Stride for custom step in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of stride with positive step

What is the output of this Swift code using stride with a positive step?

Swift

for number in stride(from: 2, to: 10, by: 3) {
    print(number, terminator: " ")
}

A 2 5 8

B 2 3 4 5 6 7 8 9

C 2 6 10

D 3 6 9

💡 Hint

Remember that 'to' excludes the upper bound and the step is 3.

The stride starts at 2 and adds 3 each time: 2, 5, 8. It stops before reaching 10.

❓ Predict Output

intermediate

Output of stride with negative step

What is the output of this Swift code using stride with a negative step?

Swift

for number in stride(from: 10, through: 2, by: -4) {
    print(number, terminator: " ")
}

A 10 6 2

B 10 6

C 10 8 6 4 2

D 10 2

💡 Hint

The 'through' keyword includes the end value, and step is negative.

Starting at 10, subtract 4 each time: 10, 6, 2. The loop includes 2 because of 'through'.

🧠 Conceptual

advanced

Behavior of stride with zero step

What happens if you use stride(from: 1, to: 10, by: 0) in Swift?

A The loop does not run at all.

B The program runs an infinite loop printing 1 endlessly.

C The program throws a runtime error due to zero step.

D The loop runs once printing 1 and stops.

💡 Hint

Think about what happens when the step never changes the value.

A zero step causes a runtime error because the step must not be zero.

❓ Predict Output

advanced

Count of elements generated by stride

How many numbers does this Swift stride generate?

Swift

let numbers = Array(stride(from: 0, to: 20, by: 7))
print(numbers.count)

A 4

B 3

C 2

D 5

💡 Hint

Count the numbers starting at 0, adding 7 each time, stopping before 20.

The numbers are 0, 7, 14. The next would be 21 which is beyond 20, so count is 3.

❓ Predict Output

expert

Output of stride with floating point step

What is the output of this Swift code using stride with a floating point step?

Swift

for value in stride(from: 0.0, through: 1.0, by: 0.3) {
    print(String(format: "%.1f", value), terminator: " ")
}

A 0.0 0.3 0.6 0.9 1.2

B 0.0 0.3 0.6 0.9 1.1

C 0.0 0.3 0.6 0.9 1.0

D 0.0 0.3 0.6 0.9

💡 Hint

'through' includes the end value only if exactly reachable by the steps; consider floating-point.

The stride generates 0.0, 0.3, 0.6, 0.9. The next value 1.2 exceeds 1.0, and 1.0 is not exactly reached.

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