Stride for custom step in Swift

Introduction

Stride lets you count numbers with a custom step size easily. It helps when you want to skip numbers or count in jumps.

When you want to count every 2 or 3 numbers instead of every single number.

When you need to loop through a range but only want certain steps, like every 5 minutes in a clock.

When you want to create a sequence of numbers that increase or decrease by a fixed amount.

When you want to avoid writing manual math to jump steps in a loop.

Syntax

Swift

stride(from: start, to: end, by: step)
stride(from: start, through: end, by: step)

from is where counting starts.

to stops before this number, through includes this number.

Examples

Counts from 0 up to but not including 10, stepping by 2.

Swift

for number in stride(from: 0, to: 10, by: 2) {
    print(number)
}

Counts from 1 up to and including 5, stepping by 1.

Swift

for number in stride(from: 1, through: 5, by: 1) {
    print(number)
}

Counts down from 10 to just above 0, stepping down by 3.

Swift

for number in stride(from: 10, to: 0, by: -3) {
    print(number)
}

Sample Program

This program shows counting up from 0 to 15 by 3 steps, then counting down from 20 to 0 by 4 steps.

Swift

import Foundation

print("Counting up by 3:")
for number in stride(from: 0, to: 15, by: 3) {
    print(number)
}

print("Counting down by 4:")
for number in stride(from: 20, through: 0, by: -4) {
    print(number)
}

Important Notes

Use to when you want to stop before the end number.

Use through when you want to include the end number.

Negative by values let you count backwards.

Summary

Stride helps count numbers with custom steps easily.

Use to to exclude the end, through to include it.

Steps can be positive or negative for counting up or down.

Practice

1. What does the Swift function stride(from: 1, to: 10, by: 2) do?

easy

A. Generates numbers starting at 1, decreasing by 2, up to but not including 10.

B. Generates numbers starting at 1, increasing by 2, including 10.

C. Generates numbers starting at 1, increasing by 2, up to but not including 10.

D. Generates numbers starting at 1, decreasing by 2, including 10.

Solution

1. Step 1: Understand the parameters of stride

   The function uses from: 1 as the start, to: 10 as the end (exclusive), and by: 2 as the step size.

2. Step 2: Determine the sequence generated

   It generates numbers starting at 1, adding 2 each time, stopping before reaching 10, so the sequence is 1, 3, 5, 7, 9.

3. Final Answer:

   Generates numbers starting at 1, increasing by 2, up to but not including 10. -> Option C

4. Quick Check:

   stride(from:1, to:10, by:2) excludes 10 [OK]

Hint: Remember: 'to' excludes the end value in stride [OK]

Common Mistakes:

• Confusing 'to' with 'through' and including the end value
• Mixing up positive and negative step directions
• Assuming the step is always 1

2. Which of the following is the correct syntax to create a stride in Swift that counts down from 10 to 2 by steps of 2, including 2?

easy

A. stride(from: 10, through: 2, by: -2)

B. stride(from: 10, to: 2, by: -2)

C. stride(from: 2, through: 10, by: 2)

D. stride(from: 2, to: 10, by: 2)

Solution

1. Step 1: Identify counting down with inclusion

   Counting down from 10 to 2 means the step is negative (-2). Including 2 means using through.

2. Step 2: Match syntax to requirements

   Only stride(from: 10, through: 2, by: -2) matches counting down with inclusion of 2.

3. Final Answer:

   stride(from: 10, through: 2, by: -2) -> Option A

4. Quick Check:

   Use 'through' to include end, negative step for countdown [OK]

Hint: Use 'through' to include end; negative step for countdown [OK]

Common Mistakes:

• Using 'to' instead of 'through' when including the end
• Using positive step when counting down
• Swapping start and end values

3. What is the output of the following Swift code?

for i in stride(from: 0, to: 5, by: 2) {
    print(i)
}

medium

A. 0 2 4

B. 0 2 4 6

C. 0 2 4 5

D. 2 4

Solution

1. Step 1: Analyze the stride parameters

   The loop starts at 0, goes up to but excludes 5, stepping by 2.

2. Step 2: List the values printed

   Values are 0, 2, 4. It stops before reaching 5.

3. Final Answer:

   0 2 4 -> Option A

4. Quick Check:

   Stride 'to' excludes end, so 5 is not printed [OK]

Hint: Remember 'to' excludes end value in stride loops [OK]

Common Mistakes:

• Including the end value 5 mistakenly
• Adding an extra step beyond the end
• Confusing step size with end value

4. Identify the error in this Swift code snippet:

for i in stride(from: 1, through: 10, by: 0) {
    print(i)
}

medium

A. Using 'through' instead of 'to' is invalid syntax.

B. Step value cannot be zero; it causes a runtime error.

C. Start value must be less than end value for positive step.

D. The loop will run infinitely without errors.

Solution

1. Step 1: Check the step parameter

   The step is zero, which is invalid because it causes no progress in the loop.

2. Step 2: Understand the effect of zero step

   A zero step causes a runtime error or infinite loop because the loop never advances.

3. Final Answer:

   Step value cannot be zero; it causes a runtime error. -> Option B

4. Quick Check:

   Step must not be zero in stride [OK]

Hint: Step cannot be zero; always non-zero positive or negative [OK]

Common Mistakes:

• Thinking 'through' is invalid syntax
• Assuming zero step means step of 1
• Ignoring runtime errors caused by zero step

5. You want to create a Swift loop that prints all odd numbers from 1 to 15 inclusive, but only those greater than 5. Which stride and condition combination achieves this?

hard

A. for i in stride(from: 1, to: 15, by: 2) { if i >= 5 { print(i) } }

B. for i in stride(from: 5, to: 15, by: 2) { print(i) }

C. for i in stride(from: 1, through: 15, by: 2) { if i >= 5 { print(i) } }

D. for i in stride(from: 1, through: 15, by: 2) { if i > 5 { print(i) } }

Solution

1. Step 1: Identify stride to generate odd numbers 1 to 15 inclusive

   Using stride(from: 1, through: 15, by: 2) generates 1,3,5,...,15 including 15.

2. Step 2: Filter numbers greater than 5

   The condition if i > 5 prints only numbers greater than 5, i.e., 7,9,11,13,15.

3. Final Answer:

   for i in stride(from: 1, through: 15, by: 2) { if i > 5 { print(i) } } -> Option D

4. Quick Check:

   Stride with 'through' includes 15; condition filters >5 [OK]

Hint: Use 'through' to include end; filter inside loop for conditions [OK]

Common Mistakes:

• Using 'to' excludes 15, missing last number
• Incorrect condition filtering numbers equal to 5
• Starting stride at 5 misses odd numbers less than 5