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Basic Syntax and Structure

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In this section, we will cover the fundamental syntax and structure of Dart programs. Understanding these basics is crucial for writing efficient and error-free Dart code.

Key Concepts

  1. Dart Program Structure
  2. Comments
  3. Variables and Data Types
  4. Functions
  5. Control Flow Statements
  6. Error Handling

  1. Dart Program Structure

A Dart program typically consists of:

  • Libraries: Collections of related classes and functions.
  • Classes: Blueprints for creating objects.
  • Functions: Blocks of code that perform specific tasks.
  • Variables: Containers for storing data values.

Example

// Importing a library
import 'dart:math';

// Defining a class
class Circle {
  // Class properties
  double radius;

  // Constructor
  Circle(this.radius);

  // Method to calculate area
  double area() {
    return pi * radius * radius;
  }
}

// Main function
void main() {
  // Creating an object of Circle
  Circle circle = Circle(5.0);
  print('The area of the circle is ${circle.area()}');
}

Explanation

  • Importing Libraries: import 'dart:math'; imports the math library.
  • Class Definition: class Circle defines a class named Circle.
  • Constructor: Circle(this.radius); initializes the radius property.
  • Method: double area() calculates the area of the circle.
  • Main Function: void main() is the entry point of the program.

  1. Comments

Comments are used to explain code and are ignored by the compiler.

  • Single-line comments: Use //
  • Multi-line comments: Use /* ... */
  • Documentation comments: Use /// or /** ... */

Example

// This is a single-line comment

/*
This is a
multi-line comment
*/

/// This is a documentation comment
/// for a function
void exampleFunction() {
  // Function code here
}

  1. Variables and Data Types

Variables store data values. Dart is a statically-typed language, meaning you must declare the type of a variable.

Common Data Types

Data Type Description Example
int Integer values int age = 30;
double Floating-point values double height = 5.9;
String Sequence of characters String name = 'John';
bool Boolean values (true/false) bool isActive = true;
var Type inferred by the compiler var score = 100;

Example

void main() {
  int age = 30;
  double height = 5.9;
  String name = 'John';
  bool isActive = true;
  var score = 100; // Type inferred as int

  print('Name: $name, Age: $age, Height: $height, Active: $isActive, Score: $score');
}

  1. Functions

Functions are blocks of code that perform specific tasks. They can take parameters and return values.

Syntax

returnType functionName(parameter1, parameter2, ...) {
  // Function body
  return value;
}

Example

int add(int a, int b) {
  return a + b;
}

void main() {
  int result = add(5, 3);
  print('The sum is $result');
}

  1. Control Flow Statements

Control flow statements determine the flow of execution in a program.

If-Else Statement

void main() {
  int number = 10;

  if (number > 0) {
    print('Positive number');
  } else if (number < 0) {
    print('Negative number');
  } else {
    print('Zero');
  }
}

For Loop

void main() {
  for (int i = 0; i < 5; i++) {
    print('i = $i');
  }
}

While Loop

void main() {
  int i = 0;
  while (i < 5) {
    print('i = $i');
    i++;
  }
}

  1. Error Handling

Dart provides a way to handle errors using try, catch, and finally blocks.

Example

void main() {
  try {
    int result = 10 ~/ 0; // Integer division by zero
    print(result);
  } catch (e) {
    print('Error: $e');
  } finally {
    print('This is always executed');
  }
}

Practical Exercises

Exercise 1: Basic Dart Program

Task: Write a Dart program that defines a class Rectangle with properties length and width, and a method area that calculates the area of the rectangle. Create an object of Rectangle and print the area.

Solution:

class Rectangle {
  double length;
  double width;

  Rectangle(this.length, this.width);

  double area() {
    return length * width;
  }
}

void main() {
  Rectangle rectangle = Rectangle(5.0, 3.0);
  print('The area of the rectangle is ${rectangle.area()}');
}

Exercise 2: Control Flow

Task: Write a Dart program that takes an integer input and prints whether the number is even or odd.

Solution:

void main() {
  int number = 4;

  if (number % 2 == 0) {
    print('$number is even');
  } else {
    print('$number is odd');
  }
}

Summary

In this section, we covered the basic syntax and structure of Dart programs, including:

  • Program structure
  • Comments
  • Variables and data types
  • Functions
  • Control flow statements
  • Error handling

Understanding these basics will help you write more complex Dart programs as you progress through the course. In the next module, we will dive deeper into Dart basics, starting with variables and data types.

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