notes-shivam

Journal

7 min read

1. Even or Odd

using System;
class Program {
    static void Main() {
        Console.Write("Enter a number: ");
        int num = int.Parse(Console.ReadLine());
        if (num % 2 == 0) Console.WriteLine("Even!");
        else Console.WriteLine("Odd!");
    }
}

2. Boolean Test for one or other > 10 (but not both)

bool test = (var1 > 10) ^ (var2 > 10);

3. Menu-driven arithmetic with switch and loop

using System;
class Program {
    static void Main() {
        while (true) {
            Console.WriteLine("Menu:\n1.Add\n2.Subtract\n3.Multiply\n4.Divide\n5.Exit");
            Console.Write("Choice: ");
            int ch = int.Parse(Console.ReadLine());
            if (ch == 5) break;
            Console.Write("Num1: "); int a = int.Parse(Console.ReadLine());
            Console.Write("Num2: "); int b = int.Parse(Console.ReadLine());
            switch(ch) {
                case 1: Console.WriteLine(a + b); break;
                case 2: Console.WriteLine(a - b); break;
                case 3: Console.WriteLine(a * b); break;
                case 4: Console.WriteLine(b != 0 ? (a / b).ToString() : "Cannot divide by zero"); break;
                default: Console.WriteLine("Invalid"); break;
            }
        }
    }
}

4. Enum for Days of Week

using System;
enum Days { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday }
class Program {
    static void Main() {
        Console.Write("Enter day number (0-6): ");
        int d = int.Parse(Console.ReadLine());
        if (d>=0 && d<=6) Console.WriteLine((Days)d);
        else Console.WriteLine("Invalid");
    }
}

5. Array input, max and min

using System;
class Program {
    static void Main() {
        Console.Write("Size: ");
        int n=int.Parse(Console.ReadLine());
        int[] arr=new int[n];
        for(int i=0;i<n;i++) arr[i]=int.Parse(Console.ReadLine());
        int max=arr[0], min=arr[0];
        foreach(int x in arr) {
            if(x>max) max=x;
            if(x<min) min=x;
        }
        Console.WriteLine($"Max={max}, Min={min}");
    }
}

6. Reverse String

using System;
class Program {
    static void Main() {
        Console.Write("Enter string: ");
        string s=Console.ReadLine();
        char[] arr=s.ToCharArray();
        Array.Reverse(arr);
        Console.WriteLine($"Original: {s}\nReversed: {new string(arr)}");
    }
}

7. First 10 Prime Numbers

using System;
class Program {
    static bool IsPrime(int n) {
        if(n<2) return false;
        for(int i=2;i*i<=n;i++) if(n%i==0) return false;
        return true;
    }
    static void Main() {
        int count=0, num=2;
        while(count<10) {
            if(IsPrime(num)) {
                Console.Write(num+" ");
                count++;
            }
            num++;
        }
    }
}

8. Factorial with for loop

using System;
class Program {
    static void Main() {
        Console.Write("Enter number: ");
        int n=int.Parse(Console.ReadLine());
        long fact=1;
        for(int i=1;i<=n;i++) fact*=i;
        Console.WriteLine($"Factorial: {fact}");
    }
}

9. Sum of digits using while loop

using System;
class Program {
    static void Main() {
        Console.Write("Enter number: ");
        int n=int.Parse(Console.ReadLine());
        int sum=0;
        while(n!=0) {
            sum+=n%10;
            n/=10;
        }
        Console.WriteLine($"Sum of digits: {sum}");
    }
}

10. Do-while loop sum until negative

using System;
class Program {
    static void Main() {
        int sum=0, num;
        do {
            Console.Write("Enter number (negative to stop): ");
            num=int.Parse(Console.ReadLine());
            if(num>=0) sum+=num;
        } while(num>=0);
        Console.WriteLine($"Sum: {sum}");
    }
}

11. Pyramid pattern

using System;
class Program {
    static void Main() {
        Console.Write("Height: ");
        int h=int.Parse(Console.ReadLine());
        for(int i=1;i<=h;i++) {
            Console.Write(new string(' ', h-i));
            Console.WriteLine(new string('*', 2*i-1));
        }
    }
}

12. Skip printing 5

using System;
class Program {
    static void Main() {
        for(int i=1;i<=10;i++) {
            if(i==5) continue;
            Console.Write(i+" ");
        }
    }
}

13. First 10 Armstrong numbers with break

using System;
class Program {
    static bool IsArmstrong(int n) {
        int sum=0, temp=n;
        while(temp>0) {
            int d=temp%10;
            sum+=d*d*d;
            temp/=10;
        }
        return sum==n;
    }
    static void Main() {
        int count=0, num=1;
        while(count<10) {
            if(IsArmstrong(num)) {
                Console.Write(num+" ");
                count++;
            }
            num++;
        }
    }
}

14. Pass by value and reference demonstration

using System;
class Program {
    static void ModifyValue(int x) { x=100; }
    static void ModifyRef(ref int x) { x=200; }
    static void Main() {
        int a=10;
        Console.WriteLine($"Before: a={a}");
        ModifyValue(a);
        Console.WriteLine($"After ModifyValue: a={a}");
        ModifyRef(ref a);
        Console.WriteLine($"After ModifyRef: a={a}");
    }
}

15. Variable-length parameter method for average

using System;
class Program {
    static double Average(params double[] nums) {
        double sum=0;
        foreach(var n in nums) sum+=n;
        return nums.Length==0 ? 0 : sum/nums.Length;
    }
    static void Main() {
        var avg=Average(1,2,3,4,5);
        Console.WriteLine($"Average: {avg}");
    }
}

