Practice Problems: Kotlin Basics

Posted on 20th Oct 2023 00:00:00 in pinned

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2. Print messages
Tell your friends what you learned in this pathway.

Can you write a main() function that prints these messages on four separate lines?

Use the val keyword when the value doesn't change.
Use the var keyword when the value can change.
When you define a function, you define the parameters that can be passed to it.
When you call a function, you pass arguments for the parameters.

ans

fun main(){
println("Use the val keyword when the value doesn't change. ")
println("Use the var keyword when the value can change.")
println("When you define a function, you define the parameters that can be passed to it. ")
println("When you call a function, you pass arguments for the parameters.")
}

3. Fix compile error
This program prints a message that notifies the user that they received a chat message from a friend.


fun main() {
println("New chat message from a friend'}
}
Can you figure out the root cause of the compile errors in this program and fix them?
Does the code use appropriate symbols to indicate the open and close of the string and function argument?
Hint: You can use Kotlin Playground to run the code and view the compilation errors.

After you fix the errors, the program should compile without errors and print this output:


New chat message from a friend

ans

fun main() {
println("New chat message from a friend")
}

4. String templates
This program informs users about the upcoming promotional sale on a particular item. It has a string template, which relies on the discountPercentage variable for the percent discount and the item variable for the item on sale. However, there are compilation errors in the code.


fun main() {
val discountPercentage: Int = 0
val offer: String = ""
val item = "Google Chromecast"
discountPercentage = 20
offer = "Sale - Up to $discountPercentage% discount on $item! Hurry up!"

println(offer)
}
Can you figure out the root cause of the errors and fix them?
Can you determine the output of this program before you run the code in Kotlin Playground?
Hint: Can you re-assign a value to a read-only variable?

After you fix the errors, the program should compile without errors and print this output:


Sale - Up to 20% discount on Google Chromecast! Hurry up!

ans

fun main() {
var discountPercentage: Int = 0
var offer: String = ""
val item = "Google Chromecast"
discountPercentage = 20
offer = "Sale - Up to $discountPercentage% discount on $item! Hurry up!"

println(offer)
}

5. String concatenation
This program displays the total party size. There are adults and kids at the party. The numberOfAdults variable holds the number of adults at the party and the numberOfKids variable holds the number of kids.


fun main() {
val numberOfAdults = "20"
val numberOfKids = "30"
val total = numberOfAdults + numberOfKids
println("The total party size is: $total")
}
Step 1
Can you determine the output of this program before you run the code in Kotlin Playground?
After you determine the output, run the code in Kotlin Playground and then check if your output matches the output displayed.

Hint: What happens when you use the + operator on two strings?

Step 2
The code works and prints some output, but the output doesn't show the total number of people attending the party.

Can you find the issue in the code and fix it so that it prints this output?

The total party size is: 50

ans

fun main() {
val numberOfAdults = 20
val numberOfKids = 30
val total = numberOfAdults + numberOfKids
println("The total party size is: $total")
}

6. Message formatting
This program displays the total salary that an employee receives this month. The total salary is divided in two parts: the baseSalary variable, which the employee receives every month, and the bonusAmount variable, which is an additional bonus awarded to the employee.


fun main() {
val baseSalary = 5000
val bonusAmount = 1000
val totalSalary = "$baseSalary + $bonusAmount"
println("Congratulations for your bonus! You will receive a total of $totalSalary (additional bonus).")
}
Can you figure out the output of this code before you run it in Kotlin Playground?
When you run the code in Kotlin Playground, does it print the output that you expected?

ans

fun main() {
val baseSalary = 5000
val bonusAmount = 1000
val totalSalary = baseSalary + bonusAmount
println("Congratulations for your bonus! You will receive a total of $totalSalary (additional bonus).")
}

7. Implement basic math operations
In this exercise, you write a program that performs basic math operations and prints the output.

Step 1
This main() function contains one compile error:


fun main() {
val firstNumber = 10
val secondNumber = 5

println("$firstNumber + $secondNumber = $result")
}
Can you fix the error so that the program prints this output?

10 + 5 = 15

ans
step 1
fun main() {
val firstNumber = 10
val secondNumber = 5
var result = firstNumber + secondNumber
println("$firstNumber + $secondNumber = $result")
}

shows 10 + 5 = 15



Step 2
The code works, but the logic for adding two numbers is located within the result variable, making your code less flexible to reuse. Instead, you can extract the addition operation into an add() function so that the code is reusable. To do this, update your code with the code listed below. Notice that the code now introduces a new val called thirdNumber and prints the result of this new variable with firstNumber.


fun main() {
val firstNumber = 10
val secondNumber = 5
val thirdNumber = 8

val result = add(firstNumber, secondNumber)
val anotherResult = add(firstNumber, thirdNumber)

println("$firstNumber + $secondNumber = $result")
println("$firstNumber + $thirdNumber = $anotherResult")
}

// Define add() function below this line
Can you define the add() function so that the program prints this output?

