do-while 和 while 比较 [英] do-while and while comparison

问题描述

同时进行:

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

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

我目前正在学习 do-while 与 while，并想改用 while 重写上述 java 片段(已声明和初始化).以下重写的代码是否正确:

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:

同时:

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

干杯

推荐答案

do-while 和 while 的区别在于 when比较完成.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 循环是一个退出控制循环，这意味着它在最后退出.while 循环是一个入口控制循环，这意味着在开始时测试条件，因此，循环内的代码甚至可能不会被执行.>

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

do-while 的一个典型用例如下:你问用户一些事情，你想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，您至少要询问一次，它通常比使用 while 更优雅，后者需要复制代码，或添加额外条件或设置任意值第一次强制进入循环.

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，while 循环更为常见，可以轻松替换 do-while(并非所有语言都有这两种循环).

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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