Chapter 09 Methods

Task-01-Send Greeting

using System;

namespace Task_01_Send_Greeting
{
    public class SendGreeting
    {
        public static void Main(string[] args)
        {
            Console.Write("Enter a name: ");
            string name = Console.ReadLine();
            PrintGreeting(name);
        }

        static void PrintGreeting(string name)
        {
            Console.WriteLine("Hello, {0}!", name);
        }
    }
}

Task-02-Find Biggest Number

using System;

namespace Task_02_Find_Biggest_Number
{
    class FindBiggestNumber
    {
        static void Main(string[] args)
        {
            Console.Write("Enter the first number: ");
            string input = Console.ReadLine();
            int number1;

            if (int.TryParse(input, out number1))
            {
                number1 = int.Parse(input);
            }
            else
            {
                Console.WriteLine("Invalid number");
                return;
            }

            Console.Write("Enter the second number: ");
            input = Console.ReadLine();
            int number2;

            if (int.TryParse(input, out number2))
            {
                number2 = int.Parse(input);
            }
            else
            {
                Console.WriteLine("Invalid number");
                return;
            }

            Console.Write("Enter the third number: ");
            input = Console.ReadLine();
            int number3;

            if (int.TryParse(input, out number3))
            {
                number3 = int.Parse(input);
            }
            else
            {
                Console.WriteLine("Invalid number");
                return;
            }

            Console.WriteLine(GetMax(number1, number2, number3));
        }

        static int GetMax(int num1, int num2, int num3)
        {
            int maxNumber = Math.Max(num1, Math.Max(num2, num3));
            return maxNumber;
        }
    }
}

Task-03-Get Last Number

using System;

namespace Task_03_Get_Last_Number
{
    class Program
    {
        static string GetLastNumber(long number)
        {
            string numInDigits;
            number = Math.Abs(number);

            switch (number % 10)
            {
                case 0:
                    numInDigits = "zero";
                    break;
                case 1:
                    numInDigits = "one";
                    break;
                case 2:
                    numInDigits = "two";
                    break;
                case 3:
                    numInDigits = "three";
                    break;
                case 4:
                    numInDigits = "four";
                    break;
                case 5:
                    numInDigits = "five";
                    break;
                case 6:
                    numInDigits = "six";
                    break;
                case 7:
                    numInDigits = "seven";
                    break;
                case 8:
                    numInDigits = "eight";
                    break;
                case 9:
                    numInDigits = "nine";
                    break;
                default:
                    Console.WriteLine("error");
                    return null;
            }

            return numInDigits;
        }

        static void Main(string[] args)
        {
            Console.Write("Enter a number : ");
            string input = Console.ReadLine();
            long number;

            if (long.TryParse(input, out number))
            {
                number = long.Parse(input);
            }
            else
            {
                Console.WriteLine("Invalid number.");
                return;
            }

            Console.Write("The last digit is: ");
            Console.WriteLine(GetLastNumber(number));
        }
    }
}

Task-04-Find Repeating Number

using System;

namespace Task_04_Find_Repeating_Number
{
    class FindRepeatingNumber
    {
        static int CountRepeatingNumber(int[] numbers, int num)
        {
            int count = 0;

            for (int i = 0; i < numbers.Length; i++)
            {
                if (numbers[i] == num)
                {
                    count++;
                }
            }

            return count;          
        }

        static void Main(string[] args)
        {
            Console.Write("Enter the number to find: ");
            string input = Console.ReadLine();
            int numberToFind;

            if (int.TryParse(input, out numberToFind))
            {
                numberToFind = int.Parse(input);
            }
            else
            {
                Console.WriteLine("Invalid number.");
                return;
            }
            
            int[] numbers = new int[] { 10, 3, 5, -1, 0, 12, 8, 10, 3, 5, -1, 0, 12, 8 };
            Console.WriteLine("The number {0} has been foud {1} times in the array",
                       numberToFind, CountRepeatingNumber(numbers, numberToFind));
        }
    }
}

