Beginner question - why should I use nested loop in this example? - swift

Question

I’m trying to learn Swift. I’m now on lesson 5 of “Swift Tutorial for Beginners” by Code with Chris. I’m finishing all the challenges he prepared, but I’m stuck at Challenge 5, which is to print a pattern like this:
*
**
***
****
*****
I don’t get why should I use nested loop.
According to the completed challenge file, the code should look like this:
var drawPixel:String = "*"
var height:Int = 5
var tempRow:String = ""
for columnPixel in 1...height {
tempRow = ""
for _ in 1...columnPixel{
tempRow += drawPixel
}
print(tempRow)
}
but
var drawPixel:String = "*"
var height:Int = 5
var tempRow:String = ""
for _ in 1...height{
tempRow += drawPixel
print(tempRow)
}
also works the way it should and seems way simplier. I understand my method (second code), but not the one I’m supposed to use. My questions:
Why is there a nested loop?
why in first example nested loop refers to columnPixel (for _ in 1...columnPixel) since it is already defined that it should repeat the loop to 5?
Lastly, why "print(tempRow)" is outside of a nested loop?
Here's the challenge: https://docs.google.com/document/d/1DI-4RkYkRl8EPY17TOwfK8gCl--KMdqLEPP-hz6QHI0/edit# (scrool down to Challenge 5)
Thank you in advance!

Answer 1

Why is there a nested loop?
The outer loop and inner loop serve different purposes. Each iteration of the outer loop prints one row. Each iteration of the inner loop "constructs" the string that is printed.
why in first example nested loop refers to columnPixel (for _ in 1...columnPixel) since it is already defined that it should repeat the loop to 5?
columnPixel is referred in the inner loop because the number of iterations of the inner loop changes depending on which iteration of the outer loop:
In the first iteration of the outer loop, the inner loop loops only once. The string constructed is *
In the second iteration of the outer loop, the inner loop loops twice. The string constructed is **
In the third iteration of the outer loop, the inner loop loops three times. The string constructed is ***
and so on...
Notice that columnPixel changes with each iteration of the outer loop. In the first iteration it's 1, in the second iteration it's 2, etc. This is why we say "loop columnPixel lots of times" in the inner loop.
Lastly, why "print(tempRow)" is outside of a nested loop?
We only want to print the constructed string, not while we are constructing it.