Flow Control in Dart

Introduction

Mastering flow control is key to writing efficient and organized code. In Dart, flow control empowers developers to dictate how their programs execute, making it possible to navigate through various scenarios and handle unexpected situations gracefully. From conditional statements that branch program flow based on conditions to loops that handle repetitive tasks, Dart provides a rich set of tools. Additionally, error handling with exception management and assertion statements for debugging further enhance the language's versatility. Whether you're a beginner or an experienced developer, understanding Dart's flow control mechanisms is essential for building robust and reliable applications.

Conditional Statements

Conditional statements in Dart are used to control the flow of a program based on certain conditions. They allow you to execute different blocks of code depending on whether a given condition is true or false. Dart supports three main types of conditional statements: if statements, else-if statements, and switch statements.

1. if statement In Dart, the if statement is a fundamental control flow construct that allows you to conditionally execute code based on a certain condition. It allows your program to make decisions and perform different actions based on whether a condition is true or false.

• Syntax and usage: The basic syntax of an if statement in Dart is as follows:

Here, condition is an expression that evaluates to a boolean value (true or false). If the condition is true, the code block inside the curly braces {} will be executed; otherwise, it will be skipped, and the program will move on to the next line of code.

Example:

Output:

In this example, the if statement checks whether the age is greater than or equal to 18. Since the condition is true (age is 25), the code inside the if block is executed, and "You are an adult." is printed.

• Handling multiple conditions using else if: You can extend the if statement to handle multiple conditions using the else if clause. The else if allows you to check additional conditions when the initial if condition is false.

The syntax is as follows:

• Example:

• Output:

In this example, the else if statement checks an additional condition. If the first if condition (age >= 18) is false, it moves on to the else if condition (age >= 13). Since the age is 12, the second condition is true, and "You are a teenager." is printed.

• Nesting if statements: You can also nest if statements inside other if or else blocks to create more complex decision-making structures. This allows you to evaluate multiple conditions and execute different code blocks accordingly.

Example:

Output:

In this example, the nested if statement checks whether the person is employed or not, but only if the age is 18 or greater. Since the age is 25 and isEmployed is true, both nested conditions are true, and both corresponding messages are printed.

Remember to use proper indentation and maintain the code's readability when nesting multiple if statements to avoid confusion and potential errors.

1. switch statement In Dart, the switch statement is another control flow construct that allows you to simplify decision-making when you have multiple cases to consider. It is particularly useful when you want to compare the value of an expression against different constant values and execute different code blocks based on the matching case.

• Syntax and usage: The basic syntax of a switch statement in Dart is as follows:

In a switch statement, you specify the expression whose value you want to compare with different cases. The code inside the corresponding case block will be executed when the value of the expression matches the specified value.

The break statement is used to exit the switch block after a case is matched and executed. Without the break statement, Dart would continue executing the code for all the following cases, which is known as "fall-through behavior."

The default case is optional and is used to provide a code block that executes when none of the case values match the expression.

Example:

Output:

In this example, the switch statement checks the value of the fruit variable. Since the fruit is 'apple', the first case block is matched, and the message "Selected fruit is apple." is printed.

• Comparing switch with if-else: The switch statement is often compared with if-else statements because both can be used for conditional execution. However, they have some key differences and are suitable for different scenarios.

• Use switch when:

• You have a single expression (e.g., a variable) whose value needs to be compared against multiple constant values.

• The comparison values are simple and can be expressed as constants. * You want concise and readable code for handling multiple cases.

• Use if-else when:

• You have complex and non-constant conditions to evaluate.

• You need to check multiple conditions in a more flexible manner, and there are no fixed constant values to compare.

• You need to handle a range of values or complex boolean expressions.

