C# Important Codes

1)Write a C program to swap two variables without using a temporary variable?

Swap the value with or without temp

A=10 , B=20

T=A    Give 10 to T

A=B    Give 20 to A

B=T    Give 10 to B

A=A+B  A=30  

B=A-B  B=20

A=A-B A=10

So the moral of the story is, dont try to be smart when writing code to swap variables. Use a temporary variable. It’s not only fool proof, but also easier to understand and maintain

  

2)Two method for factorial? 

1)With recursion

            Console.WriteLine("Enter a number");

            int number = Convert.ToInt32(Console.ReadLine());

            long fact = GetFactorial(number);

            Console.WriteLine("{0} factorial is {1}", number, fact);           

            Console.ReadKey();

        

        private static long GetFactorial(int number)

        {          

            if (number == 0)

            {

                return 1;

            }

            return number * GetFactorial(number-1);

        }

2)Without recursion

            int i, number, fact;

            Console.WriteLine("Enter the Number");

            number = int.Parse(Console.ReadLine());

            fact = number;

            for (i = number - 1; i >= 1; i--)

            {

                fact = fact * i;

            }

            Console.WriteLine("\nFactorial of Given Number is: "+fact);

            Console.ReadLine();

3)Find largest number?

int max = 0;

        List<int> iList = new List<int>();

        iList.Add(100);

        iList.Add(10);

        iList.Add(200);

        iList.Add(35);

        iList.Add(25);

        foreach (int i in iList)

        {

            if (i > max)

                max = i;

        }

4)Generate Random Password?

            string allowedChars = "";

            allowedChars += "1,2,3,4,5,A,B,C,D,E";

            char[] sep = { ',' };

            string[] arr = allowedChars.Split(sep);

            string passwordString = "";

            string temp = "";

            Random rand = new Random();

            for (int i = 0; i < 8; i++)

            {

                temp = arr[rand.Next(0, arr.Length)];

                passwordString += temp;

            }

           string  result = passwordString;

5)Check Prime Numbers

 Console.WriteLine("Enter a number");
            int number = Convert.ToInt32(Console.ReadLine());
            int result = Check_Prime(number);
            if (result == 0)
            {
                Console.WriteLine("{0} is not a prime number", number);
            }
            else
            {
                 Console.WriteLine("{0} is  a prime number", number);
            }            
            Console.Read();

 private static int Check_Prime(int number)
       {
            int i;
            for (i = 2; i <= number - 1; i++)
            {
                if (number % i == 0)
                {
                    return 0;
                }
            }
            if (i == number)
            {
                return 1;
            }
            return 0;
        }

6)Reverse Integer Number?

 Console.WriteLine("Enter a Integer Number");

            int number = Convert.ToInt32(Console.ReadLine());

            int length = number.ToString().Length;

            string reverseNumber = string.Empty;

            for (int i = 0; i < length; i++)

            {

                reverseNumber += (number % 10).ToString();

                number = number / 10;              

            } 

            Console.WriteLine(reverseNumber);

            Console.Read();

7)Duplicate Count in List of numbers?

 int count=0;

   int[] data = { 1, 2, 3, 4, 5, 6, 7, 8, 5, 9, 8, 10, 11, 12, 10, 13, 14, 15, 12, 16, 17, 18, 15, 19, 20 };

   var res = data.GroupBy(t => t);

 foreach(var t in res)

 {

     if (t.Count() > 1)

     {

        Console.WriteLine("The number " + t.Key + " repeated " + t.Count() + " times");

     }

   }

8)Pyramid like this 

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

            int numberoflayer = 5, Space, Number;

            Console.WriteLine("paramid");

            for (int i = 1; i <= numberoflayer; i++) // Total number of layer for pramid

            {

                for (Space = 1; Space <= (numberoflayer - i); Space++)  // Loop For Space

                    Console.Write(" ");

                for (Number = 1; Number <= i; Number++) //increase the value

                    Console.Write("*");

                for (Number = (i - 1); Number >= 1; Number--)  //decrease the value

                    Console.Write("*");

                Console.WriteLine();

            }

            Console.ReadKey();

9)Simple Calculator

int num1;

            int num2;

            string operand;

            float answer;

            Console.Write("Please enter the first number: ");

            num1 = Convert.ToInt32(Console.ReadLine());

            Console.Write("Please enter an operand (+, -, /, *): ");

            operand = Console.ReadLine();

            Console.Write("Please enter the second number: ");

            num2 = Convert.ToInt32(Console.ReadLine());

            switch (operand)

            {

                case "-":

                    answer = num1 - num2;

                    break;

                case "+":

                    answer = num1 + num2;

                    break;

                case "/":

                    answer = num1 / num2;

                    break;

                case "*":

                    answer = num1 * num2;

                    break;

                default:

                    answer = 0;

                    break;

            }

            Console.WriteLine(num1.ToString() + " " + operand + " " + num2.ToString() + " = " + answer.ToString());

            Console.ReadLine();

10)Check if string palindrom or not

string s, revs = "";

            Console.WriteLine(" Enter string");

            s = Console.ReadLine();

            for (int i = s.Length - 1; i >= 0; i--) //String Reverse

            {

                revs += s[i].ToString();

            }

            if (revs == s) // Checking whether string is palindrome or not

            {

                Console.WriteLine("String is Palindrome \n Entered String Was {0} and reverse string is {1}", s, revs);

            }

            else

            {

                Console.WriteLine("String is not Palindrome \n Entered String Was {0} and reverse string is {1}", s, revs);

            }

            Console.ReadKey();