Conditionals

Conditionals in Dart are responsible for controlling the flow of a program. They are the basic building blocks for decision-making. Conditionals allow a block of code to be executed after specific predefined conditions are met based on whether they are true or false. Some of the common conditional statements that Dart includes are if-else, if-else-if ladder, switch and conditional expressions.

if Statement

The if statement gets executed when a block of code satisfies a specific condition, i.e., when the condition becomes true.

Syntax

if(condition){
  // Code to be executed
}

Example

The following example demonstrates the usage of the if statement:

void main(){
  int age = 18;
  if(age >= 18){
    print("You are an adult.You are eligible to vote");
  }
}

Here is the output:

You are an adult.You are eligible to vote

if-else Statement

The if-else statement is a combination of if and else statements. This statement executes the if block if a specific condition is true and executes the else block if it’s false.

Syntax

if(condition){
  // Code to be executed if and only if the condition is true
}else{
  // Code to be executed if the above condition is false
}

Example

The following example demonstrates the usage of the if-else statement:

void main(){
  int age = 12;

  if(age>=18){
    print("You are an adult.You are eligible to vote.");
  } else {
    print("Oops! You aren't eligible to vote.");
  }
}

Here is the output:

Oops! You aren't eligible to vote.

Nested if-else Statement

Dart supports nested if-else statements. These statements include multiple if-else conditions nested in one another. They are used to handle more complex conditions.

Syntax

if(condition1) {
  // Code to be executed if condition1 is true
  if(condition2) {
    // Code to be executed if condition1 and condition2 are both true
  } else {
    // Code to be executed if condition1 is true but condition2 is false
  }
} else {
  // Code to be executed if condition1 is false
  if(condition3){
    // Code to be executed if condition1 is false and condition3 is true
  } else {
    // Code to be executed if both condition1 and condition3 are false
  }
}

Example

The following example demonstrates the usage of nested if-else statements:

void main(){
  int age = 20;
  bool hasID = true;
  if (age>=18){
    if(hasID){
      print("You have Voter ID. Hence are eligible to vote");
    } else {
      print("You need an Voter ID.");
    }
  } else {
    print("You are not allowed to vote.");
  }
}

Here is the output:

You have Voter ID. Hence are eligible to vote

if-else-if Ladder

An if-else-if ladder is used to handle multiple statements sequentially. It executes the code block associated with the very first true condition it meets and else executes the else block.

Syntax

if (condition1) {
    // Code to execute if condition1 is true
  } else if (condition2) {
    // Code to execute if condition1 is false but condition2 is true
  } else if (condition3) {
    // Code to execute if condition1 and condition2 are false but condition3 is true
  } else {
    // Code to execute if all the above conditions are false
}

Example

The following example demonstrates the usage of the if-else-if ladder:

void main(){
int age = 25;
if(age >= 0 && age <= 12){
  print ("Category: Child");
  } else if (age >= 13 && age <=19){
    print("Category: Teenager");
  } else if (age >= 20 && age <=64){
    print("Category: Adult");
  } else if (age >= 65){
    print("Category: Senior");
  } else {
    print("Please enter a valid age");
  }
}

Here is the output:

Category: Adult

switch Statement

The switch statement is used to execute a code block based on a specific value of a expression. It is composed of several cases which specify a unique value to be compared to the value of the expression. The break statement terminates the switch statement. The default case contains a code block to be executed if none of the cases match the value of the expression specified in switch.

Syntax

switch (expression) {
  case value1:
    // Code to execute if expression == value1
    break;
  case value2:
    // Code to execute if expression == value2
    break;
  case value3:
    // Code to execute if expression == value3
    break;
  default:
    // Code to execute if the value of the expression does not match any case
}

Example

The following example demonstrates the usage of the switch statement:

void main(){
int age = 25;
  String category;
  if (age >= 0 && age <= 12) {
    category = 'Child';
  } else if (age >= 13 && age <= 19) {
    category = 'Teenager';
  } else if (age >= 20 && age <= 64) {
    category = 'Adult';
  } else if (age >= 65) {
    category = 'Senior';
  } else {
    category = 'Invalid age';
  }
  switch (category) {
    case 'Child':
      print('Category: Child');
      break;
    case 'Teenager':
      print('Category: Teenager');
      break;
    case 'Adult':
      print('Category: Adult');
      break;
    case 'Senior':
      print('Category: Senior');
      break;
    default:
      print('Invalid age');
  }
}

Here is the output:

Category: Adult

Conditional Expressions

Conditional expressions in Dart are created using the ?? operator, which is known as null-aware operator. It gets evaluated only if the expression is null and returns the value on its right-hand side.

Syntax

condition ? expressionIfTrue : expressionIfFalse;

Example

The following example demonstrates the usage of conditional expressions:

void main(){
  String? userName;

  String displayName = userName ?? 'Guest';
    print("Welcome, $displayName!");
}

Here is the output:

Welcome, Guest!