Lære Substring Extraction & Indexing | Fundamentals of Strings

When working with strings in C#, you often need to extract specific parts of a larger text—such as pulling out a first name from a full name, or finding a particular word in a sentence. To do this, you must understand zero-based indexing, which means that the first character in a string is at position 0, the second at position 1, and so on. Extracting substrings involves specifying the position (index) where you want to start, and sometimes how many characters to include.

Program.cs


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using System;

namespace ConsoleApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            string fullName = "John Doe";
            int spaceIndex = fullName.IndexOf(' ');
            string firstName = fullName.Substring(0, spaceIndex);
            string lastName = fullName.Substring(spaceIndex + 1);

            Console.WriteLine("First name: " + firstName);
            Console.WriteLine("Last name: " + lastName);
        }
    }
}

In this example, you see how IndexOf is used to find the position of the first space character in the string, which separates the first and last names. The Substring method then extracts the first name by starting at index 0 and taking all characters up to the space, and the last name by starting right after the space and taking the rest of the string. IndexOf returns the index of the first occurrence of the specified character, while Substring can extract text starting from a given index, and optionally for a specified length.

Program.cs


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using System;

namespace ConsoleApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            string input = "SingleName";
            int spaceIndex = input.IndexOf(' ');

            if (spaceIndex != -1)
            {
                string firstPart = input.Substring(0, spaceIndex);
                string secondPart = input.Substring(spaceIndex + 1);
                Console.WriteLine("First part: " + firstPart);
                Console.WriteLine("Second part: " + secondPart);
            }
            else
            {
                Console.WriteLine("No space found in input.");
            }
        }
    }
}

It is important to handle cases where the character you are searching for is not present in the string. IndexOf returns -1 if the character cannot be found, so you should always check for this before using the result with Substring. This prevents errors and allows you to handle edge cases, such as when a delimiter is missing, in a user-friendly way.

Definition

Definition: Zero-based indexing means that counting starts from 0. In string manipulation, the first character is at index 0, the second at index 1, and so on. This is essential for correctly specifying positions when extracting or searching within strings.


              123
            
string text = "Example";
int position = text.IndexOf('a'); // Finds the index of 'a'
string part = text.Substring(2, 3); // Extracts 3 characters starting at index 2

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Sektion 1. Kapitel 3

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Suggested prompts:

Can you explain how to handle cases where the character isn't found in the string?

What happens if I use Substring with an invalid index?

Can you give more examples of extracting parts of a string in C#?

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Program.cs


              12345678910111213141516171819
            
using System;

namespace ConsoleApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            string fullName = "John Doe";
            int spaceIndex = fullName.IndexOf(' ');
            string firstName = fullName.Substring(0, spaceIndex);
            string lastName = fullName.Substring(spaceIndex + 1);

            Console.WriteLine("First name: " + firstName);
            Console.WriteLine("Last name: " + lastName);
        }
    }
}

Program.cs


              1234567891011121314151617181920212223242526
            
using System;

namespace ConsoleApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            string input = "SingleName";
            int spaceIndex = input.IndexOf(' ');

            if (spaceIndex != -1)
            {
                string firstPart = input.Substring(0, spaceIndex);
                string secondPart = input.Substring(spaceIndex + 1);
                Console.WriteLine("First part: " + firstPart);
                Console.WriteLine("Second part: " + secondPart);
            }
            else
            {
                Console.WriteLine("No space found in input.");
            }
        }
    }
}

Definition


              123
            
string text = "Example";
int position = text.IndexOf('a'); // Finds the index of 'a'
string part = text.Substring(2, 3); // Extracts 3 characters starting at index 2

Var alt klart?

Tak for dine kommentarer!

Sektion 1. Kapitel 3

Substring Extraction & Indexing

1. What does IndexOf(' ') return for the string "John Doe"?

2. Which method extracts a portion of a string?

3. If IndexOf returns -1, what does it mean?

Substring Extraction & Indexing

1. What does IndexOf(' ') return for the string "John Doe"?

2. Which method extracts a portion of a string?

3. If IndexOf returns -1, what does it mean?