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Array Iteration with a For Loop
6:27Use a for loop to both build an array and iterate through every element in an array.
For this project, you had to create
a function to build an array
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of ten random numbers between one and 100.
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Then you had to call that function
to create an array, then use a for
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loop to access each item in that array.
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Now, we provided the function for
the random number generator.
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If you want to brush up on
the Math.random function,
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check out the teacher's notes for links.
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Let's start by creating
the shell of the function, and
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we'll name that function createRandomList.
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I'll type function createRandomList,
a set of parentheses, and a set of braces.
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Now I'll start by creating an empty
array to hold the random numbers.
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I'll call it randomList.
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In order to add ten random
numbers to the list,
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I'll create a loop that runs ten times and
uses a counter variable named i.
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Now each time through the loop,
the i counter increments by one.
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That's this i+=1 part.
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Now a shorter way to
write that is just i++.
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++ is an incremental operator,
and just adds 1 to the variable.
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Now, if you're bit rusty on for
loops, see the teachers notes, for
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a link to more instruction on them.
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Now within the loop,
I'll call the random 100 function, and
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store the results into a temporary
variable called randomNumber.
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Then to add the number to the randomList
array, just use the array push method,
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like this.
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Type the array name, randomList.push,
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and then I pass randomNumber,
that's the variable.
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Now you could actually
simplify this code a bit,
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you don't need this
randomNumber variable at all.
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It simply holds a value,
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the same value that's returned when
the randomNumber function is called.
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You can skip the variable, and
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simply call the randomNumber
function like this.
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Now outside the loop, we want to return
the ten item random list variable.
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Let's try out this
function by calling it and
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storing the results into a new
variable named myRandomList.
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Type let myRandomList =
createRandomList() with
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a set of parentheses to call the function.
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To see if it worked,
let's log the array to the console.
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I'll type console.log(myRandomList).
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Let's save the file.
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And use node to run it in the console,
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by typing node 2_loop.js.
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And there you have a ten item array.
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How do we know that they're random?
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Well, let me call it again and let's see
if we get different numbers, and we do.
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If your program isn't working, double
check against the code in the teacher's
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notes below and
try to figure out your error.
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Now, the last part of this project is
to use a for loop to iterate through
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the array and print the elements
one line at a time to the console.
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First, I'll add the basic format for
a for loop.
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Now, this loop will run ten times.
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That's fine in this particular case
because the array has ten items, but
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it's not very flexible.
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It'd be better to run this loop
the same number of times as there
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are elements in the array.
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Fortunately, we can get the number of
items in an array using an array's
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length property.
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So just replace 10 here
with myRandomList.length.
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Okay, let's log a string to the console.
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Inside the loop, I'm just gonna
type console.log to begin with.
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Let's just print out a simple string,
Item 0 in the array is 48.
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Let's see what happens,
I'm gonna save this file.
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Clear my console and
run the program again.
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Well, [LAUGH] that isn't very helpful
cuz it prints the exact same string
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over and over again.
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So let's make this a little bit
more tailored to our array.
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So I'm gonna change this 0,
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and using string concatenation,
I'll add our i counter.
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Let's see what happens now.
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A little bit better.
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So we see the index increasing,
0, 1, 2, 3.
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But we're always getting the same number.
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So what we need to do now
is access the element
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at the same index value within the array.
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And we can use the i counter to do that.
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Use string concatenation one more time
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to access myRandomList
at the i index value.
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Let's save this file, Type clear,
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And run this one more time,
and there it is.
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If you had trouble with this
practice session, don't worry.
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Compare your code to the code listed
in the teacher's notes below.
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Look very carefully at
what tripped you up.
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Study it and
figure out how to fix your code.
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Failure is the best way to learn, and
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we don't usually get things
right on the first try.
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As you'll learn later, there are other
array methods that can help you achieve
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similar results, like the for each method.
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As always in programming,
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there are often many different
ways to solve the same problem.
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Ready for the final practice challenge?
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I’ll see you in the next video.
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