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+import 'dart:math';
+
+
+// A Function that takes two parameter and return their sum
+int sum(int a, int b) {
+  return a + b;
+}
+
+// Function that calculate the factorial of a given number
+int factorial(int n) {
+  if (n == 0 || n == 1) {
+    return 1;
+  } else {
+    return n * factorial(n - 1);
+  }
+}
+
+// Function that checks is a number is a prime
+bool isPrime(int number) {
+  if (number <= 1) {return false;
+  } else {
+    return true;
+  }}
+
+
+// Function that converts Celsius to Fahrenheit
+double celsiusToFahrenheit(double celsius) {
+  return (celsius * 9 / 5) + 32;
+}
+
+// A function that reverse a string
+class StringManipulator {
+  static String reverseString(String inputString) {
+    List<String> characters = inputString.split('');
+    characters = characters.reversed.toList();
+    return characters.join('');
+  }
+}
+
+//A Class named Person
+class Person {
+  String name;
+  int age;
+
+  Person(this.name, this.age);
+
+//Method
+  void displayInfo() {
+    print("Name: $name");
+    print("Age: $age");
+  }
+}
+
+// A Class named  Rectangle
+class Rectangle {
+  double length;
+  double width;
+
+  Rectangle(this.length, this.width);
+
+//Method
+  double calculateArea() {
+    return length * width;
+  }
+}
+
+// A Class named Cirle
+
+class Circle {
+  double radius;
+
+  Circle(this.radius);
+
+//Method
+  double calculateCircumference() {
+    return 2 * pi * radius;
+  }
+}
+
+
+//A Class named Bank Account
+class BankAccount {
+  double balance;
+
+  BankAccount(this.balance);
+
+//Method
+  void deposit(double amount) {
+    if (amount > 0) {
+      balance += amount;
+      print("Deposited: $amount units");
+    } else {
+      print("deposit amount is invalid");
+    }
+  }
+
+  void withdraw(double amount) {
+    if (amount > 0 && amount <= balance) {
+      balance -= amount;
+      print("Withdrawn: $amount units");
+    } else {
+      print("insufficient funds");
+    }
+  }
+
+  void checkBalance() {
+    print("Account Balance: $balance units");
+  }
+}
+
+
+//A Class named Student
+class Student {
+  String name;
+  int age;
+  double grade;
+
+  Student(this.name, this.age, this.grade);
+
+//Method
+  bool isPassed() {
+    return grade >= 50.0;
+  }
+}
+
+
+// A Class named Calculator
+class Calculator {
+  double sum(double num1, double num2) {
+    return num1 + num2;
+  }
+
+  double subtract(double num1, double num2) {
+    return num1 - num2;
+  }
+
+  double multiply(double num1, double num2) {
+    return num1 * num2;
+  }
+
+  double divide(double num1, double num2) {
+    if (num2 != 0) {
+      return num1 / num2;
+    } else {
+      print("Error: Division by zero");
+      return double.nan;
+    }
+  }
+}
+
+
+// A Class named Car
+class Car {
+  bool _isStarted = false;
+  double _fuelLevel = 0.0; // The level of Fuel in liters
+
+//Method
+  void start() {
+    if (!_isStarted) {
+      _isStarted = true;
+      print("Car started");
+    } else {
+      print("Car is already started");
+    }
+  }
+
+  void stop() {
+    if (_isStarted) {
+      _isStarted = false;
+      print("Car stopped");
+    } else {
+      print("Car is already stopped");
+    }
+  }
+
+  void checkFuelLevel() {
+    print("Fuel level: $_fuelLevel liters");
+  }
+
+  void refuel(double amount) {
+    if (amount > 0) {
+      _fuelLevel += amount;
+      print("Refueled: $amount liters");
+    } else {
+      print("Invalid fuel amount");
+    }
+  }
+}
+
+
+// A Function that finds the Maximum element in alist of integer
+int findMaxElement(List<int> numbers) {
+  if (numbers.isEmpty) {
+    throw ArgumentError("List is empty");
+  }
+
+  int maxElement = numbers[0];
+
+  for (int i = 1; i < numbers.length; i++) {
+    if (numbers[i] > maxElement) {
+      maxElement = numbers[i];
+    }
+  }
+
+  return maxElement;
+}
+
+// A Class Employee
+class Employee {
+  String name;
+  double salary;
+
+  Employee(this.name, this.salary);
+
+//Method
+  void giveBonus(double bonusAmount) {
+    if (bonusAmount > 0) {
+      salary += bonusAmount;
+      print("$name received a bonus of $bonusAmount");
+    } else {
+      print("Invalid bonus amount");
+    }
+  }
+}
+
+
+// A Function and Class that calculates the area of a Triangle
+class Triangle {
+  double base;
+  double height;
+
+  Triangle(this.base, this.height);
+
+//Method
+  double calculateArea() {
+    return 0.5 * base * height;
+  }
+}
+
+double calculateTriangleArea(double base, double height) {
+  Triangle triangle = Triangle(base, height);
+  return triangle.calculateArea();
+}
+
+
+// A Function that finds a Square root oa a number
+
+double findSquareRoot(double number) {
+  return sqrt(number);
+}
+
+
+// Function that generates a fibonacci numbers up to a specific limit
