Dart - basics

void main(List<String> args) {
  String firstName = 'John';
  String lastName = 'Jones';
  int age = 36;
  double height = 1.84;

  print(firstName);
  print(lastName);
  print(age);
  print(height);

  double temperature = 20;
  int value = 2;
  String pizza = 'pizza';
  String pasta = 'pasta';

  print('The temperature is ${temperature.toStringAsFixed(0)}C');
  print('$value plus $value makes ${value + value}');
  print('I like $pizza and $pasta');

  print("Today I'm feeling great");
  print('Today I\'m feeling great');

  print('\\');
  print('\$');
  print(r'C:\Windows\system32');

  // Should you prefer 'single' or "double" quotes?
  // Most existing Dart code uses 'single' quotes.
  // Be consistent.

  print("""
  This is an even longer sentence, with some things in
  it.
""");

  // Use multi-line strings to hardcode long chunks of text in your programs.

  String name = 'John';
  print(name.toUpperCase());
  // print -> this is a function
  // .toUpperCase() -> this is a method

  String lovePizza = 'I love pizza.';
  print(lovePizza.contains(pizza));

  // Choose meaningful variable names, based on the values they contain.
  // This makes your code easier to understand.

  int myAge = 36;
  String ageString = myAge.toString();
  print(ageString);

  String ratingString = '4.5';
  double rating = double.parse(ratingString);
  print(rating);

  print(5 ~/ 2); // division operator

  double tempFarenheit = 86;
  double tempCelsius = (tempFarenheit - 32) / 1.8;

  print(
      '${tempFarenheit.toStringAsFixed(0)}F = ${tempCelsius.toStringAsFixed(0)}C');

  int x = 1;
  int y = x++; // Postfix increment operator
  // First: assign x to y
  // Then: increment x

  print('x: $x, y: $y'); // x: 2, y: 1

  int a = 1;
  int b = ++a; // Prefix increment operator
  // First: increment x
  // Then: assign x to y

  print('a: $a, b: $b'); // a: 2, b: 2

  print('');

  int q = 1;
  int w = q++;
  int e = --w;

  print('q: $q, w: $w, e: $e'); // q = 2, w = 1, e = 0

  /*
  bool result = expr1 == expr2
                      !=
                      >=
                      >
                      <=
                      <

  Relational operator are well suited for conditional logic.
  (execute some code only when a condition is true/false)
  */

  print(5 < 2 || 5 < 7); // true
  print(5 < 2 && 5 < 7); // false

  print('');

  String email = 'test@example.com';

  print(email.isNotEmpty && email.contains('@')); // true

  /*
    variable = expr1 ? expr2 : expr3
                true -> [X]
                false        -> [X]
  */

  int someValue = 40;
  String type = someValue > 30 ? 'over 30' : 'under 30';
  print(type);
}

// 결과
John
Jones
36
1.84
The temperature is 20C
2 plus 2 makes 4
I like pizza and pasta
Today I'm feeling great
Today I'm feeling great
\
$
C:\Windows\system32
  This is an even longer sentence, with some things in
  it.

JOHN
true
36
4.5
2
86F = 30C
x: 2, y: 1
a: 2, b: 2

q: 2, w: 0, e: 0
true
false

true
over 30

 

void main(List<String> args) {
  const person = {
    'name': 'John',
    'age': 36,
  };

  if (person['address'] == null) {
    print('address is missing');
  } else {
    print(person['address']);
  }

  int? a;
  int b = 3;

  if (a == null) {
    print(' a is null');
  } else {
    print(a + b);
  }

  print('');

  int x = 10;
  int? maybeValue;

  if (x > 0) {
    maybeValue = x;
  }

  int value = maybeValue!;
  print(value);
  // If we're sure that a nullable variable will wlways have a non-nullable value,
  // we can use the assertion operator.

  // if-null operator

  int? anyValue;
  var somevalue = anyValue == null ? 0 : anyValue;
  print(somevalue);

  int? nullValue;

  print('-----' * 3);
  var thatValue = nullValue ?? 0;
  print(thatValue);

  print('-----' * 3);
  int? nullValue2;
  nullValue2 ??= 0;
  print(nullValue2);

  print('-----' * 3);
  const cities = <String?>['London', 'Paris', null];
  for (var city in cities) {
    if (city != null) {
      print(city);
    }
  }

  print('-----' * 3);
  for (var city in cities) {
    print(city?.toUpperCase());
  }
  // Calling methods on null variables is a very common mistake
  // (easy to forget null checks)
}

/*
null: no value
(can be very useful)

You're likely to work on code written before Null Safety.

