logging current array value to console...stuck

The .length property tells you how many items are currently in an array. In your case, temperatures.length = 8, since there are 8 items (100,90,99,80,70,65,30,10) in the temperatures array.

I've corrected your code to:

var temperatures = [100,90,99,80,70,65,30,10];

for ( var i = 0; i < temperatures.length; i += 1 ) {
    console.log (temperatures[i]);
}

Your code didn't run, because you set i = 10. In your code block however, you use console.log(array[i]). array[i] accesses a value at a certain index in an array.

So in order to be able to iterate through the array, you need to set var i = 0, to be able to start with the value at the zero index (meaning the first position in your array).

An overview of index and value in your array:

index 0 is value 100, index 1 is value 90, index 2 is value 99, index 3 is value 80, index 4 is value 70, index 5 is value 65, index 6 is value 30, index 7 is value 10.

With i = 0, you set array[i] to array[0], and you are then looking at the value at the zero index in your array (which is 100). If you use array[i] in console.log you will then print every value of the array into the console, with i = 0 being 100, i = 1 being 90 etc.

I hope this helps. :)

Matthijs Boet 's answer was left as a comment instead of an "answer".

So you can more easily find it (or others if looking for this question with an answer), here is his response:

It can by useful if you want to know how many times you have to iterate over an array to loop over each item.

const temperatures = [100, 90 ,99 ,80 ,70 ,65 ,30 ,10]; 
for (let i= 0; i < temperatures.length; i +=1 ) {
console.log (temperatures[i]);
}

Try this and it will print out the array index number after the array element

{
    console.log(temperatures[i], i);
}
100 0
90 1
99 2
80 3
70 4
65 5
30 6
10 7