A for loop with different input values

Assuming this is to iterate over an array with variable start and end.

1. Get the start index form the array
2. Get the end index from the array
3. Adjust the end if it is smaller than start, add in this case array.length
4. Iterate over the new start and end indices
5. Adjust the index, because it can runs outside the array.length with the remainder operator.

var array = [1, 2, 3, 4, 5, 6, 7],
    startday = 5,
    endday = 1,
    k,
    start = array.indexOf(startday),
    end = array.indexOf(endday);

if (end < start) {
    end += array.length;
}
for (var k = start; k <= end; k++ ){
    document.write(array[k % array.length] + '<br>');
}

You should use --k as third parameter of for (it causes k variable to be decremented)

var array = [1,2,3,4,5,6,7];
var startday=5;
var endday=1
for (var k=startday; k >= endday; --k)
{
}

inside your loop, print this 'array[k]' , and 'if(k > array.length){ print 1 and break}'

Does it have to be a for loop? How about this:

var array = [1,2,3,4,5,6,7];
var startday = 5;
var endday = 1;
var k = startday;
while (k > endday){
    // print array[k-1]

    if (k == array.length){
        k = 1;
    } else {
        k++;
    }
}
while (k <= endday){
    // print array[k-1]

    k++;
}

I'm assuming startday and endday refer to an array index.

Try this

<script src="http://code.jquery.com/jquery.min.js"></script>
<script type="text/javascript">
var array = [11,22,33,44,55,66,77];

var startday=55;
var endday=11;

var lastEl = array[array.length-1];
var index_startday =  $.inArray( startday, array );

 for(var count=index_startday; count <= array.length;count++){
    alert(array[count]);
    if(array[count] == endday){
        break;
    }
    if(array[count] == lastEl){
      count = -1;
      continue;
    }
   }
</script>