Scanner keyboard = new Scanner(System.in);   //data will be entered thru keyboard
for (;;) {
    num = keyboard.nextInt();
    if (num == -1) {
        break;
    }
    // use num
}