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

For loop with ranges

📖 Scenario: You are helping a small bakery count how many cupcakes they have baked each day over a week.

🎯 Goal: Build a Kotlin program that uses a for loop with a range to count cupcakes baked from day 1 to day 7.

📋 What You'll Learn

Create a variable called totalCupcakes and set it to 0

Create a for loop using day in the range 1 to 7

Inside the loop, add 10 cupcakes for each day to totalCupcakes

Print the final value of totalCupcakes

💡 Why This Matters

🌍 Real World

Counting items or events over a fixed number of days or steps is common in business and daily life.

💼 Career

Understanding loops and ranges helps automate repetitive tasks and process data efficiently in software development.

1

Create the initial variable

Create a variable called totalCupcakes and set it to 0.

Kotlin

var totalCupcakes = 0
// Your code here

Hint

Use var to create a variable that can change.

2

Set up the for loop with range

Create a for loop with variable day that goes from 1 to 7 using a range.

Kotlin

var totalCupcakes = 0
for (day in 1..7) {
    // Your code here
}

Hint

Use 1..7 to create a range from 1 to 7 inclusive.

3

Add cupcakes inside the loop

Inside the for loop, add 10 to totalCupcakes for each day.

Kotlin

var totalCupcakes = 0
for (day in 1..7) {
    totalCupcakes += 10
    // Your code here
}

Hint

Use += to add to the existing value of totalCupcakes.

4

Print the total cupcakes

Write a println statement to print the value of totalCupcakes.

Kotlin

var totalCupcakes = 0
for (day in 1..7) {
    totalCupcakes += 10
}
// Your code here

Hint

Use println(totalCupcakes) to show the total cupcakes baked.

Practice

1. What does the following Kotlin code do?
for (i in 1..5) { println(i) }

easy

A. Prints numbers from 1 to 4

B. Prints numbers from 1 to 5 inclusive

C. Prints numbers from 0 to 5

D. Prints numbers from 5 down to 1

Solution

1. Step 1: Understand the range operator

   The operator 1..5 creates a range including numbers 1, 2, 3, 4, and 5.

2. Step 2: Loop through the range

   The for loop runs from 1 to 5, printing each number.

3. Final Answer:

   Prints numbers from 1 to 5 inclusive -> Option B

4. Quick Check:

   Range 1..5 includes 5 [OK]

Hint: .. means inclusive range from start to end [OK]

Common Mistakes:

• Thinking .. excludes the last number
• Confusing range with step or downTo
• Assuming it counts down automatically

2. Which of the following is the correct syntax for a for loop counting down from 5 to 1 in Kotlin?

easy

A. for (i in 5 downTo 1) { println(i) }

B. for (i in 1..5 step -1) { println(i) }

C. for (i in 5..1) { println(i) }

D. for (i in 1 downTo 5) { println(i) }

Solution

1. Step 1: Identify correct descending range syntax

   Kotlin uses downTo to count down from a higher number to a lower number.

2. Step 2: Check each option

   for (i in 5 downTo 1) { println(i) } uses 5 downTo 1, which is correct. for (i in 5..1) { println(i) } uses an invalid range (5..1). for (i in 1..5 step -1) { println(i) } tries to use negative step incorrectly. for (i in 1 downTo 5) { println(i) } reverses the range incorrectly.

3. Final Answer:

   for (i in 5 downTo 1) { println(i) } -> Option A

4. Quick Check:

   Use downTo for descending loops [OK]

Hint: Use downTo to count down in Kotlin loops [OK]

Common Mistakes:

• Using .. for descending ranges
• Trying negative step with .. (not allowed)
• Swapping start and end in downTo

3. What is the output of this Kotlin code?

var sum = 0
for (i in 1..5 step 2) {
  sum += i
}
println(sum)

medium

A. 6

B. 15

C. 9

D. 10

Solution

1. Step 1: Understand the loop range and step

   The loop runs from 1 to 5, stepping by 2: values are 1, 3, 5.

2. Step 2: Calculate the sum of these values

   sum = 0 + 1 + 3 + 5 = 9

3. Final Answer:

   9 -> Option C

4. Quick Check:

   1 + 3 + 5 = 9 [OK]

Hint: Add numbers in steps to find sum quickly [OK]

Common Mistakes:

• Adding all numbers 1 to 5 instead of stepping
• Using step as a multiplier
• Confusing step with downTo

4. Find the error in this Kotlin code snippet:

for (i in 10..1 step 2) {
  println(i)
}

medium

A. println cannot be used inside for loop

B. step cannot be used with ranges

C. Variable i is not declared

D. Range 10..1 is invalid for counting down

Solution

1. Step 1: Analyze the range 10..1

   The range 10..1 tries to count up from 10 to 1, which is invalid because 10 is greater than 1.

2. Step 2: Understand correct descending syntax

   To count down, use downTo instead of .., e.g., 10 downTo 1 step 2.

3. Final Answer:

   Range 10..1 is invalid for counting down -> Option D

4. Quick Check:

   Use downTo for descending ranges [OK]

Hint: .. always counts up; use downTo to count down [OK]

Common Mistakes:

• Using .. for descending ranges
• Thinking step fixes descending range
• Ignoring Kotlin's range direction rules

5. You want to print all even numbers from 2 to 20 inclusive using a for loop in Kotlin. Which code snippet correctly does this?

hard

A. for (i in 2..20 step 2) { println(i) }

B. for (i in 2..19) { if (i % 2 == 0) println(i) }

C. for (i in 2 downTo 20 step 2) { println(i) }

D. for (i in 1..10 step 2) { println(i * 2) }

Solution

1. Step 1: Identify the range and step for even numbers

   Even numbers from 2 to 20 can be generated by starting at 2 and stepping by 2 up to 20.

2. Step 2: Check each option

   for (i in 2..20 step 2) { println(i) } uses 2..20 step 2, which prints 2,4,6,...,20 correctly. for (i in 2..19) { if (i % 2 == 0) println(i) } ends at 19 so prints evens up to 18, missing 20. for (i in 2 downTo 20 step 2) { println(i) } counts down incorrectly. for (i in 1..10 step 2) { println(i * 2) } prints 2,6,10,..., not all even numbers.

3. Final Answer:

   for (i in 2..20 step 2) { println(i) } -> Option A

4. Quick Check:

   Use step 2 from 2 to 20 for evens [OK]

Hint: Use step 2 starting at 2 to print even numbers [OK]

Common Mistakes:

• Using downTo instead of .. for ascending
• Forgetting to step by 2
• Multiplying inside loop incorrectly