If-else logic is a foundational concept in programming that allows you to execute different sections of code based on the evaluation of specific conditions. In Dart, the if and else statements enable you to introduce decision-making capabilities into your applications, making them responsive to various inputs and situations.

Structure of If-Else Logic
 

Basic If-Else Statement

The basic structure of an if-else statement consists of the if condition followed by an optional else block.

Syntax:

if (condition) {
  // Code to execute if condition is true } else {
  // Code to execute if condition is false }

Example Use Cases

Example 1: Age Verification

Let's create a simple program that checks if a user is eligible to vote based on their age.

Code:

void main() {
  int age = 20; // Example age 
  if (age >= 18) {
    print('You are eligible to vote.');
  } else {
    print('You are not eligible to vote.');
  }
}

Code Explanation:

• int age = 20;: This line declares a variable age and assigns it the value 20.
• if (age >= 18) {: The program checks if age is greater than or equal to 18.
• If the condition is true, the program executes print('You are eligible to vote.');.
• If the condition is false, the else block executes, printing You are not eligible to vote..

Example 2: Grading System

Now, let's implement a grading system that assigns a letter grade based on a numeric score.

Code:

void main() {
  int score = 85; // Example score 
  if (score >= 90) {
    print('Grade: A');
  } else if (score >= 80) {
    print('Grade: B');
  } else if (score >= 70) {
    print('Grade: C');
  } else {
    print('Grade: D');
  }
}

Code Explanation:

• int score = 85;: This line declares a variable score and assigns it the value 85.
• The program uses multiple else if statements to check the score:
  • if (score >= 90) {: Checks if the score is 90 or higher; if true, it prints "Grade: A".
  • else if (score >= 80) {: Checks if the score is 80 or higher; if true, it prints "Grade: B".
  • else if (score >= 70) {: Checks if the score is 70 or higher; if true, it prints "Grade: C".
  • If none of the conditions are met, the else block executes, printing "Grade: D".

Example 3: Temperature Check

In this example, we will evaluate a temperature value and provide feedback based on its range.

Code:

void main() {
  double temperature = 30.0; // Example temperature in Celsius 
  if (temperature > 30) {
    print('It\'s a hot day.');
  } else if (temperature >= 20) {
    print('It\'s a pleasant day.');
  } else {
    print('It\'s a cold day.');
  }
}

Code Explanation:

• double temperature = 30.0;: This line declares a variable temperature and assigns it the value 30.0.
• The program checks the temperature using multiple conditions:
  • if (temperature > 30) {: If the temperature is above 30, it prints "It's a hot day."
  • else if (temperature >= 20) {: If the temperature is between 20 and 30 (inclusive), it prints "It's a pleasant day."
  • If neither condition is met, the else block executes, printing "It's a cold day."

Conclusion

Implementing if-else logic in Dart allows you to create dynamic and responsive applications that can make decisions based on user input or other criteria. By understanding how to structure if-else statements, you can effectively handle various scenarios and enhance the interactivity of your programs.