Solving a nested loop question in Swift Programming: The Big Nerd Ranch Guide

Question

I am new to learning Swift and am trying to solve a challenge in Swift Programming: The Big Nerd Ranch Guide (1st Ed.). The question is in Chapter 6 about using a nested loop:

Use a loop to count by 2 from 0 to 100. Use another loop to make sure the first loop is run 5 times. Hint: one good way to do this is to use a nested loop.

I think I've found the answers but a bit unsure, any advise would be much appreciated!

for i in 1...5 {
    for i in 0...100 {
        if i % 2 == 0 {
            print(i)
        }
    }
}

I would avoid using the same index variable, i, for both loops. That is confusing. — Duncan C
– Duncan C, Commented Sep 22, 2018 at 11:34
@Carpsen90: Not that I would recommend it, but you can have nested loops with the same name for the loop variable, the inner i then simply shadows the outer i. — Martin R
– Martin R, Commented Sep 22, 2018 at 12:16
@Carpsen90 Because the question asks for the counts to be repeated 5 times so I thought the solution would be to nest the loop inside another that will make it run 5 times. — delb99
– delb99, Commented Sep 22, 2018 at 12:37
@delb99 If the goal is count from 0 to 100, using nested loops, with the outside loop running 5 times, then see my answer. If you want to count from 0 to a 100 five times then your code already works and you should take the comments from Duncan and Martin into consideration. — ielyamani
– ielyamani, Commented Sep 22, 2018 at 12:42

vadian · Accepted Answer · 2018-09-22 09:58:02Z

2

Basically the solution is correct. However in Swift there are two more efficient syntaxes

Filter with where

for _ in 1...5 {
    for i in 0...100 where i % 2 == 0 {
        print(i)
    }
}

Loop with stride (recommended)

for _ in 1...5 {
    for i in stride(from: 0, through: 100, by: 2) {
        print(i)
    }
}

As the outer index variable is not used follow the replacing with '_' suggestion in the warning

answered Sep 22, 2018 at 9:58

vadian

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2 Comments

Duncan C Over a year ago

I haven't seen the where qualifier on a for loop before. Where did you learn that? (Voted)

vadian Over a year ago

@DuncanC It's listed in Swift - Summary of the Grammar. The where clause is a common pattern in Swift. It can be used in for loops, switch cases, generics and as type constraint operator.

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