// for loop
for(var i = 1; i <= n; i++){

}

// foreach loop
// used to read item from IEnumerable  / IEnumerable <T>  (to manipulate items use for loop or iterator)
var items = new int[] { 1, 2, 3, 5, 8};
foreach (var item in items){

}

// while loop
while(node != null){
    // ... ... ...
    node = node.Next;
}