Coding Challenge 3

Suppose that you need to create a collection of variables of the same type that's why you need an array. Arrays help you to store multiple values in a single variable. In my recent post, i shared with you decision making, while, doWhile. In this section, we will learn about arrays after learning for loop and for each loop.

For Loop

A for loop is similar to while loop but there is a difference. To use a for loop, you need to execute a specific number of times.

Exercise 1

for (int i = 0; i < 10; i++)
{
    Console.WriteLine($"Num: {i}");
}

When you run this code, you will see the numbers from one to ten on the console in order.

Exercise 2

Write all the even numbers from one to an other number entered by an user.

int num = Convert.ToInt32(Console.ReadLine());
for (int i = 0; i < num; i++)
{
    if (i%2 ==0)
    {
        Console.WriteLine(i);
    }
}

Infinite for loop

 for (; ; )
{
    Console.WriteLine("This is an infitine loop.");

}

Exercise 1

In this code, we get inputs from the user until he/she press "q".Then, we sum the negative numbers and positive numbers separately.

int negSum = 0;
int posSum = 0;
for (; ;)
{
    Console.WriteLine("Enter a number");
    string value = Console.ReadLine();
    if (value.ToLower()=="q")
    {
        Console.WriteLine("negatif:" + negSum);
        Console.WriteLine("positive:" + posSum);
        break;
    }else if(value == "34" || value == "-34")
    {
        Console.WriteLine("You entered an unvalid number");
        continue;
    }
    else
    {
        int intNum = Convert.ToInt32(value);
        if (intNum < 0)
        {
            negSum += intNum;

        }
        else if (intNum > 0)
        {
            posSum += intNum;

        }
    }
}

Foreach Loop

Let's you to loop through elements in an array. In the next section, you will see how to use it.

foreach (var item in collection)
	{

	}

Arrays

What does array mean? Let's discover it together! An array is just a collection of elements of the same type.

// type[] arr = new type[10]
// type[] arr = {element1,element2,element3}

To create an array with 10 ints

int[] numberArray = new int[10];
int[] numbersArray = {1,2,3,4,5,6,7,8,9}; // This is an other way to do the same thing but there is not any number in the numbers array because we didn't added any int into it.

To create an array of strings

string[] strArray = new string[10];
string[] strArray = {"1asd","2asd","3asd","4asd","5asd","6asd","7asd","8asd","9asd"};

To create an array of doubles

double[] doubleArray = new double[10];
double[] doubleArray = {1,2,3,4,5,6,7,8,9};

To access an elements

int[] numbersArray = {1,2,3,4,5,6,7,8,9}; 
Console.WriteLine(numbersArray[3])

To create an array of different type objects

object[] mixedArray = new object[10]; 
mixedArray[0] = 5;
mixedArray[2] = "string";
mixedArray[3]= 14.5f;
Console.WriteLine(mixedArray[2]);

In the code below, i tried to print all elements of numbersArray.

int[] numbersArray = {1,2,3,4,5,6,7,8,9}; 
for (int i = 0; i < 10; i++)
{
    Console.WriteLine(numbersArray[i])
}

Exercise 1

Write the code that ask a user to enter names, push them into array and print

string[] names = new string[10];
for (int i = 0; i < 10; i++)
{
    string name = Console.ReadLine();
    names[i] = name;

}

for (int i = 0; i < names.Length; i++)
{
    Console.WriteLine(names[i]);
}

Exercise 2

Generating 10 numbers randomly, adding them into array and printing all the elements of this array.

int[] arr = new int[10];
Random randomNum;
for (int i = 0; i < 10; i++)
{
    randomNum = new Random();
    arr[i] =  randomNum.Next(0,100);
}
foreach (var item in arr)
{
    Console.WriteLine(item);
}

It’s possible to know how many times an element is repeated in the array.

Exercise 3

int[] numbers = { 10, 20, 30, 40, 10, 14, 10, 20, 30 };
int count10 =puanlar.Count(sayi=> sayi == 10)
Console.WriteLine($"{count10} is repeated 10 times in the array 10");

If you want to learn the index of this repeatitions, you can use Array.indexOf()

Exercise 4

int[] numbers = { 10, 20, 30, 40, 10, 14, 10, 20, 30 };
int count10 =puanlar.Count(sayi=> sayi == 10)
int startİndex = 0;

for (int i = 0; i < count10; i++)
{
    startIndex = Array.IndexOf(numbers, 10, startIndex);
    Console.WriteLine($"The index of {count10}");
    startIndex += 1;
}

when Array.indexOf() couldn’t find the element in the array, it returns -1

How to Copy an array and copy one part of an array?

int[] arr1 = { 11, 20, 45, 55, 66, 48, 20, 30, 40};
int[] arr2  =  new int[9];
arr1.CopyTo(arr2,0);

// Array.Copy() starts copying 5 items from 3td elements into arr2 at index 0 
Array.Copy(arr1, 3, arr2, 0, 5);

Multidimensional Arrays

Let’s create two dimensional array which contains 5 row and 5 columns.

int[,] matrix = new int[5, 5];
marrix[0,0] = 10 // Addin 10 at (0,0)
marrix[0,0] = 100 // Addin 100 at (1,0)
marrix[0,0] = 12 // Addin 12 at (0,1)

Exercise 5

2 0 0 0 2
1 0 0 0 1
2 0 0 0 2
1 0 0 0 1
2 0 0 0 2

for (int i = 0; i < 5; i++)
{
    for (int j = 0; j < 5; j++)
    {
        if (i % 2 == 0 &&(j==0 || j==4))
        {
            matris2[i, j] = 2;
           
        }
        else if (i % 2 == 1 && (j == 0 || j == 4))
        {
            matris2[i, j] = 1;
        }
    }
}

for (int i = 0; i < 5; i++)
{
    for (int j = 0; j < 5; j++)
    {
        Console.Write(matris2[i, j]+" ");
       }
       Console.Write("\n");
}