For-in loop with ranges in Swift - Mini Project: Build & Apply

For-in loop with ranges

📖 Scenario: You are helping a small bakery count the number of cupcakes they bake each day for a week. They want to know the total cupcakes baked from Monday to Sunday.

🎯 Goal: Build a Swift program that uses a for-in loop with a range to sum the cupcakes baked each day and print the total.

📋 What You'll Learn

Create a dictionary called cupcakesBaked with keys as days of the week and values as the number of cupcakes baked.

Create a constant days that holds the range from 1 to 7 representing days Monday to Sunday.

Use a for-in loop with the variable day to iterate over days.

Inside the loop, add the cupcakes baked for each day to a variable totalCupcakes.

Print the total cupcakes baked after the loop.

💡 Why This Matters

🌍 Real World

Counting daily production or sales is common in small businesses to track performance and plan inventory.

💼 Career

Using loops and ranges to process data collections is a fundamental skill for software developers, especially in data processing and automation tasks.

1

Create the cupcakes data

Create a dictionary called cupcakesBaked with these exact entries: 1: 12, 2: 15, 3: 10, 4: 20, 5: 18, 6: 25, 7: 22.

Swift

# Create the cupcakesBaked dictionary with days 1 to 7 and their cupcake counts
# Your code here

Hint

Use a Swift dictionary with integer keys for days and integer values for cupcakes.

2

Create the days range

Create a constant called days that holds the range from 1 to 7 inclusive.

Swift

let cupcakesBaked = [1: 12, 2: 15, 3: 10, 4: 20, 5: 18, 6: 25, 7: 22]
# Create the days range from 1 to 7
# Your code here

Hint

Use the closed range operator ... to include both 1 and 7.

3

Sum cupcakes using a for-in loop

Create a variable called totalCupcakes and set it to 0. Then use a for-in loop with the variable day to iterate over days. Inside the loop, add the cupcakes baked for each day from cupcakesBaked to totalCupcakes. Use optional unwrapping with ?? 0 to handle missing values.

Swift

let cupcakesBaked = [1: 12, 2: 15, 3: 10, 4: 20, 5: 18, 6: 25, 7: 22]
let days = 1...7
# Create totalCupcakes variable and sum cupcakes in a for-in loop
# Your code here

Hint

Remember to initialize totalCupcakes before the loop and use cupcakesBaked[day] ?? 0 to safely get the value.

4

Print the total cupcakes

Write a print statement to display the text Total cupcakes baked: followed by the value of totalCupcakes using string interpolation.

Swift

let cupcakesBaked = [1: 12, 2: 15, 3: 10, 4: 20, 5: 18, 6: 25, 7: 22]
let days = 1...7
var totalCupcakes = 0
for day in days {
    totalCupcakes += cupcakesBaked[day] ?? 0
}
# Print the total cupcakes baked
# Your code here

Hint

Use print("Total cupcakes baked: \(totalCupcakes)") to show the result.

Practice

1. What does the following Swift code print?
for i in 1...3 { print(i) }

easy

A. 1 2

B. 1 2 3

C. 0 1 2 3

D. 2 3 4

Solution

1. Step 1: Understand the range operator

   The range 1...3 is a closed range including 1, 2, and 3.

2. Step 2: Loop prints each number in the range

   The loop prints 1, then 2, then 3 on separate lines.

3. Final Answer:

   1 2 3 -> Option B

4. Quick Check:

   Closed range includes last number = 1 2 3 [OK]

Hint: Closed range includes last number, so count all numbers [OK]

Common Mistakes:

• Thinking the last number is excluded
• Starting from 0 instead of 1
• Confusing closed and half-open ranges

2. Which of the following is the correct syntax for a for-in loop iterating from 0 to 4 (excluding 4) in Swift?

easy

A. for i in 0...4 { }

B. for i in 0 to 4 { }

C. for i in 0..<4 { }

D. for i = 0; i < 4; i++ { }

Solution

1. Step 1: Identify the correct range syntax

   0..<4 is a half-open range including 0,1,2,3 but excluding 4.

2. Step 2: Check Swift for-in loop syntax

   Swift uses 'for variable in range { }' syntax; 'for i in 0..<4 { }' is correct.

3. Final Answer:

   for i in 0..<4 { } -> Option C

4. Quick Check:

   Half-open range excludes last number = for i in 0..<4 { } [OK]

Hint: Use '..<' for half-open range excluding last number [OK]

Common Mistakes:

• Using '...' when last number should be excluded
• Using 'to' keyword which is invalid in Swift
• Using C-style for loop syntax which is not valid in Swift

3. What is the output of this Swift code?

var sum = 0
for number in 1..<5 {
  sum += number
}
print(sum)

medium

A. 10

B. 15

C. 14

D. Error

Solution

1. Step 1: Identify the range and loop values

   The range 1..<5 includes 1, 2, 3, 4 (excluding 5).

2. Step 2: Calculate the sum of these numbers

   Sum = 1 + 2 + 3 + 4 = 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   Sum of 1 to 4 = 10 [OK]

Hint: Half-open range excludes last number; sum 1+2+3+4 = 10 [OK]

Common Mistakes:

• Including 5 in the sum
• Adding numbers incorrectly
• Confusing closed and half-open ranges

4. The following Swift code has an error. What is it?

for i in 1..< { print(i) }

medium

A. No error, code runs fine

B. Using wrong loop variable

C. Using closed range instead of half-open

D. Missing end value in range

Solution

1. Step 1: Check the range syntax

   The range 1..< is incomplete; it misses the end value after '..<' operator.

2. Step 2: Identify the error type

   This causes a syntax error because Swift expects a number after '..<' to define the range.

3. Final Answer:

   Missing end value in range -> Option D

4. Quick Check:

   Range must have start and end values [OK]

Hint: Range must have start and end values, '..<' alone is invalid [OK]

Common Mistakes:

• Leaving out the end value in range
• Confusing '..<' with '...' syntax
• Assuming loop variable causes error

5. You want to print all even numbers from 2 to 10 inclusive using a for-in loop with a range. Which code correctly does this?

hard

A. for i in 2...10 where i % 2 == 0 { print(i) }

B. for i in 2..<10 { if i % 2 == 0 { print(i) } }

C. for i in 2...10 { if i % 2 == 1 { print(i) } }

D. for i in 2...9 where i % 2 == 0 { print(i) }

Solution

1. Step 1: Understand the range and condition

   We want even numbers from 2 to 10 inclusive, so use closed range 2...10.

2. Step 2: Use 'where' clause to filter even numbers

   The 'where i % 2 == 0' filters only even numbers in the loop.

3. Final Answer:

   for i in 2...10 where i % 2 == 0 { print(i) } -> Option A

4. Quick Check:

   Closed range + where filter = for i in 2...10 where i % 2 == 0 { print(i) } [OK]

Hint: Use closed range and 'where' to filter even numbers [OK]

Common Mistakes:

• Using half-open range excluding 10
• Printing odd numbers by mistake
• Forgetting to filter even numbers