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Putting it together

Combine all parts into a working calculator.

Putting it together: menu loop

In the final step we will combine all parts and add a menu loop. A while loop makes the program show the menu again and again.

Structure: var count = 0; while (count < 3) { print('Menu $count'); count++; }. This prints 'Menu 0', 'Menu 1', 'Menu 2'.

In a real calculator the loop reads user input and acts on the choice. Here we will finish with a simple counted loop; reading input is covered in later lessons.

Practice Add the menu loop

Inside main, after the try/catch, add a while loop. Start with var count = 0;; loop with while (count < 3); inside it put print('Menu $count') and count++.

Starter code

main.dart
void main() {
  print('Calculator ready');
  print(add(3, 4));
  print(subtract(10, 3));
  print(multiply(5, 6));
  print(divide(10, 4));
  try {
    throw Exception('Invalid input');
  } catch (e) {
    print('Error: $e');
  }
  // Add a menu with a while loop
}

int add(int a, int b) => a + b;
int subtract(int a, int b) => a - b;
int multiply(int a, int b) => a * b;
double divide(int a, int b) => a / b;

Sample solution

main.dart
void main() {
  print('Calculator ready');
  print(add(3, 4));
  print(subtract(10, 3));
  print(multiply(5, 6));
  print(divide(10, 4));
  try {
    throw Exception('Invalid input');
  } catch (e) {
    print('Error: $e');
  }
  var count = 0;
  while (count < 3) {
    print('Menu $count');
    count++;
  }
}

int add(int a, int b) => a + b;
int subtract(int a, int b) => a - b;
int multiply(int a, int b) => a * b;
double divide(int a, int b) => a / b;

Expected output

Calculator ready
7
7
30
2.5
Error: Exception: Invalid input
Menu 0
Menu 1
Menu 2

Practice Final calculator

In this final task write the whole program yourself. Inside void main have print('Calculator ready'), an add(3, 4) call, a try/catch and a while loop. Also define the add function.

Starter code

main.dart
// Write the calculator from scratch

Sample solution

main.dart
void main() {
  print('Calculator ready');
  print(add(3, 4));
  try {
    throw Exception('Invalid input');
  } catch (e) {
    print('Error: $e');
  }
  var count = 0;
  while (count < 3) {
    print('Menu $count');
    count++;
  }
}

int add(int a, int b) => a + b;

Expected output

Calculator ready
7
Error: Exception: Invalid input
Menu 0
Menu 1
Menu 2

Questions and answers

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

1 Which is the best structure for a menu loop?

  • for loop
  • while loop Correct answer
  • if condition
  • switch

Explanation: while repeats as long as the condition is true.

2 Loop keyword

Question 
____ (true) { showMenu(); }
Answer 
while (true) { showMenu(); }

Explanation: while sets up a conditional loop.

3 Project parts

Term Meaning
while Loop
add Addition
try/catch Error catching
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