Task-05-Check Element In Array

using System;

namespace Task_05_Check_Element_In_Array
{
    class CheckElementInArray
    {
        static string CheckElement(int index, int[] array)
        {
            if (index == 0)
            {
                if (array[index] < array[index + 1])
                {
                    return "lower";
                }
                else if (array[index] > array[index + 1])
                {
                    return "bigger";
                }
                else
                {
                    return "equal";
                }
            }
            else if (index == array.Length - 1)
            {
                if (array[index] < array[index - 1])
                {
                    return "lower";
                }
                else if (array[index] > array[index - 1])
                {
                    return "bigger";
                }
                else
                {
                    return "equal";
                }
            }
            else
            {
                if (array[index] < array[index + 1] && array[index] < array[index - 1])
                {
                    return "lower";
                }
                else if (array[index] > array[index + 1] && array[index] > array[index - 1])
                {
                    return "bigger";
                }
                else
                {
                    return "equal";
                }
            }
        }

        static void PrintElement(string attitude)
        {
            Console.WriteLine("The element is {0} to its neighbours", attitude);
        }

        static void Main(string[] args)
        {
            Console.Write("Enter an element number (1 - 20):");
            string input = Console.ReadLine();
            int element;

            if (int.TryParse(input, out element))
            {
                element = int.Parse(input);
            }
            else
            {
                Console.WriteLine("Invalid number.");
                return;
            }

            int[] array = new int[] { 9, 8, 5, 20, 13, 7, 6, 18, 11, 19, 1, 3, 12, 2, 16, 15, 4, 10, 14, 17 };
            PrintElement(CheckElement(element, array));
        }
    }
}

Task-06-Find First Bigger Element

using System;

namespace Task_06_Find_First_Bigger_Element
{
    class FindFirstBiggerElement
    {
        static int FindElement(int[] arr)
        {
            int index = -1;

            for (int i = 0; i < arr.Length; i++)
            {
                if (i == 0 && arr[i] > arr[i + 1])
                {
                    index = arr[i];
                    break;
                }
                else if (i > 0 && i < arr.Length - 1 && (arr[i] > arr[i + 1] && arr[i] > arr[i - 1]))
                {
                    index = arr[i];
                    break;
                }
                else if (i == arr.Length - 1 && arr[i] > arr[i - 1])
                {
                    index = arr[i];
                    break;                    
                }
            }

            return index;
        }

        static void Main(string[] args)
        {
            int[] array = new int[] { 8, 8, 5, 20, 13, 7, 6, 18, 11, 19, 1, 3, 12, 2, 16, 15, 4, 10, 14, 17 };
            Console.Write("The first bigger element is: ");
            Console.WriteLine(FindElement(array));
        }
    }
}

Task-07-Reverse Number

using System;

namespace Task_07_Reverse_Number
{
    class ReverseNumber
    {
        static int ReverseNum(int number)
        {
            int reverse = 0;
            int sign = number > -1 ? 1 : -1;
            number = Math.Abs(number);

            while (number > 0)
            {
                reverse += (number % 10);
                number /= 10;
                reverse *= 10;
            }

            reverse /= 10 * sign;
            return reverse;
        }

        static void Main(string[] args)
        {
            Console.Write("Enter a number: ");
            string input = Console.ReadLine();
            int number;

            if (int.TryParse(input, out number))
            {
                number = int.Parse(input);
            }
            else
            {
                Console.WriteLine("Invalid number;");
                return;
            }

            int reversedNumber = ReverseNum(number);
            Console.WriteLine(reversedNumber);
        }
    }
}

Task-08-Add Two Numbers

using System;
using System.Collections.Generic;
using System.IO;

namespace Task_08_Add_Two_Numbers
{
    class AddTwoNumbers
    {
        static void Main(string[] args)
        {
            Stream buffer = Console.OpenStandardInput(10000);
            Console.SetIn(new StreamReader(buffer, Console.InputEncoding, false, 10000));

            Console.Write("Enter the first number: ");
            string firstInput = Console.ReadLine();
            Console.Write("Enter the second number: ");
            string secondInput = Console.ReadLine();

            if (firstInput.Length < secondInput.Length)
            {
                string swap = firstInput;
                firstInput = secondInput;
                secondInput = swap;
            }

            List<int> number1 = new List<int>(GetNumber(firstInput));
            List<int> number2 = new List<int>(GetNumber(secondInput));

            if (number1.Count != firstInput.Length || number2.Count != secondInput.Length)
            {
                Console.WriteLine("Invalid number.");
                return;
            }

