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Kotlin Control Flow and Array Operations Explained

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Kotlin when

As with the preparation of manyif..else expression, you can usewhen expression, it is more readable.

It is used to select one of multiple code blocks to be executed:

typical example

Use the number of the day of the week to calculate the name of the day of the week:

val day = 4

val result = when (day) {
  1 -> "Monday"
  2 -> "Tuesday"
  3 -> "Wednesday"
  4 -> "Thursday"
  5 -> "Friday"
  6 -> "Saturday"
  7 -> "Sunday"
  else -> "Invalid day."
}
println(result)

// output "Thursday" (day is 4)

when expression is similar to the Javaswitch Statements.

It works as follows:

  1. treat (sb a certain way)when Variables (day) Conduct an assessment.
  2. commander-in-chief (military)day The value of the variable is compared to the value of each "branch".
  3. Each branch starts with a value followed by an arrow (->) and a result.
  4. If it matches, the associated code block is executed.
  5. utilizationelse Specifies the code to run if there is no match.

In the example above, theday The value of the4The printout will therefore be"Thursday"。

Kotlin While loop

Loops can execute a block of code when a specified condition is reached. Loops are very handy because they save time, reduce errors, and make code more readable.

Kotlin while circulate

while The loop pass condition istrue When you loop through a block of code:

grammatical

while (condition) {
  // The block to execute
}

In the following example, as long as the counter variablei less than5The code in the loop will run over and over again:

typical example

var i = 0
while (i < 5) {
  println(i)
  i++
}

Note: Don't forget to add the variables used in the condition or the loop will never end.

Kotlin do..while circulate

do..while The loop iswhile A variant of the loop. This loop will check if the condition istrue Execute the block once before, and then as long as the condition istrueand it repeats the execution loop.

grammatical

do {
  // The block to execute
} while (condition)

The following example uses thedo/while Loop. Even if the condition isfalse, the loop will also be executed at least once, because the code block will be executed before the test condition:

typical example

var i = 0
do {
  println(i)
  i++
} while (i < 5)

The above is a brief description of thewhen expressions as well aswhile cap (a poem)do..while Loops are described in detail. These features make writing and understanding conditions and loops easier and more intuitive.

Kotlin Break and Continue

Kotlin Break

breakstatement is used to jump out of the loop.

In the following example, when thei be tantamount to4 when it jumps out of the loop:

var i = 0
while (i < 10) {
  println(i)
  i++
  if (i == 4) {
    break
  }
}

Kotlin Continue

continuestatement is used to skip the code for a specific condition in one iteration of the loop and continue to the next iteration.

In the following example, the skip values are4 The situation:

var i = 0
while (i < 10) {
  if (i == 4) {
    i++
    continue
  }
  println(i)
  i++
}

Kotlin Arrays

Kotlin arrays

Arrays are used to store multiple values in a single variable rather than creating separate variables for each value.

To create an array, use thearrayOf() function and place a comma-separated list of values in it:

val cars = arrayOf("Volvo", "BMW", "Ford", "Mazda")

Accessing array elements

You can access an array element by referencing the index number (inside square brackets).

In this example, we access thecars The value of the first element in the array:

val cars = arrayOf("Volvo", "BMW", "Ford", "Mazda")
println(cars[0])
// Output Volvo

Note: The array index starts at0 Start:[0] is the first element.[1] is the second element, and so on.

Modifying array elements

To change the value of a specific element, quote the index number:

cars[0] = "Opel"

Example:

val cars = arrayOf("Volvo", "BMW", "Ford", "Mazda")
cars[0] = "Opel"
println(cars[0])
// Now output Opel instead of Volvo

Array length/size

To find out how many elements are in an array, use thesize Properties:

val cars = arrayOf("Volvo", "BMW", "Ford", "Mazda")
println()
// Output 4

Checking for the existence of an element

You can use thein operator to check for the presence of elements in the array:

val cars = arrayOf("Volvo", "BMW", "Ford", "Mazda")
if ("Volvo" in cars) {
  println("Exists!")
} else {
  println("Does not exist.")
}

Iterate over the array

Usually when working with arrays, you need to iterate through all the elements.

You can use thefor Loop over array elements, about which you will learn more in the next chapter.

The following sample outputcars All elements in the array:

val cars = arrayOf("Volvo", "BMW", "Ford", "Mazda")
for (x in cars) {
  println(x)
}

The above is a brief description of thebreak、continue as well as a detailed description of basic array operations. These features make controlling loop flow and managing multiple data items more flexible and efficient.

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