#Lecture 004 — Your First Program: Hello World

We write a program from an empty file and explain every symbol in it.

Contents

Prerequisites · Objectives · Lesson · Code Examples · Common Mistakes · Practice Questions · Answers · Takeaways

#Prerequisites

Lecture 003: DartPad open, or a project in IntelliJ.

#Learning Objectives

• Write and run a program from scratch
• Explain void, main, (), {}, print and ;
• Print several lines

#1. The Smallest Program

In DartPad, or in bin/main.dart in your project, type:

void main() {
  print('Hello, World!');
}

Run it (▶ in IntelliJ, Run in DartPad, or dart run bin/main.dart):

Hello, World!

#2. Every Part Explained

#3. Top to Bottom

Instructions inside main run in order, one after another:

void main() {
  print('First');
  print('Second');
  print('Third');
}

First
Second
Third

#Code Examples

#Example 1 — Introduce Yourself

void main() {
  print('Hello, World!');
  print('My name is Hamza.');
  print('I am learning Dart.');
  print("Today is Day 2.");
}

Output

Hello, World!
My name is Hamza.
I am learning Dart.
Today is Day 2.

Single '...' and double "..." quotes both make strings. Pick one style and stick to it — Dart's own style uses single quotes.

#Common Beginner Mistakes

1. Forgetting the ; — print('Hi') alone gives Expected ';' after this. Every instruction ends with a semicolon.

2. Mismatched quotes — print('Hi"); starts with ' and ends with ". Use the same kind on both sides.

3. Capital letters — Print or Main are different names from print and main. Dart is case-sensitive.

4. Code outside main — a print(...) line outside the { } of main is an error.

#Practice Questions

1. Which function does every Dart program start from?
2. What does void mean before main?
3. What does ; do?
4. Write a program that prints your name and your city on two lines.

#Practice Answers

1. main.
2. main returns no value.
3. Ends an instruction.
4. void main() { print('Ali'); print('Karachi'); }

#Key Takeaways

• A Dart program starts at void main() { ... }.
• print writes one line of text.
• Instructions run top to bottom and end with ;.
• Dart is case-sensitive: print, not Print.