Why is the len ( ) function useful when using a loop to iterate through a stack?
the len ( ) function will print the elements of the stack.
the len ( ) function will run with each iteration, printing the element number each time.
the len ( ) function will tell the program the number of elements in the stack.
the len ( ) function will remove the duplicate elements in the stack.

The len ( ) function will tell the program the number of elements in the stack.

Explanation:

I'll assume it's in Python, since you also asked another question that is in Python.

Why is the len ( ) function useful when using a loop to iterate through a stack?

The len() function returns the count of the items it's passed. If it's a stack of elements, it will return the number of elements.

The len() function does NOT print or remove items from the collection it received. So, that eliminates all other answer options you have listed (2 have prints and one has remove).  If the value of len() is printed, it's through another function outputting the value returned by len(), not len() itself.

answer///copyrights protects;