Dart without Null Safety -> Runtime error
Dart with Null Safety -> Compile-time error

When to use ! vs ??
-> use ?? if you have a default (or fallback) value
-> use ! if you're sure that your expression/value won't be null at runtime

Should we use type inference or declare types explicitly?
-> initialize variables when you declare them

Type inference and Null Safety work well with each other

Every time you declare a variable, think about whether
it should be nullable or not. 


*/

// 결과
address is missing
 a is null
10
0
---------------
0
---------------
0
---------------
London
Paris
---------------
LONDON
PARIS
null

 

/*
Exercise 1
*/

void main(List<String> args) {
  String name = 'Paul';
  int age = 35;
  int price = 400;

  print("$name, a $age year old, paid \$$price to repair his father's car.");

  print('');

  double tempCityEarly = 18.5;
  double tempCityLate = 25.7;

  print(
      'The average temperature for the day is ${(tempCityEarly + tempCityLate) / 2} degrees celcius.');

  print('');

  String lastName = 'Peters';
  double salary = 1555.35;

  print('$lastName (age $age), Salary: \$$salary pm');

  String carInfo = 'Honda, Ballade, 2006 model, Automatic';

  print(carInfo.toUpperCase());

  String message = 'Hi my friend. You are the bomb!';

  print(message.contains('bomb'));
  print(message.replaceAll(' ', '_'));

  print('');

  int nrOfPeople = 20;
  String nrOfPeopleText = nrOfPeople.toString();
  print(nrOfPeopleText);

  print('');

  double temp = 38.547;
  String tempText = temp.toStringAsFixed(2);
  print(tempText);

  print('');

  String ageText = '20';
  int ageInt = int.parse(ageText);
  print(ageInt);

  print('');

  double nightTemp = 38.67;
  int tempInt = nightTemp.truncate();
  print(tempInt);

  print('');

  int peopleAtShop = 20;
  peopleAtShop--;
  print(peopleAtShop);

  print('');

  int y = 10;
  print(++y); // 11
  print(y); // 11

  int z = 10;
  print(z++); // 10
  print(z); // 11
}

// 결과
Paul, a 35 year old, paid $400 to repair his father's car.

The average temperature for the day is 22.1 degrees celcius.

Peters (age 35), Salary: $1555.35 pm
HONDA, BALLADE, 2006 MODEL, AUTOMATIC
true
Hi_my_friend._You_are_the_bomb!

20

38.55

20

38

19

11
11
10
11

 

void main(List<String> args) {
  int age = 15;
  bool id = true;
  print('Eligibale to rent movies? ${age > 20 && id == true}');

  String type = 'bike';

  print(
      'You will pay ${type == 'bike' ? '\$10' : type == 'Car' ? '\$20' : '\$30'} to enter the Wild Life Park.');

  String email = 'peter@gmail.com';
  print('Valid email address? ${email.contains('@') && email.contains('.')}');

  const firstName = 'Peter';
  const lastName = 'Johnson';
  var fullName = '$firstName $lastName';

  final fullNameLength = fullName.length.toString();
  fullName = 'Peter Pollock'; // no error for assign.
}

// 결과
Eligibale to rent movies? false
You will pay $10 to enter the Wild Life Park.
Valid email address? true

 

void main(List<String> args) {
  const finalMark = 87;

  if (finalMark <= 100 && finalMark >= 80) {
    print('Grade: A');
  } else if (finalMark < 80 && finalMark >= 70) {
    print('Grade: B');
  } else if (finalMark < 70 && finalMark >= 60) {
    print('Grade: C');
  } else if (finalMark < 60 && finalMark >= 50) {
    print('Grade: D');
  } else if (finalMark < 50 && finalMark >= 40) {
    print('Grade: E');
  } else if (finalMark < 40 && finalMark >= 0) {
    print('Grade: F');
  } else {
    print('Invalid mark');
  }
}

// 결과
Grade: A

 

void main(List<String> args) {
// while loop: pre-test loop (runs 0 or more times)

  print('\n******************************\n');
  // 1. Declare and initialize your loop control variable
  int x = 0;

  // 2. Test the loop control variable
  while (x < 3) {
    print('hello world');
    x++; // 3. Change the loop control variable
  }
  print('\n******************************\n');

// do-while loop: post-test loop (runs 1 or more times)

  print('\n******************************\n');
  int y = 0;

  do {
    print('hello world');
    y++;
  } while (y < 3);
  print('\n******************************\n');

