# FAQ: Loops - Review

This community-built FAQ covers the “Review” exercise from the lesson “Loops”.

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This exercise can be found in the following Codecademy content:

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I can do this in Python easily but can’t figure out the best way to do this in Swift. Any help?

star = “*”

for num in range(1,5):
starCount = “*” * num
print(starCount)

@microsolver41079

from the codecademy class earlier, they syntax for range is three dots
in order to print 4 lines I wrote:
in 1…4

so full thing
var star = “*”

for _ in 1…4 {
print(star)
star += “*”
}

check out Swift class on codecademy, you will find more.

1 Like

I ended up combining 1st and 2nd exercise.
Is there a simpler way to determine odd and even numbers with prime marker?
I wonder if so many “if” is necessary or the sequence should be different to make it simpler.

//program for odd and even numbers with prime indicator
for num in 1…100 {
if num % 2 == 0 && num > 2 {
print("(num) is even")
} else if num == 1 || num % 3 == 0 && num > 3 || num % 5 == 0 && num > 5 || num % 7 == 0 && num > 7 {
print("(num) is odd")
} else if num == 2 {
print("(num) is even and prime number")
}else {
print("(num) is odd and prime number")
// div 1 and self
}
}

As for the second challenge,

why do we need “-1” (minus one) in this line of code?

for num in 2…checkPrime - 1 {

Thanks!

// Second Challenge
// checkPrime can be changed to a positive number greater than 1
var checkPrime = 17
// Assume the number is prime until proven otherwise
var isPrime = true
for num in 2…checkPrime - 1 {
// If checkPrime is fully divisible by the current number it’s not a prime number
if checkPrime % num == 0 {
isPrime = false
break
}
}

You are referring to the github code solution linked to by Codecademy for the challenge. As mentioned in the hints “Prime numbers are only divisible by 1 and themselves”. In the github code snippet, checkPrime is the candidate integer that we want to check for being a prime. Subtracting 1 from this number helps us avoid the “and themselves” division, because every number (prime or composite) is divisible by itself. e.g. Suppose we want to check whether 15 is a prime number or not, then we shouldn’t check whether 15 divides 15 perfectly. Instead, we just need to ensure that none of the numbers 2 through 14 (one less than 15) divides 15 perfectly. As soon as one of these numbers divides 15 perfectly, we can stop immediately.