Do-while loops in Kotlin are a powerful control flow structure that allows you to execute a block of code repeatedly while a specific condition is true. Unlike Kotlin While Loops, do-while loops guarantee at least one execution of the code block before checking the condition.

Syntax

The basic syntax of a do-while loop in Kotlin is as follows:

do {
    // Code block to be executed
} while (condition)

The code block within the do {...} section is executed first, and then the condition is evaluated. If the condition is true, the loop continues; otherwise, it terminates.

Usage and Examples

Do-while loops are particularly useful when you need to ensure that a block of code runs at least once, regardless of the initial condition. Here's a simple example:

var count = 0
do {
    println("Count: $count")
    count++
} while (count < 5)

In this example, the loop will print the count and increment it, continuing until the count reaches 5. Even if the initial count was greater than or equal to 5, the code block would still execute once.

Practical Application

Do-while loops are often used in scenarios where user input validation is required. For instance:

var userInput: Int
do {
    print("Enter a positive number: ")
    userInput = readLine()?.toIntOrNull() ?: -1
} while (userInput <= 0)

println("You entered: $userInput")

This loop ensures that the user enters a positive number. It will keep prompting the user until a valid input is provided.

Considerations and Best Practices

Always ensure there's a way to exit the loop to avoid infinite loops.
Use do-while when you need to execute the code block at least once before checking the condition.
Consider using break and continue statements for more complex loop control.
Be cautious with do-while loops in performance-critical code, as they always execute at least once.

Comparison with While Loops

While do-while loops are similar to while loops, they differ in their execution order:

Do-While Loop	While Loop
Executes the code block first, then checks the condition	Checks the condition first, then executes the code block
Guarantees at least one execution	May not execute at all if the initial condition is false

Choose the appropriate loop structure based on your specific requirements and the logic of your program.

Conclusion

Do-while loops in Kotlin offer a unique control flow that ensures at least one execution of a code block. They are particularly useful for input validation, menu-driven programs, and scenarios where you need to perform an action before checking a condition. By understanding and utilizing do-while loops effectively, you can create more robust and flexible Kotlin programs.