PLC编程中，循环语句FOR和WHILE怎么选？

<p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">迭代语句主要用于重复执行的程序，在 CoDeSys 中，常见的迭代语句有 FOR，REPEAT 及WHILE 语句。</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);">FOR 循环</p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">FOR 循环语句用于计算一个初始化序列，当某个条件为 TRUE 时，重复执行嵌套语句并计算一个迭代表达式序列，如果为 FALSE，则终止循环，具体格式如下。</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">FOR &lt;变量&gt; := &lt;初始值&gt; TO &lt;目标值&gt; {BY &lt;步长&gt;} DO</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">&lt;语句内容&gt;</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">END_FOR</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">FOR 循环的执行顺序如下：</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;"> 计算&lt;变量&gt;是否在&lt;初始值&gt;与&lt;目标值&gt;的范围内；</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;"> 当&lt;变量&gt;小于&lt;目标值&gt;，执行&lt;语句内容&gt;；</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;"> 当&lt;变量&gt;大于&lt;目标值&gt;，则不会执行&lt;语句内容&gt;；</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;"> 当每次执行&lt;语句内容&gt;时，&lt;变量&gt;总是按照指定的步长增加其值。步长可以是任意的整数值。</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;"><span style="border: 0px; margin: 0px; padding: 0px;">如果不指定步长，则其缺省值是 1</span>。当&lt;变量&gt;大于&lt;目标值&gt;时，退出循环。</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;"><span style="font-weight: 700; border: 0px; margin: 0px; padding: 0px;">示例：</span>使用 FOR 循环实现 2 的五次方计算。</span></p><p><img src="/upload/image/20230616/1686877433264106.jpeg"/></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">假设 Var1 的初始值是 1，那么循环结束后，Var1的值的为 32。</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);">WHILE 循环</p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">WHILE 循环与 FOR 循环使用方法类似。二者的不同之处是，WHILE 循环的结束条件可以是任意的逻辑表达式。即可以指定一个条件，当满足该条件时，执行循环，具体格式如下。</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">WHILE &lt;布尔表达式&gt;</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">&lt;语句内容&gt;</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">END_WHILE</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">WHILE 循环的执行顺序如下：</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;"> 计算&lt;布尔表达式&gt;的返回值。</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;"> 当&lt;布尔表达式&gt;的值为 TRUE 时，重复执行&lt;语句内容&gt;。</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;"> 当&lt;布尔表达式&gt;初始值为 FALSE，那么指令&lt;语句内容&gt;不会被执行，跳转至 WHILE 语句的结尾。</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><img src="/upload/image/20230616/1686877452825919.jpeg" style="border: 0px; margin: 10px auto 0px; padding: 0px; display: block; height: auto;"/></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">注意：</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">如果&lt;布尔表达式&gt;的值始终为 TRUE，那么将会产生死循环，应当避免死循环的产生。可以通过改变循环指令的条件来避免死循环的产生。例如：利用可增减的计数器避免死循环的产生。</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;"><span style="font-weight: 700; border: 0px; margin: 0px; padding: 0px;">示例：</span>只要计数器不为零，则始终执行循环体内的程序。</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><img src="/upload/image/20230616/1686877453925921.jpeg" style="border: 0px; margin: 10px auto 0px; padding: 0px; display: block; height: auto;"/></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">在一定的意义上，WHILE 循环比 FOR 循环的功能更加强大，这是因为在执行循环之前，</span></p><p style="border: 0px; margin-top: 0.63em; margin-bottom: 1.8em; padding: 0px; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; color: rgb(25, 25, 25); font-family: &quot;PingFang SC&quot;, Arial, 微软雅黑, 宋体, simsun, sans-serif; text-wrap: wrap; background-color: rgb(255, 255, 255);"><span style="border: 0px; margin: 0px; padding: 0px;">WHILE 循环不需要知道循环的次数。因此，如果清楚地知道了循环的次数，那么 FOR 循环更好，因为 FOR 循环可以避免产生死循环。</span></p><p><br/></p>