Let’s hit arrays with loops!

Loops and arrays are closely related. For many operations with arrays, for example, counting sums of elements, loops are used. Now you are ready to use a loop to bypass the array.

Loop for will be the best for this task. The loop variable will be used as an index of array elements. Therefore, let’s assign it a zero value and increase it by one at each iteration until its value becomes equal to the index of the last element.

The traditional name for the loop variable i is an abbreviation of index, that is, an index or a serial number. This is also one of the agreements among programmers, which allows us to shorten the code.

And one more style-related detail. What is the best way to write the exit condition for the loop? There are two options. Let’s analyze then using an example of an array of three elements:

// First option: i < usersByDay.length
// usersByDay.length == 3

Preparation: i = 0
1 iteration: i = 0; 0 < 3? yes! first iteration actions; i = 1
2 iteration: i = 1; 1 < 3? yes! second iteration actions; i = 2
3 iteration: i = 2; 2 < 3? yes! third iteration actions; i = 3
4 iteration: i = 3; 3 < 3? no! Finish the loop!

// Second option: i <= usersByDay.length - 1
// usersByDay.length - 1 == 2

Preparation: i = 0
1 iteration: i = 0; 0 <= 2? yes! first iteration actions; i = 1
2 iteration: i = 1; 1 <= 2? yes! second iteration actions; i = 2
3 iteration: i = 2; 2 <= 2? yes! third iteration actions; i = 3
4 iteration: i = 3; 3 <= 2? no! Finishing the loop!

Both exit conditions options, i < usersByDay.length and i <= usersByDay.length - 1, work the same way. But for now we will use the second option, subtracting one. It will remind us of the unusual numbering of array elements that starts from zero.