Kotlin Program Flow Control

Controlling Program Flow

• Program statements are executed sequentially by default, one after the other, in a linear fashion.
• There are constructs that can cause programs to deviate from this linear flow.
• Some constructs cause the flow to fork or branch.
• Other constructs cause the program flow to loop.

The when Statement

• Kotlin does not have a switch statement, but it uses a when construct.
• Its form and structure are similar to switch.
• A simple example implements a when statement to find the day of the week using a Calendar instance.
• The when matches the argument against all branches sequentially.
• When a match is found, it doesn't continue to the next branch.
• No break statement needed.
• The when construct can also be used as an expression. Each branch's value becomes the return value of the expression. The else clause is required in this case.

How to Write Branches Inside the when Construct

• An example demonstrates how to use a when statement with a variable to determine the answer to life.
• The variable is initialized using input from the user.
• The different branches are based on the value of the variable.
• The example shows conditional branches, ranges and matching patterns.

The while Statement

• while and do...while statements in Kotlin work similarly to those in Java.
• These are statements, not expressions.
• Code example provides a refresher on while loop usage.
• A flowchart outlines the structure of a while loop.

Example of Compute sum of Natural Numbers

• Python program example for computing the sum of natural numbers up to 100.

do...while Loop

• The do...while loop executes the code block once before evaluating the loop condition.
• The syntax in Kotlin follows the pattern of do { } while (condition).

Flowchart of do...while Loop

• A flowchart visually depicts the workings of the do...while loop. The loop body runs first, then the expression is evaluated.

The Program below calculates the sum of numbers...

• A program example to compute the sum of numbers entered by users until a 0 entry is made.
• The code uses a do...while loop for this functionality. The user inputs numbers until they input 0.

for loops

• Example uses a for loop to iterate through a string array of words created by splitting a string.

Ranges

• If needing to work with numbers in for loops, Ranges are used in Kotlin.
• Ranges are a type that represents an arithmetic progression of integers, created with rangeTo().
• Example for loop with range from 1-10.

Exception Handling

• Kotlin's exception handling is similar to Java's using try, catch, and potentially a finally block.
• Kotlin simplifies this by using unchecked exceptions, making try...catch blocks optional.
• The optional example shows reading a file and handling potential errors.

Kotlin program of using try-catch as an expression

• This Kotlin program demonstrates performing an arithmetic operation and handling potential ArithmeticException exceptions using a try, catch block—useful for handling arithmetic errors.
• This example shows using try/catch to handle exceptions during arithmetic and how this works in a simple program that takes user input and performs an arithmetic division.

Handling Nulls

• When declaring a variable of type String, it cannot be directly set to null in Kotlin.
• Null values can be handled using optional types and the safe-call operator.
• Example demonstrates how to handle potential null values in a Kotlin program.

Safe Call Operator

• Kotlin introduced a safe-call operator (?).
• This operator can handle nullable types, performing the null check and avoiding potential errors caused by null values.

Examples

• Kotlin example of checking for empty, blank, and null strings.