How to set 2 different classes by if else condtion in foreach loop with predefined order?

Suppose I have 10 records, and 2 different classes namely c1, c2

 <div class="c2">..content..</div>
<div class="c2">..content..</div>
<div class="c1">..content..</div>
<div class="c1">..content..</div>
<div class="c2">..content..</div>
<div class="c2">..content..</div>
<div class="c1">..content..</div>
<div class="c1">..content..</div>
<div class="c2">..content..</div>
<div class="c2">..content..</div>

i want the if else condition where class order needs to maintained like c2,c2,c1,c1,c2,c2,c1,c1,c2,c2.....so on

foreach(x as y){ 
if() {
   <div class="<?php echo $class1;?>">..content..</div>
} else { 
 <div class="<?php echo $class2;?>">..content..</div>
}

class order should be c2,c2,c1,c1,c2,c2,c1,c1,c2,c2.....so on

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