            List<int> sumNumbers = SumNumbers(number1, number2);
            sumNumbers.Reverse();           
            Console.WriteLine("The sum is: ");
            sumNumbers.ForEach(Console.Write);
            Console.WriteLine();
        }

        private static List<int> SumNumbers(List<int> number1, List<int> number2)
        {
            int plusOne = 0;
            List<int> result = new List<int>();

            for (int i = number1.Count - 1, j = number2.Count - 1; i > -1; i--, j--)
            {
                int num1 = number1[i];
                int num2 = j > -1 ? number2[j] : 0;
                int sum = num1 + num2 + plusOne;
                result.Add(sum % 10);
                plusOne = sum / 10;
            }

            if (plusOne == 1)
            {
                result.Add(plusOne);
            }

            return result;
        }

        private static List<int> GetNumber(string strNumber)
        {
            List<int> newList = new List<int>();

            for (int i = 0; i < strNumber.Length; i++)
            {
                if ((strNumber[i] - 48) > -1 && (strNumber[i] - 48) < 10)
                {
                    int num = (strNumber[i] - 48);
                    newList.Add(num);
                }
            }

            return newList;
        }
    }
}

Task-09-Find Biggest Element And Sort Array

using System;

namespace Task_09_Find_Biggest_Element_And_Sort_Array
{
    class FindBiggestElementAndSortArray
    {
        static void Main(string[] args)
        {
            int[] array = new int[] { 9, 8, 5, 20, 13, 7, 6, 18, 11, 19, 1, 3, 12, 2, 16, 15, 4, 10, 14, 17 };
            Console.Write("Enter the starting position (0 - 19): ");
            string input = Console.ReadLine();
            int startPosition;

            if (int.TryParse(input, out startPosition))
            {
                startPosition = int.Parse(input);

                if (startPosition < 0 || startPosition > 19)
                {
                    Console.WriteLine("Position out of range.");
                    return;
                }
            }
            else
            {
                Console.WriteLine("Invalid input.");
                return;
            }

            Console.Write("Enter the ending position (0 - 19): ");
            input = Console.ReadLine();
            int endPosition;

            if (int.TryParse(input, out endPosition))
            {
                endPosition = int.Parse(input);

                if (startPosition < 0 || endPosition > 19)
                {
                    Console.WriteLine("Position out of range.");
                    return;
                }
            }
            else
            {
                Console.WriteLine("Invalid input.");
                return;
            }

            if (endPosition < startPosition)
            {
                int swap = endPosition;
                endPosition = startPosition;
                startPosition = swap;
            }

            Console.Write("Choos sorting order. Enter 1 for intcreesing." + 
                        "enter 2 for decreasing. ");
            input = Console.ReadLine();
            int order;

            if (int.Parse(input) == 1 || int.Parse(input) == 2)
            {
                order = int.Parse(input);
            }
            else
            {
                Console.WriteLine("Invalid input.");
                return;
            }

            int biggestElement = FindBiggestElement(array, startPosition, endPosition);
            Console.WriteLine("The biggest element in range {0} - {1} is {2}",
                            startPosition, endPosition, biggestElement);

            PrintArray(order == 1 ? SortIncreasingArray(array) : SortDecreasingArray(array));
        }

        private static int FindBiggestElement(int[] arr, int start, int end)
        {
            int element = arr[start];

            for (int i = start; i < end; i++)
            {
                element = Math.Max(element, arr[i]);
            }

            return element;
        }

        private static int[] SortDecreasingArray(int[] array)
        {
            for (int i = 0; i < array.Length - 1; i++)
            {
                for (int j = i + 1; j < array.Length; j++)
                {
                    if (array[i] < array[j])
                    {
                        int swap = array[i];
                        array[i] = array[j];
                        array[j] = swap;
                    }
                }
            }

            return array;
        }

        private static int[] SortIncreasingArray(int[] array)
        {
            for (int i = 0; i < array.Length - 1; i++)
            {
                for (int j = i + 1; j < array.Length; j++)
                {
                    if (array[i] > array[j])
                    {
                        int swap = array[i];
                        array[i] = array[j];
                        array[j] = swap;
                    }
                }
            }

            return array;
        }

        private static void PrintArray(int[] arr)
        {
            for (int i = 0; i < arr.Length; i++)
            {
                Console.Write(arr[i]);

                if (i < arr.Length - 1)
                {
                    Console.Write(", ");
                }
            }

            Console.WriteLine();
        }        
    }
}

Task-10-N Factorial From 1 To 100

using System;
using System.IO;
using System.Numerics;

namespace Task_10_N_Factorial_From_1_To_100
{
    class FactorialFromOneToHundred
    {
        static void Main(string[] args)
        {
            Stream buffer = Console.OpenStandardInput(1000);
            Console.SetIn(new StreamReader(buffer, Console.InputEncoding, false, 1000));

            string input = Console.ReadLine();
            BigInteger number;

            if (BigInteger.TryParse(input, out number))
            {
                number = BigInteger.Parse(input);
            }
            else
            {
                Console.WriteLine("Invalid input.");
                return;
            }

