同时和比较 [英] do-while and while comparison

问题描述

do-while：

do
{ 
    i++; 
    ++j;
    System.out.println( i * j );

}
while ((i < 10) && (j*j != 25));

我正在学习do-while vs目前，并想重写上面的java片段（已经声明并初始化）使用了一段时间。以下重写代码的正确方法如下：

I am learning about do-while vs while at the moment and would like to rewrite the above java fragment (already declared and initialized) using a while instead. Are the below rewritten codes correct way to do so:

while：

while ((i < 10) && (j*j != 25))
{
    i++;  
    ++j;
    System.out.println( i * j );
}

干杯

推荐答案

do-while 与之间的区别 当进行比较时。使用 do-while ，您将在最后进行比较，因此至少进行一次迭代。

The difference between a do-while and a while is when the comparison is done. With a do-while, you'll compare at the end and hence do at least one iteration.

do
{ 
    i++; 
    ++j;
    System.out.println( i * j );

}
while ((i < 10) && (j*j != 25));

相当于：

i++; 
++j;
System.out.println( i * j );
while ((i < 10) && (j*j != 25)) {
    i++; 
    ++j;
    System.out.println( i * j );
}

一般理解

do-while 循环是退出控制循环，这意味着它在结束时退出。 而循环是一个条目控制循环，这意味着条件在开始时被测试，因此循环内的代码可能不会甚至被执行。

General comprehension

A do-while loop is an exit controlled loop which means that it exits at the end. A while loop is an entry controlled loop which means that the condition is tested at the beginning and as a consequence, the code inside the loop might not even be executed.

do {
    <block>
} while (<condition>);

相当于：

<block>
while (<condition>) {
    <block>
};

用例

一个典型的用例对于 do-while 如下：你问用户什么，你想要在输入不正确时重复操作。

Use case

A typical use case for a do-while is the following: you ask the user something and you want do repeat the operation while the input is not correct.

do {
   // Ask something
} while (input is not correct);

在这种情况下，你想要至少询问一次，它通常比使用<$更优雅c $ c> while 这需要重复代码，或添加额外条件或设置任意值以强制第一次进入循环。

In that case, you want to ask at least once and it's usually more elegant than using a while which would require either to duplicate code, or to add an extra condition or setting an arbitrary value to force entering the loop the first time.

相反，而循环更多公共，可以轻松替换 do-while （并非所有语言都有循环）。

At the opposite, while loops are much more commons and can easily replace a do-while (not all languages have both loops).

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