16. Boxing and unboxing demo

using System;
class Program {
    static void Main() {
        int a=5;
        object obj = a;   // Boxing
        int b = (int)obj; // Unboxing
        Console.WriteLine($"Boxed: {obj}, Unboxed: {b}");
    }
}

17. Class & Object demonstration

using System;
class Person {
    public string Name;
    public void Greet() {
        Console.WriteLine($"Hello {Name}!");
    }
}
class Program {
    static void Main() {
        Person p = new Person();
        p.Name = "Alice";
        p.Greet();
    }
}

18. Constructor demonstration

using System;
class Person {
    public string Name;
    public Person(string name) {
        Name = name;
    }
}
class Program {
    static void Main() {
        Person p = new Person("Bob");
        Console.WriteLine(p.Name);
    }
}

19. Constructor overloading

using System;
class Person {
    public string Name;
    public int Age;
    public Person() { Name = "Unknown"; Age = 0; }
    public Person(string name) { Name = name; Age = 0; }
    public Person(string name, int age) { Name = name; Age = age; }
}
class Program {
    static void Main() {
        Person p1 = new Person();
        Person p2 = new Person("Carl");
        Person p3 = new Person("Dana", 25);
        Console.WriteLine($"{p1.Name},{p2.Name},{p3.Name} Age: {p3.Age}");
    }
}

20. Copy constructor

using System;
class Person {
    public string Name;
    public int Age;
    public Person(string n, int a) { Name = n; Age = a; }
    public Person(Person p) { Name = p.Name; Age = p.Age; }
}
class Program {
    static void Main() {
        Person p1 = new Person("Eve", 30);
        Person p2 = new Person(p1);
        Console.WriteLine(p2.Name+" "+p2.Age);
    }
}

21. Get & Set properties

using System;
class Person {
    private string name;
    public string Name {
        get { return name; }
        set { name = value; }
    }
}
class Program {
    static void Main() {
        Person p = new Person();
        p.Name = "Frank";
        Console.WriteLine(p.Name);
    }
}

22. Method overloading

using System;
class Calculator {
    public int Add(int a, int b) { return a + b; }
    public double Add(double a, double b) { return a + b; }
}
class Program {
    static void Main() {
        Calculator c = new Calculator();
        Console.WriteLine(c.Add(3,4));
        Console.WriteLine(c.Add(3.5, 4.5));
    }
}

23. Method overriding (Runtime Polymorphism)

using System;
class Animal {
    public virtual void Speak() { Console.WriteLine("Animal speaks"); }
}
class Dog : Animal {
    public override void Speak() { Console.WriteLine("Dog barks"); }
}
class Program {
    static void Main() {
        Animal a = new Dog();
        a.Speak();  // Calls Dog's Speak
    }
}

24. Operator overloading

using System;
class Complex {
    public int Real, Imag;
    public Complex(int r, int i) { Real = r; Imag = i; }
    public static Complex operator+(Complex c1, Complex c2) {
        return new Complex(c1.Real + c2.Real, c1.Imag + c2.Imag);
    }
    public override string ToString() => $"{Real}+{Imag}i";
}
class Program {
    static void Main() {
        Complex c1 = new Complex(1, 2);
        Complex c2 = new Complex(3, 4);
        Complex c3 = c1 + c2;
        Console.WriteLine(c3);
    }
}

25. Interface with method implementation

using System;
interface IShape {
    double Area();
}
class Circle : IShape {
    public double Radius;
    public Circle(double r) { Radius = r; }
    public double Area() => Math.PI * Radius * Radius;
}
class Program {
    static void Main() {
        Circle c = new Circle(3);
        Console.WriteLine(c.Area());
    }
}

26. Abstract class concept

using System;
abstract class Animal {
    public abstract void Sound();
}
class Cat : Animal {
    public override void Sound() => Console.WriteLine("Meow");
}
class Program {
    static void Main() {
        Cat c = new Cat();
        c.Sound();
    }
}

27. Abstract class vs Interface (simple demo)

using System;
abstract class Animal {
    public abstract void Eat();
}
interface IMoveable {
    void Move();
}
class Dog : Animal, IMoveable {
    public override void Eat() { Console.WriteLine("Dog eats"); }
    public void Move() { Console.WriteLine("Dog runs"); }
}
class Program {
    static void Main() {
        Dog d = new Dog();
        d.Eat();
        d.Move();
    }
}

28. System Exception handling

using System;
class Program {
    static void Main() {
        try {
            int a = 10, b = 0;
            Console.WriteLine(a / b);
        } catch (DivideByZeroException ex) {
            Console.WriteLine("Cannot divide by zero!");
        } catch (Exception ex) {
            Console.WriteLine("Error: " + ex.Message);
        }
    }
}

29-33: Windows Forms and ADO.NET (Conceptual)

  • 29. Calculator Windows Form: Use Visual Studio Windows Forms designer to create buttons and textbox, write event handlers for operations.
  • 30. Checkbox events: Handle CheckChanged event to respond to user toggling.
  • 31. Number input with exception handling: Use TextBox and validate input on button click with try-catch.
  • 32. ADO.Net Connection: Create SqlConnection, SqlCommand, open connection to interact with DB.
  • 33. Data Adapter: Use SqlDataAdapter to fill a DataSet/DataTable, update DB from DataSet.

Due to complexity and space, these last items are best developed using Visual Studio with specific setup tutorials.

If needed, more detailed explanations or complete Windows Forms/ADO.NET tutorials for 29-33 can be provided separately. Let me know if you want those!

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