            PrintFactorial(number);
        }

        private static void PrintFactorial(BigInteger number)
        {
            for (int i = 1; i < 100; i++)
            {
                number *= i;
                Console.WriteLine("Factorial n{0} is {1}", i, number);
            }
        }
    }
}

Task-11-Few Tasks

using System;
using System.Linq;

namespace Task_11_Few_Tasks
{
    class FewTasks
    {
        static void Main(string[] args)
        {
            System.Threading.Thread.CurrentThread.CurrentCulture =
                System.Globalization.CultureInfo.InvariantCulture;

            Console.WriteLine("Choose an operation.");
            Console.WriteLine("Press 1 to reverse number.");
            Console.WriteLine("Press 2 to calculate the average of given sequence");
            Console.WriteLine("Press 3 to solve the linear equation a * x + b = 0");
            string input = Console.ReadLine();
            int optionNumber;

            if (int.TryParse(input, out optionNumber))
            {
                if (int.Parse(input) == 1 || int.Parse(input) == 2 || int.Parse(input) == 3)
                {
                    optionNumber = int.Parse(input);
                }
                else
                {
                    Console.WriteLine("Invalid input.");
                    return;
                }
            }
            else
            {
                Console.WriteLine("Invalid input.");
                return;
            }

            if (optionNumber == 1)
            {
                PrintReversedNumber();
            }
            else if (optionNumber == 2)
            {
                GetAverageValue();
            }
            else if (optionNumber == 3)
            {
                SolveLinearEquation();
            }
        }

        private static void SolveLinearEquation()
        {
            Console.Write("Enter number a (a != 0): ");
            string input = Console.ReadLine();
            double numberA;

            if (double.TryParse(input, out numberA))
            {
                numberA = double.Parse(input);
            }
            else
            {
                Console.WriteLine("Invalid input.");
                return;
            }

            if (numberA == 0)
            {
                Console.WriteLine("Number a must not be 0.");
                return;
            }

            Console.Write("Enter number b: ");
            input = Console.ReadLine();
            double numberB;

            if (double.TryParse(input, out numberB))
            {
                numberB = double.Parse(input);
            }
            else
            {
                Console.WriteLine("Invalid input.");
                return;
            }

            double numberX = (numberB * -1) / numberA;
            Console.WriteLine("Number x is : {0:F3}", numberX);
        }

        private static void GetAverageValue()
        {
            Console.WriteLine("Enter a sequence of numbers separate by single space.");

            try
            {
                double[] sequence = Console
                .ReadLine()
                .Split(new Char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)
                .Select(item => double.Parse(item))
                .ToArray();

                double sum = 0.0;

                foreach (var num in sequence)
                {
                    sum += num;
                }

                Console.WriteLine("The avarage value of the sequence is: {0:F5}",
                    sum / sequence.Length);
            }
            catch
            {
                Console.WriteLine("Invalid sequence input.");
                return;
            }
        }

        private static void PrintReversedNumber()
        {
            Console.WriteLine("Enter a number to reverse.");
            string input = Console.ReadLine();
            int number;

            if (int.TryParse(input, out number))
            {
                number = int.Parse(input);
            }
            else
            {
                Console.WriteLine("Invalid input.");
                return;
            }

            int reversedNumber = RverseNumber(number);
            Console.WriteLine("The reversed number is: {0}", reversedNumber);
        }

        private static int RverseNumber(int number)
        {
            int reversedNumber = 0;

            while (number > 0)
            {
                reversedNumber += number % 10;
                reversedNumber *= 10;
                number /= 10;
            }

            reversedNumber /= 10;
            return reversedNumber;
        }
    }
}

Task-12-Calculate Polynom

using System;
using System.Linq;

namespace Task_12_Calculate_Polynom
{
    class CalculatePolynom
    {
        static void Main(string[] args)
        {
            try
            {
                Console.WriteLine("Enter first polynom's coefficients starting by the lowest,\n" +
                    "separate by space (only numbers). Enter 0 to miss a power.");
                int[] firstPolynom = GetPolynom();

