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Project design

Design the structure of the calculator project and write the skeleton code.

Project: Calculator

In this project we will build a calculator step by step. We will add addition, subtraction, multiplication and division functions, handle errors and finally combine them with a menu.

Each lesson builds on the previous one; the initial code embeds the previous solution. You only add the new part. This method is common in real projects.

The first step is to write the program skeleton: void main() and a print that says 'Calculator ready'. In the next lessons we will add functions.

File structure

We will write the calculator in a single .dart file. void main() is the entry point; we add functions below it.

Suggested order: first main, then helper functions (add, subtract, ...). This makes the code easier to read.

Each function does one thing: add only adds, subtract only subtracts. This principle is called 'single responsibility'.

Practice Write the skeleton

Write void main() and add print('Calculator ready') inside. When the program runs we should see this message.

Starter code

main.dart
// Write the calculator skeleton

Sample solution

main.dart
void main() {
  print('Calculator ready');
}

Expected output

Calculator ready

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What will we write first in this project?

  • User input
  • Basic skeleton Correct answer
  • Error handling
  • Menu loop

Explanation: First the skeleton: void main and a print.

2 Entry point

Question 
void ____() { print('Calculator ready'); }
Answer 
void main() { print('Calculator ready'); }

Explanation: main is the program's entry point.

3 Project concepts

Term Meaning
main Entry point
add Addition
subtract Subtraction
print Output

All lessons in Beginner

1 Dart basics

  1. What is Dart?
  2. Your first program
  3. dart run
  4. Comments
  5. String interpolation
  6. Summary - Dart basics

2 Variables

  1. var and type
  2. final
  3. const
  4. late
  5. Null safety
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. bool and String
  4. Type inference
  5. dynamic
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Null-aware operators
  6. Summary - Operators

6 Strings

  1. Creating strings
  2. String interpolation
  3. length and methods
  4. substring
  5. contains and indexOf
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. switch
  4. Pattern matching
  5. Ternary
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. for-in
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Lists

  1. Creating lists
  2. List access
  3. add and remove
  4. length and contains
  5. List methods
  6. Summary - Lists

11 Sets and Maps

  1. Set
  2. Set operations
  3. Map
  4. Map operations
  5. Map iteration
  6. Summary - Sets and Maps

12 Functions

  1. Defining functions
  2. Return values
  3. Arrow functions
  4. Optional parameters
  5. First-class functions
  6. Summary - Functions

13 Null safety in depth

  1. Nullable types
  2. Null-aware operators
  3. The ! operator
  4. late
  5. Null check
  6. Summary - Null safety

14 Class basics

  1. class
  2. Constructor
  3. Instance variables
  4. Methods
  5. this
  6. Summary - Class basics

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. split and join
  2. replace
  3. trim and pad
  4. RegExp
  5. StringBuffer
  6. Summary - Advanced strings

17 Enums

  1. Defining enums
  2. Enum values
  3. Enhanced enums
  4. switch with enum
  5. Enum and patterns
  6. Summary - Enums

18 Exceptions

  1. try/catch
  2. throw
  3. finally
  4. The Exception class
  5. on clause
  6. Summary - Exceptions

19 Async basics

  1. Future
  2. async/await
  3. then
  4. Future.error
  5. Future.wait
  6. Summary - Async basics

20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together