+List<int> generateFibonacciNumbers(int limit) {
+  List<int> fibonacciNumbers = [];
+
+  int a = 0, b = 1;
+  while (a <= limit) {
+    fibonacciNumbers.add(a);
+    int temp = a + b;
+    a = b;
+    b = temp;
+  }
+
+  return fibonacciNumbers;
+}
+
+// A Function tha determine a leap year
+bool isLeapYear(int year) {
+  if (year % 4 == 0) {
+    if (year % 100 == 0) {
+      if (year % 400 == 0) {
+        return true; // If the year is divisible by 400, it is a leap year
+      } else {
+        return false; // If the year is divisible by 100 but not by 400, it is not a leap year
+      }
+    } else {
+      return true; // If the year is divisible by 4 but not by 100, it is a leap year
+    }
+  } else {
+    return false; // If the year is not divisible by 4, it is not a leap year
+  }
+}
+
+
+// Recursive function that compute a factorial number
+int factorials(int n) {
+  if (n == 0 || n == 1) {
+    return 1;
+  } else {
+    return n * factorial(n - 1);
+  }
+}
+
+
+// A function that returns a list of integers with even numbers only
+List<int> getEvenNumbers(List<int> numbers) {
+  List<int> evenNumbers = [];
+
+  for (int number in numbers) {
+    if (number % 2 == 0) {
+      evenNumbers.add(number);
+    }
+  }
+
+  return evenNumbers;
+}
+
+void main() {
+
+  // No 1
+  int result = sum(18, 20);
+  print("The sum is $result");
+
+  //No  2
+  int number = 5;
+  int output = factorial(number);
+  print("The factorial of $number is $output");
+
+  //No  3
+  int num1 = 27;
+  print("$num1 is ${isPrime(num1) ? 'a prime' : 'not a prime' } number");
+
+
+  //No 4
+  double celsiusTemperature = 70.0;
+  double fahrenheitTemperature = celsiusToFahrenheit(celsiusTemperature);
+  print("$celsiusTemperature°C is $fahrenheitTemperature°F in Fahreheit");
+
+
+  //No 5
+  String originalString = "Thank, God";
+  String reversedString = StringManipulator.reverseString(originalString);
+  print("Original string: $originalString");
+  print("Reversed string: $reversedString");
+
+
+  //No 6
+  Person person1 = Person("Goodnews", 18);
+  person1.displayInfo();
+
+
+  // No  7
+  Rectangle rectangle = Rectangle(15.0, 10.0);
+  double area = rectangle.calculateArea();
+  print("The Area of the rectangle is $area square units"); 
+
+
+  // No 8 
+  Circle circle = Circle(25.0);
+  double circumference = circle.calculateCircumference();
+  print("The Circumference of the circle is $circumference units"); 
+
+
+  // No 9
+  BankAccount account = BankAccount(100000.0);
+
+  account.checkBalance(); 
+
+  account.deposit(34000.0); 
+  account.checkBalance(); 
+
+  account.withdraw(10000.0); 
+  account.checkBalance(); 
+
+  account.withdraw(50000.0);
+  account.checkBalance();
+
+
+  // No 10
+  Student student1 = Student("Goodnews", 20, 95.0);
+  print("${student1.name} ${student1.isPassed() ? 'passed' : 'failed'}");
+
+
+  //No 11
+  Calculator calculator = Calculator();
+
+  double resultAdd = calculator.sum(10.0, 30.0);
+  print("Addition: $resultAdd"); 
+
+  double resultSubtract = calculator.subtract(45.0, 20.0);
+  print("Subtraction: $resultSubtract");
+
+  double resultMultiply = calculator.multiply(7.0, 5.0);
+  print("Multiplication: $resultMultiply");
+
+
+// No 12
+Car car = Car();
+
+car.start(); 
+car.checkFuelLevel();
+
+car.refuel(50.0); 
+car.checkFuelLevel();
+
+car.stop();
+
+
+//No 13
+List<int> numbers = [10, 7, 2, 8, 9, 5];
+int max = findMaxElement(numbers);
+print("Maximum element in the list: $max");
+
+
+//No  14
+Employee employee = Employee("Walter Goodnews", 50000000.0);
+print("Original salary of ${employee.name} is ${employee.salary}"); 
+
+employee.giveBonus(6000.0); 
+print("The New salary of ${employee.name} is ${employee.salary}"); 
+
+
+//No 15
+double base = 6.0;
+double height = 8.0;
+double areas = calculateTriangleArea(base, height);
+print("Area of the triangle with base $base and height $height is $areas square units");
+
+
+//No 16
+double num2 = 25.0;
+double squareRoot = findSquareRoot(num2);
+print("The Square root of $num2 is $squareRoot"); 
+
+
+//No 17
+ int limit = 10;
+ List<int> fibonacciList = generateFibonacciNumbers(limit);
+ print("Fibonacci numbers up to $limit is $fibonacciList");
+
+
+ //No 18
+ int year1 = 2020;
+  print("$year1 is ${isLeapYear(year1) ? 'a leap' : 'not a leap'} year"); 
+
+  int year2 = 2021;
+  print("$year2 is ${isLeapYear(year2) ? 'a leap' : 'not a leap'} year"); 
+
+
+  //No 19
+  int nums = 15;
+  int results = factorial(nums);
+  print("The Factorial of $nums is $results"); 
+
+
+  //No 20
+  List<int> num = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15];
+  List<int> evenNumbers = getEvenNumbers(num);
+  print("Original list: $num");
+  print("Even numbers: $evenNumbers");
+}
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