Swap neighbor character in string in c#:

            string str = "TAPAN";
            Console.WriteLine("Before Swaping :"+str);
            string str1 = "";
            Console.Write("After Swaping :");
            for (int i = 0; i < str.Length; i = i + 2)
            {
                int j = 0;
                if (str.Length % 2 != 0 && i == str.Length - 1) { j = 1; }
                str1 += j == 0 ? str[i + 1].ToString() : "";
                str1 += str[i].ToString();
            }
            Console.WriteLine(str1);

check number is Prime or not Prime in c#.

            int number = 13;
            int pr = 0;
            for (int i = 2; i < number; i++)
            {
                if (number % i == 0)
                {
                    pr++;
                }
            }
            if (pr > 0)
            {
                Console.WriteLine("No is not Prime");
            }
            else
            {
                Console.WriteLine("No is Prime");
            }

Fibonacci series in c# :

            int kk = 1, jj = 0, yy = 0;
            Console.Write(yy);
            for (int i = 0; i < 10; i++)
            {
                jj = kk;
                kk = yy;
                yy = kk + jj;
                Console.Write("," + yy);
            }

Factorial Of Given Number in c#:

            int factnumber = 6;
            int fact = 1;
            for (int i = factnumber; i > 0; i--)
            {
                fact = fact * i;
            }
            Console.WriteLine("\nFact :" + fact);

1. Sum OF Given number c#.

2. Reverse  a number c#.

3. Count 1 in given number c#.

string getnumber = "";
            int sum = 0;
            Console.Write("Enter No :");
            getnumber = Console.ReadLine();
            int one = 0;
            for (int i = 0; i < getnumber.Length; i++)
            {
                string s = getnumber[i].ToString();
                if (s == "1")
                {
                    one++;
                }
                sum = sum + Convert.ToInt32(s);
            }

            Console.WriteLine("Sum Of Digits Of No :"+sum);
            Console.WriteLine("No of One :" + one);
            Console.Write("Reverse No.");
            for (int i = getnumber.Length - 1; i >= 0; i--)
            {
                Console.Write(getnumber[i]);
            }

Csharp program to print a Rhombus:

for (int i = 1; i <= 5; i++)
            {
                for (int j = i - 1; j > 1; j--)
                {
                    Console.Write(j);
                }
                for (int j = 1; j < i; j++)
                {
                    Console.Write(j);
                }
                Console.WriteLine();
            }
            for (int i = 4; i > 0; i--)
            {
                for (int j = i - 1; j > 1; j--)
                {
                    Console.Write(j);
                }
                for (int j = 1; j < i; j++)
                {
                    Console.Write(j);
                }
                Console.WriteLine();
            }

output : 

1
212
32123
4321234
32123
212
1

Csharp program to print Rhombus of numbers:

 int nu = 5;
            for (int i = 1; i <= nu; i++)
            {
                for (int j = 1; j < i; j++)
                {
                    Console.Write(j);
                }
                for (int j = i - 2; j > 0; j--)
                {
                    Console.Write(j);
                }
                Console.WriteLine();
            }

Output :
1
121
12321
1234321