在while循环中使用扫描仪时，如何“灌注”一个循环并创建一个标记？

Question

// 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();
}

I am confused about this. What would I insert in the while and inside the body and make a sentinel of -1? Also what is the appropriate conditional to be placed in the while loop? So how would I answer the question of "Add the conditional to the loop so it continues as long as num is not equal to the sentinel"?

Answer 1

Does this work for you?

int sentinel = -1;

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

Answer 2

Use a do..while

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

Answer 3

I would use something like this

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
}

Answer 4

To avoid checking if num has reached the sentinel value both in the while condition and again inside the loop before using num , use break with an infinite loop.

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