10 + 5 = 15
10 + 8 = 18

ans step 2

fun main() {
val firstNumber = 10
val secondNumber = 5
val thirdNumber = 8

val result = add(firstNumber, secondNumber)
val anotherResult = add(firstNumber, thirdNumber)

println("$firstNumber + $secondNumber = $result")
println("$firstNumber + $thirdNumber = $anotherResult")
}

fun add(a: Int, b: Int): String {
val result = a + b
return "$result"
}

shows
10 + 5 = 15
10 + 8 = 18


Step 3
Now you have a reusable function to add two numbers.

Can you implement the subtract() function the same way you implemented the add() function? Modify the main() function as well to use the subtract() function so you can verify that it works as expected.
Hint: Think about the difference between addition, subtraction and other math operations. Start work on the solution code from there.

ans

fun main() {
val firstNumber = 10
val secondNumber = 5
val thirdNumber = 8

val result = subtract(firstNumber, secondNumber)
val anotherResult = subtract(firstNumber, thirdNumber)

println("$firstNumber - $secondNumber = $result")
println("$firstNumber - $thirdNumber = $anotherResult")
}

fun subtract(a: Int, b: Int): String {
val result = a - b
return "$result"
}

shows
10 - 5 = 5
10 - 8 = 2


8. Default parameters
Gmail has a feature that sends a notification to the user whenever a login attempt is made on a new device.

In this exercise, you write a program that displays a message to users with this message template:


There's a new sign-in request on operatingSystem for your Google Account emailId.
You need to implement a function that accepts an operatingSystem parameter and an emailId parameter, constructs a message in the given format, and returns the message.

For example, if the function was called with "Chrome OS" for the operatingSystem and "sample@gmail.com" for the emailId, it should return this string:


There's a new sign-in request on Chrome OS for your Google Account sample@gmail.com.
Step 1
Can you implement the displayAlertMessage() function in this program so that it prints the output displayed?

fun main() {
val operatingSystem = "Chrome OS"
val emailId = "sample@gmail.com"

println(displayAlertMessage(operatingSystem, emailId))
}

// Define your displayAlertMessage() below this line.
Does your program print this output?

There's a new sign-in request on Chrome OS for your Google Account sample@gmail.com.

ans

fun main() {
val operatingSystem = "Chrome OS"
val emailId = "sample@gmail.com"

println(displayAlertMessage(operatingSystem, emailId))
}

// Define your displayAlertMessage() below this line.
fun displayAlertMessage(operatingSystem: String, emailId: String):String {
val operatingSystem = "$operatingSystem"
val emailId = "$emailId"
return "There's a new sign-in request on $operatingSystem for your Google Account $emailId"
}


Step 2
Great job! You displayed the message. However, in some cases, you discover that you can't determine the user's operating system. In such cases, you need to specify the operating system name as Unknown OS. You can further optimize the code so that you don't need to pass the Unknown OS argument each time that the function is called.

Can you find a way to optimize the code with this information so that it prints this output?

There's a new sign-in request on Unknown OS for your Google Account user_one@gmail.com.

There's a new sign-in request on Windows for your Google Account user_two@gmail.com.

There's a new sign-in request on Mac OS for your Google Account user_three@gmail.com.
To print the above message, replace the main() function implementation with this one:

fun main() {
val firstUserEmailId = "user_one@gmail.com"

// The following line of code assumes that you named your parameter as emailId.
// If you named it differently, feel free to update the name.
println(displayAlertMessage(emailId = firstUserEmailId))
println()

val secondUserOperatingSystem = "Windows"
val secondUserEmailId = "user_two@gmail.com"

println(displayAlertMessage(secondUserOperatingSystem, secondUserEmailId))
println()

val thirdUserOperatingSystem = "Mac OS"
val thirdUserEmailId = "user_three@gmail.com"

println(displayAlertMessage(thirdUserOperatingSystem, thirdUserEmailId))
println()
}

ans

fun main() {
val firstUserEmailId = "user_one@gmail.com"

// The following line of code assumes that you named your parameter as emailId.
// If you named it differently, feel free to update the name.
println(displayAlertMessage(emailId = firstUserEmailId))
println()

val secondUserOperatingSystem = "Windows"
val secondUserEmailId = "user_two@gmail.com"

println(displayAlertMessage(secondUserOperatingSystem, secondUserEmailId))
println()

val thirdUserOperatingSystem = "Mac OS"
val thirdUserEmailId = "user_three@gmail.com"

println(displayAlertMessage(thirdUserOperatingSystem, thirdUserEmailId))
println()
}