Loops

In Dart, loops are control structures that allow you to repeatedly execute a block of code based on a certain condition. They are essential for automating repetitive tasks and iterating over collections of data. Dart supports two main types of loops: "for" loops and "while" loops.

for Loop

• Syntax and basic usage: The syntax of the for loop in Dart is as follows:

• Initialization: This part is executed before the loop starts and is usually used to initialize the loop control variable.
• Condition: It is a Boolean expression that is evaluated before each iteration. If the condition is true, the loop's body will be executed; otherwise, the loop terminates.
• update: This part is executed after each iteration and is typically used to modify the loop control variable. Here's a simple example of a for loop in Dart:

Output:

• Iterating over lists and collections: The for loop is often used to iterate over lists, arrays, or collections in Dart. To iterate over a collection, you can use the for loop in conjunction with the in keyword.

Here's an example of iterating over a list using the for loop:

Output:

You can also use the for loop to iterate over other collections like sets and maps.

• Using break and continue statements: Dart provides the break and continue statements to control the flow of a loop.

• break: It allows you to exit the loop prematurely when a certain condition is met. It terminates the loop and continues executing the code after the loop. Here's an example of using the break statement:

Output:

• continue: It allows you to skip the current iteration and move on to the next iteration of the loop. Here's an example of using the continue statement:

Output:

In this example, when i is equal to 3, the continue statement is executed, skipping the code below it for that particular iteration, and the loop proceeds to the next iteration.

while Loop

1. Syntax and basic usage: The while loop in Dart is another control structure used for the repetitive execution of a block of code. It repeatedly executes the code as long as a specified condition is true. The syntax of the while loop is as follows:

The condition is a Boolean expression that is evaluated before each iteration. If the condition is true, the code inside the while loop will be executed; otherwise, the loop terminates.

Here's a simple example of a while loop in Dart:

Output:

Differences between for and while loops

Advanced Flow Control in Dart

Ternary Operator:

The ternary operator in Dart is a concise way of writing conditional expressions. It allows you to evaluate a condition and return one of two expressions based on whether the condition is true or false. The syntax of the ternary operator is as follows:

Here, condition is the boolean expression that is evaluated, expression1 is returned if the condition is true, and expression2 is returned if the condition is false.

Let's look at a simple example to understand how the ternary operator works:

Output

In this example, if the 'number' is greater than 5, the ternary operator will return the string 'Greater than 5', and if the 'number' is less than or equal to 5, it will return the string 'Less than or equal to 5'.

The ternary operator is very useful for writing concise code when you have simple conditional expressions. However, it's essential to use it judiciously, as overly complex ternary expressions can make the code hard to read and understand.

Using assert for debugging:

The 'assert' statement in Dart is a powerful tool for ensuring code correctness during development. It allows you to specify conditions that should always be true at certain points in your code. If the condition evaluates to false, the 'assert' statement throws an exception, indicating a bug in the code.

The syntax of the 'assert' statement is as follows:

Here, 'condition' is the boolean expression that is expected to be true. If it's false, the assert statement will throw an AssertionError with an optional 'optionalMessage' string.

Let's see an example of using 'assert' to check a condition during development:

Output

In this example, we have a 'divide' function that takes two arguments, 'dividend' and 'divisor.' Before performing the division, we use an assert statement to ensure that the 'divisor' is not zero. If the 'divisor' is zero, the assert statement will throw an exception with the specified message.

During development, you can use 'assert' to catch potential bugs early and ensure that your code behaves as expected. However, note that 'assert' statements are automatically removed in production/release builds, so they won't affect the performance of your app.

Best Practices on Flow Control

• Choosing the right flow control structure: Selecting appropriate flow control structures, such as loops and conditionals, to efficiently manage the flow of a program, enhancing its performance and readability.
• Avoiding common pitfalls: Being aware of and avoiding typical mistakes or errors that programmers often encounter, leads to more reliable and bug-free code.
• Writing clean and readable code: Employing coding conventions and practices that make code easy to understand, maintain, and collaborate on, promoting better software quality and team productivity.