// for loop: pre-test loop (runs 0 or more times)
  print('\n******************************\n');
  for (int i = 0; i < 3; i++) {
    print('hello world');
  }
  print('\n******************************\n');
}

// 결과

******************************

hello world
hello world
hello world

******************************


******************************

hello world
hello world
hello world

******************************


******************************

hello world
hello world
hello world

******************************

 

import 'dart:io';

void main(List<String> args) {
  String name;

  do {
    stdout.writeln('Please enter your name: ');
    stdout.writeln('[info] Only enter to exit.');
    name = stdin.readLineSync()!; // sound null safety
    print('Your name is $name');
  } while (name != '');
}

 

import 'dart:io';

// input validation
void main(List<String> args) {
  print('Please enter a number in the range of 1 through 100');
  int number = int.parse(stdin.readLineSync()!);

  while (number < 1 || number > 100) {
    print('The number is not valid!');
    print('Please enter a number in the range of 1 through 100');
    number = int.parse(stdin.readLineSync()!);
  }

  print('$number is valid!');
}

// 결과
Please enter a number in the range of 1 through 100
0
The number is not valid!
Please enter a number in the range of 1 through 100
50
50 is valid!

 

import 'dart:io';

// user controlled
void main(List<String> args) {
  print('How high should I go to square numbers?');

  int nrOfTimes = int.parse(stdin.readLineSync()!);

  print('Value     Value Squared');
  print('--------------------------');

  for (int i = 1; i <= nrOfTimes; i++) {
    print('$i         ${i * i}');
  }
}

// 결과
How high should I go to square numbers?
3
Value     Value Squared
--------------------------
1         1
2         4
3         9

 

import 'dart:io';

void main(List<String> args) {
  int days;
  double sales;
  double totalSales = 0.0;

  print('For how many do you have sales figures?');
  days = int.parse(stdin.readLineSync()!);

  for (int count = 1; count <= days; count++) {
    print('Enter the sales for day $count');

    sales = double.parse(stdin.readLineSync()!);
    totalSales += sales;
  }

  print('the total sales for $days are R${totalSales.toStringAsFixed(2)}');
}

// 결과
Enter the sales for day 8
1
Enter the sales for day 9
2
Enter the sales for day 10
23
the total sales for 10 are R51.00

 

// sentinel values

import 'dart:io';

void main(List<String> args) {
  int value;
  int doubleValue;

  print('Please enter a value to double or 0 to stop');
  value = int.parse(stdin.readLineSync()!);

  while (value != 0) {
    doubleValue = value * 2;
    print('$value doubles is $doubleValue');
    value = int.parse(stdin.readLineSync()!);
  }
}

// 결과
Please enter a value to double or 0 to stop
10
10 doubles is 20
2
2 doubles is 4
0

 

import 'dart:io';

void main(List<String> args) {
  print('Please enter your email address');
  String email = stdin.readLineSync()!;

  while (!email.contains('@') || !email.contains('.')) {
    print('Email not valid!');
    print('Please re-enter your email address...');
    email = stdin.readLineSync()!;
  }
  print('$email is valid email address.');
}

// 결과
Please enter your email address
my@example
Email not valid!
Please re-enter your email address...
myemail.com
Email not valid!
Please re-enter your email address...
myemail address
Email not valid!
Please re-enter your email address...
my@example.com
my@example.com is valid email address.

 

import 'dart:io';

void main(List<String> args) {
  int choice;

  do {
    print('\n');
    print('Make your choice:');
    print('1. McDonald\'s Fries');
    print('2. McDonald\'s Big Mac');
    print('3. McDonald\'s Breakfast Muffin');
    print('4. Exit');
    print('\n');

    choice = int.parse(stdin.readLineSync()!);
    switch (choice) {
      case 1:
        print('You chose fries');
        break;
      case 2:
        print('You chose big mac');
        break;
      case 3:
        print('You chose breakfast muffin');
        break;
      case 4:
        print('Good bye');
        break;
      default:
        print('Invalid choice! Please try again!');
    }
  } while (choice != 4);
}

// 결과
Make your choice:
1. McDonald's Fries
2. McDonald's Big Mac
3. McDonald's Breakfast Muffin
4. Exit


1
You chose fries


Make your choice:
1. McDonald's Fries
2. McDonald's Big Mac
3. McDonald's Breakfast Muffin
4. Exit


6
Invalid choice! Please try again!


Make your choice:
1. McDonald's Fries
2. McDonald's Big Mac
3. McDonald's Breakfast Muffin   
4. Exit


4
Good bye