// Define your displayAlertMessage() below this line.
fun displayAlertMessage(operatingSystem: String = "Unknown OS", emailId: String):String {
val operatingSystem = "$operatingSystem"
val emailId = "$emailId"
return "There's a new sign-in request on $operatingSystem for your Google Account $emailId"
}

shows

There's a new sign-in request on Unknown OS for your Google Account user_one@gmail.com

There's a new sign-in request on Windows for your Google Account user_two@gmail.com

There's a new sign-in request on Mac OS for your Google Account user_three@gmail.com


9. Pedometer
The pedometer is an electronic device that counts the number of steps taken. Nowadays, almost all mobile phones, smart watches, and fitness gear come with pedometers built into them. The health and fitness app uses built-in pedometers to calculate the number of steps taken. This function calculates the number of calories that the user burns based on the user's number of steps.

Can you rename the functions, function parameters, and variables in this program based on best practices?

fun main() {
val Steps = 4000
val caloriesBurned = PEDOMETERstepsTOcalories(Steps);
println("Walking $Steps steps burns $caloriesBurned calories")
}

fun PEDOMETERstepsTOcalories(NumberOFStepS: Int): Double {
val CaloriesBURNEDforEachStep = 0.04
val TotalCALORIESburned = NumberOFStepS * CaloriesBURNEDforEachStep
return TotalCALORIESburned
}

ans

fun main() {
val steps = 4000
val caloriesBurned = pedometerStepsToCalories(steps);
println("Walking $steps steps burns $caloriesBurned calories")
}

fun pedometerStepsToCalories(numberOfSteps: Int): Double {
val caloriesBurnedForEachStep = 0.04
val totalCaloriesBurned = numberOfSteps * caloriesBurnedForEachStep
return totalCaloriesBurned
}

10. Compare two numbers
Modern mobile phones have a built-in feature that tracks screen time, or the time you spend on your phone each day.

In this exercise, you implement a function that compares the time in minutes that you spent on your phone today versus the time spent yesterday. The function accepts two integer parameters and returns a boolean value.

The first parameter holds the number of minutes that you spent today and the second parameter holds the number of minutes that you spent yesterday. The function returns a true value if you spent more time on the phone today compared to yesterday. Otherwise, it returns a false value.

For example, if you called the function with these named arguments:

timeSpentToday = 300 and timeSpentYesterday = 250, the function returns a true value.
timeSpentToday = 300 and timeSpentYesterday = 300, the function returns a false value.
timeSpentToday = 200 and timeSpentYesterday = 220, the function returns a false value.
Hint: The > comparison operator returns a true value if the value before the operator is greater than the value after it. Otherwise, it returns a false value.

ans

fun main() {
val timeSpentToday = 550
val timeSpentYesterday = 300
val result = screenTime(timeSpentToday, timeSpentYesterday);
println("$result")
}

fun screenTime(timeSpentToday: Int, timeSpentYesterday: Int): Boolean {
if (timeSpentToday > timeSpentYesterday) {
return true
}else{
return false
}

}

11. Move duplicate code into a function
This program displays the weather for different cities. It includes the city name, the high and low temperature for the day, and the chance of rain.


fun main() {
println("City: Ankara")
println("Low temperature: 27, High temperature: 31")
println("Chance of rain: 82%")
println()

println("City: Tokyo")
println("Low temperature: 32, High temperature: 36")
println("Chance of rain: 10%")
println()

println("City: Cape Town")
println("Low temperature: 59, High temperature: 64")
println("Chance of rain: 2%")
println()

println("City: Guatemala City")
println("Low temperature: 50, High temperature: 55")
println("Chance of rain: 7%")
println()
}
There are many similarities in the code that prints the weather for each city. For example, there are phrases that are repeated multiple times, such as "City:" and "Low temperature:". Similar, repeated code creates the risk of errors in your program. For one of the cities, you may have a typo or you may forget one of the weather details.

Can you create a function that prints the weather details for a single city to reduce the repetition in the main() function and then do the same for the remaining cities?
Can you update the main() function to call the function that you created for each city and pass in the appropriate weather details as arguments?

ans

fun main() {
println(weather("Ankara",27, 31, 82))
println(weather("Tokyo",32, 36, 18))
println(weather("Cape Town",59, 64, 2))
println(weather("Guatemala City",50, 55, 7))
}

fun weather(city:String, l:Int, h:Int, rain:Int):String {
val city = city
val h = h
val l = l
val rain = rain
return "City $city\nLow temperature: $l, High temperature: $h\nChance of rain: $rain %\n"
}

shows

City Ankara
Low temperature: 27, High temperature: 31
Chance of rain: 82 %

City Tokyo
Low temperature: 32, High temperature: 36
Chance of rain: 18 %

City Cape Town
Low temperature: 59, High temperature: 64
Chance of rain: 2 %

City Guatemala City
Low temperature: 50, High temperature: 55
Chance of rain: 7 %