java 使用哨兵控制的循环
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Using sentinel-controlled loop
提问by user1864508
I'm having trouble with an exercise asking to have a user prompt a name and echoes that name to the screen until user enters a sentinel value. I understand this is a sentinel-controlled loop but I'm stuck on the fact that I'm dealing with entering a name instead of an integer. I tried to follow a program in my book which only explains how to use a sentinel value with integers but not with String "name". I tried looking up this answer and saw something like name.equals("stop") if it even applies to this. and looked it up on the APIs and still didn't find it helpful. I would like to see how it applies as a whole.
Note: here is what I have done so far and I want to know how far off I am.
我在练习要求用户提示名称并将该名称回显到屏幕上时遇到问题，直到用户输入标记值。我知道这是一个哨兵控制的循环，但我坚持要输入名称而不是整数的事实。我试图遵循我书中的一个程序，该程序仅解释了如何将标记值与整数一起使用，而不是与字符串“名称”一起使用。我尝试查找这个答案并看到类似 name.equals("stop") 的内容，如果它甚至适用于此。并在 API 上查找它，但仍然没有发现它有帮助。我想看看它作为一个整体是如何应用的。
注意：这是我到目前为止所做的，我想知道我离我有多远。
import java.util.*;
public class SentinelControlledLoop {
static Scanner console = new Scanner(System.in);
static final int SENTINEL = #;
public static void main (String[] args) {
String name;
System.out.println("Enter a name " + "ending with " + SENTINEL);
String name = reader.next();
while (!name.equals(“stop”)) {
name = reader.next();
}
回答by joval
do {
name = reader.next();
} while (name.lastIndexOf(SENTINEL) == -1);
I assume that name cannot contain the sentinel in it. In other case, change == -1to
我认为该名称中不能包含哨兵。在其他情况下，更改== -1为
!= length(name) - 1
PS. You're declaring String nametwice.
附注。你声明了String name两次。
PS2. Even better condition:
PS2。更好的条件：
while (!name.endsWith(String.valueOf(SENTINEL));
回答by 5377037
The use of sentinel for loop:
哨兵for循环的使用：
In a sentinel controlled loop the change part depends on data from the user. It is awkward to do this inside a for statement. So the change part is omitted from the for statement and put in a convenient location.
在哨兵控制的循环中，更改部分取决于来自用户的数据。在 for 语句中执行此操作很尴尬。所以更改部分从 for 语句中省略并放在一个方便的位置。
import java.util.Scanner;
class EvalSqrt
{
public static void main (String[] args )
{
Scanner scan = new Scanner( System.in );
double x;
System.out.print("Enter a value for x or -1 to exit: ") ;
x = scan.nextDouble();
for ( ; x >= 0.0 ; )
{
System.out.println( "Square root of " + x + " is " + Math.sqrt( x ) );
System.out.print("Enter a value for x or -1 to exit: ") ;
x = scan.nextDouble();
}
}
}
For more details: https://chortle.ccsu.edu/java5/Notes/chap41/ch41_13.html
更多详情：https: //chortle.ccsu.edu/java5/Notes/chap41/ch41_13.html
