Looping through Arrays

It is very useful to be able to quickly go through all the elements of an array and perform some operation on them or extract their values.

There are a number of ways we can do that however the most common is using the for and foreach loops.

In the case of using the for loop, we can use the loop's i variable for indexing:

main


              12345678910111213141516
            
using System;

namespace ConsoleApp
{
    internal class Program
    {
        static void Main(string[] args)
        {
			int[] numbers = { 5, 10, 15, 20, 25 };

			for(int i = 0; i < 5; i++) {
			    Console.WriteLine(numbers[i]);
			}
        }
    }
}

In the above code we wrote the condition i < 5 where we chose 5 as the limit. Instead of manually counting the number of elements we can also use the Length attribute of the arrays to access the length (size) of an array:

main


              12345678910111213
            
using System;

namespace ConsoleApp
{
    internal class Program
    {
        static void Main(string[] args)
        {
			int[] myArray = new int[10];
			Console.WriteLine(myArray.Length); // Output: 10
        }
    }
}

Using the length attribute the loop will look something like this:

main


              12345678910111213141516
            
using System;

namespace ConsoleApp
{
    internal class Program
    {
        static void Main(string[] args)
        {
			int[] numbers = { 5, 10, 15, 20, 25 };

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

We can also output the numbers in reverse by modifying the loop to run in the opposite direction:

main


              1234567891011121314151617
            
using System;

namespace ConsoleApp
{
    internal class Program
    {
        static void Main(string[] args)
        {
			int[] numbers = { 5, 10, 15, 20, 25 };

			for (int i = numbers.Length - 1; i >= 0; i--)
			{
    			Console.WriteLine(numbers[i]);
			}
        }
    }
}

We initiate i with the value numbers.Length - 1, because the index of the last element of an array is 1 less than the size of that array, so in this case the loop variable will start from value 9. The loop condition i >= 0 ensures that the loop continues till i reaches 0. We decrement the value of i every iteration.

Another slightly easier method of looping through arrays is by using the foreach loop. The syntax of a foreach loop is as follows:

main


              1234
            
foreach (datatype variableName in arrayName) 
{
    // code block to be executed
}

For-example:

main


              12345678910111213141516
            
using System;

namespace ConsoleApp
{
    internal class Program
    {
        static void Main(string[] args)
        {
			int[] numbers = { 5, 10, 15, 20, 25 };

			foreach(int n in numbers) {
    			Console.WriteLine($"Number: {n}");
			};
        }
    }
}

The foreach loop is simpler than the for loop however the difference is that we cannot modify the original elements of the array in a foreach loop. If we try to assign a new value to n in the above code, the compiler will show an error. However, it is possible in the for loop, since we know the indices of the elements we can modify the array:

main


              1234567891011121314151617181920
            
using System;

namespace ConsoleApp
{
    internal class Program
    {
        static void Main(string[] args)
        {
			int[] numbers = { 5, 10, 15, 20, 25 };

			for(int i = 0; i < numbers.Length; i++) {
    			numbers[i] *= 2;
			};

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

Everything was clear?

Section 5. Chapter 7