                Console.WriteLine("Enter second polynom's coefficients starting by the lowest,\n" +
                    "separate by space (only numbers). Enter 0 to miss a power.");
                int[] secondPolynom = GetPolynom();

                int[] resultPolynom = new int[firstPolynom.Length + secondPolynom.Length + 1];
                resultPolynom = AddPolynoms(resultPolynom, firstPolynom, secondPolynom);
                PrintPolynom(firstPolynom);
                Console.WriteLine(" + ");
                PrintPolynom(secondPolynom);
                Console.WriteLine(" == ");
                PrintPolynom(resultPolynom);
            }
            catch
            {
                Console.WriteLine("ERROR!");
                return;
            }
        }

        private static int[] GetPolynom()
        {
            int[] polynom = Console
            .ReadLine()
            .Split(new Char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)
            .Select(item => int.Parse(item))
            .ToArray();

            return polynom;
        }

        private static void PrintPolynom(int[] polynom)
        {
            for (int i = polynom.Length - 1; i > -1; i--)
            {
                if (polynom[i] != 0)
                {
                    Console.Write(polynom[i] < 0 ? "-" : "");
                    break;
                }
            }

            for (int i = polynom.Length - 1; i > 0; i--)
            {
                if (polynom[i] != 0)
                {
                    Console.Write("{0}x^{1} {2} ", Math.Abs(polynom[i]), i,
                    polynom[i - 1] != 0 ? polynom[i - 1] < 0 ? " - " : " + " : "");
                }
            }

            if (polynom[0] != 0)
            {
                Console.WriteLine(Math.Abs(polynom[0]));
            }
            else
            {
                Console.WriteLine();
            }
        }

        private static int[] AddPolynoms(int[] result, int[] polynom1, int[] polynom2)
        {
            for (int i = 0; i < result.Length; i++)
            {
                int num1 = i < polynom1.Length ? polynom1[i] : 0;
                int num2 = i < polynom2.Length ? polynom2[i] : 0;
                result[i] = num1 + num2;
            }

            return result;
        }
    }
}

Task-13-Multiply Polynoms

using System;
using System.Linq;

namespace Task_13_Multiply_Polynoms
{
    class MultiplyPolynoms
    {
        static void Main(string[] args)
        {
            try
            {
                Console.WriteLine("Enter first polynom's coefficients starting by the lowest,\n" +
                    "separate by space (only numbers). Enter 0 to miss a power.");
                int[] firstPolynom = GetPolynom();

                Console.WriteLine("Enter second polynom's coefficients starting by the lowest,\n" +
                    "separate by space (only numbers). Enter 0 to miss a power.");
                int[] secondPolynom = GetPolynom();

                int[] resultPolynom = new int[firstPolynom.Length + secondPolynom.Length + 1];
                resultPolynom = MultiPolynoms(resultPolynom, firstPolynom, secondPolynom);
                PrintPolynom(firstPolynom);
                Console.WriteLine(" * ");
                PrintPolynom(secondPolynom);
                Console.WriteLine(" == ");
                PrintPolynom(resultPolynom);
            }
            catch
            {
                Console.WriteLine("Invalid input.");
                return;
            }
        }

        private static int[] GetPolynom()
        {
            int[] polynom = Console
            .ReadLine()
            .Split(new Char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)
            .Select(item => int.Parse(item))
            .ToArray();

            return polynom;
        }        

        private static void PrintPolynom(int[] polynom)
        {
            for (int i = polynom.Length - 1; i > -1; i--)
            {
                if (polynom[i] != 0)
                {
                    Console.Write(polynom[i] < 0 ? "-" : "");
                    break;
                }
            }
           
            for (int i = polynom.Length - 1; i > 0; i--)
            {
                if (polynom[i] != 0)
                {
                    Console.Write("{0}x^{1} {2} ", Math.Abs(polynom[i]), i,
                    polynom[i - 1] != 0 ? polynom[i - 1] < 0 ? " - " : " + " : "");
                }
            }

            if (polynom[0] != 0)
            {
                Console.WriteLine(Math.Abs(polynom[0]));
            }
            else
            {
                Console.WriteLine();
            }
        }

        private static int[] MultiPolynoms(int[] result, int[] polynom1, int[] polynom2)
        {
            for (int p1 = 0; p1 < polynom1.Length; p1++)
            {
                for (int p2 = 0; p2 < polynom2.Length; p2++)
                {
                    result[p1 + p2] += polynom1[p1] * polynom2[p2];
                }
            }

            return result;
        }
    }
}