Using Case Statements To Simplify Conditional Logic

Reducing Complexity with Case Statements

Conditional logic is ubiquitous in programming. We often need to execute different code blocks based on the state of variables or the flow of program execution. However, nested if-else statements and chained conditional logic can quickly become complex and hard to reason about.

Case statements provide a way to simplify complex conditional logic by allowing us to associate blocks of code with specified conditions. Rather than having to nest conditionals or chain sequential tests, we can use a case statement to cleanly map conditions to actions.

In this article, we’ll cover common problems with conditional nesting, explain how case statements work, look at examples, and offer tips for using case statements effectively.

The Problem of Nested Conditionals

Nested if-else conditionals are a common source of complexity. Each new level of nesting adds more possible branches that have to be reasoned about. Take this nested set of conditionals:

if (x > 10) {
  if (y > 5) {
    // do A
  } else {
    // do B
  }
} else {
  if (z == 0) {
    // do C
  } else {
    // do D
  }
}

Following the precise flow requires visualizing each if-else branch. As more conditions are added, the number of paths grows exponentially. The complexity impacts readability, testing, and maintenance.

Chained conditionals can also obscure logic flow:

if (a) {
  // ...
} else if (b) {
  // ... 
} else if (c) {
  // ...
} else {
  // ...
}

It may not be clear which condition leads to what code without tracing each path. Logic changes can require substantial rewrite of conditional chains.

How Case Statements Work

Case statements avoid the deeply nested logic of chained if-else conditionals. Rather than placing conditional logic inside other conditionals, case statements allow us to map discrete conditional tests to blocks of code.

Syntax and Structure

The basic syntax of a case statement is:

switch(expression) {
  case condition1:
    // code block 1
    break;
  
  case condition2:
    // code block 2
    break;

  default:
    // default code block
}

The switch expression is evaluated once. The value is then compared to the various case conditions using strict equality (===) checks. When a match is found, execution jumps to that case’s code block. The break statements then exit the block.

Matching Conditions

Case conditions can take several forms:

• Literal values like numbers, strings, or booleans
• Expressions like variables or function calls
• Value ranges with inclusive start and exclusive end bounds

Multiple case labels can refer to the same block, allowing a logical OR conditional:

case 1: 
case 2:
case 3:
  // Executes if expression is 1, 2, or 3

The case values must be compile-time constants. They cannot be variables or expressions that require runtime evaluation.

Executing Code Blocks

When a matching condition evaluates to true, execution jumps to that case’s associated block of code. The break statement then exits the block.

Without break statements, execution will continue sequentially through subsequent case blocks. This fallthrough behavior may be desirable in some instances.

The default case block executes if no case condition matched. It is equivalent to an else block in an if statement. Default cases are optional.

Case Statement Examples

To demonstrate the use of switch case statements, let’s look at some common examples.

Reading User Input

We can use a switch statement to take different actions based on user input:

const command = readline();

switch (command) {
  case 'lookup': 
    lookupRecord();
    break;
  case 'add':
    addRecord();
    break;
  case 'edit':
    updateRecord();
    break;
  case 'delete':
    deleteRecord();
    break;
  default:
    invalidCommand();
}

This allows us to cleanly associate a block of code with each possible command, rather than nesting conditionals.

Handling Errors

We can also use case statements to handle different error conditions:

const error = getError();

switch (error) {
  case 'connectionFailure':
    showConnectionAlert();
    retryRequest();    
    break;
  
  case 'authenticationError': 
    showLoginPrompt();
    break;

  case 'timeout':
    showTimeoutWarning();
    retryRequest();
    break;

  default:
    showGenericError();
}

This extracts error handling into an independent conditional structure instead of intermixing with other code.

Menu Systems

Case statements shine when implementing menu systems:

let selection;

while (true) {

  showMainMenu();

  selection = getInput();

  switch(selection) {
    case '1':
      showTutorial();
      break;

    case '2':
      showCalendar();
      break;
    
    case '3':
      showSettings();
      break;
    
    case '4':
     exitApp();
     break;

    default:
      invalidChoice();
  }

}

The menu logic stays neatly encapsulated instead of requiring nested conditionals dependent on wider program state.

Tips for Effective Use

Here are some key tips for using case statements effectively:

Fallthrough Behavior

Recall that without break statements, execution falls through subsequent blocks. Be aware of unintended consequences from fallthrough:

switch(n) {
  case 1: 
    // Runs if n == 1 AND n == 2  
    init(); 

  case 2:
    loadData();
}

Break statements usually increase clarity by separating control paths.

Default Clause

The default clause handles unmatched conditions. It’s good practice to include a default case either for error handling or to explicitly do nothing:

default:
  // Explicitly ignoring no-match

This guards against unexpected control flow from new conditions.

Readability

Break case conditions into separate lines for readability:

case 
  veryLongCondition1() ||
  otherVeryLongCondition2():

  // code block

Consistency in layout also aids understanding at a glance.