Find a character in a string in C#

1. string.IndexOf(): Returns the index of the first occurrence of a character.
2. string.LastIndexOf(): Returns the index of the last occurrence of a character.
3. string.Contains(char): Checks if a character exists in the string.

Let’s explore each method with examples.

Using string.IndexOf() to Find a Character

string.IndexOf() returns the index of the first occurrence of a character in the string, searching from left to right. If the character is not found, it returns -1.

var input = "programming is fun";

var index = input.IndexOf('g');

if (index > -1)
{
    Console.WriteLine($"Found 'g' at index {index}");
}

In this example, the character 'g' appears twice, and it returns the index of the first occurrence:

Output:

Found 'g' at index 3

Case-Insensitive Search with IndexOf()

To perform a case-insensitive search with IndexOf(), use the StringComparison overload.

var input = "CSharp Programming";

int index = input.IndexOf('p', StringComparison.CurrentCultureIgnoreCase);

if (index > -1)
{
    Console.WriteLine($"Found 'p' at index {index}");
}

This example returns the index of 'P' despite the character being uppercase in the string.

Output:

Found 'p' at index 8

Using string.LastIndexOf() to Find a Character

string.LastIndexOf() returns the index of the last occurrence of a character in a string, searching from right to left. If the character is not found, it returns -1.

var input = "openAI is amazing";

var index = input.LastIndexOf('i');

if (index > -1)
{
    Console.WriteLine($"Found 'i' at index {index}");
}

In this case, the last occurrence of 'i' is returned:

Output:

Found 'i' at index 12

Case-Insensitive Search with LastIndexOf()

To perform a case-insensitive search with LastIndexOf(), use the StringComparison overload. You need to pass the character as a string when using StringComparison.

var input = "Hello Universe";

char findChar = 'h';

var index = input.LastIndexOf(findChar.ToString(), StringComparison.CurrentCultureIgnoreCase);

if (index > -1)
{
    Console.WriteLine($"Found 'h' at index {index}");
}

This example searches for 'h' case-insensitively.

Output:

Found 'h' at index 0

Using string.Contains() to Check if a Character Exists

If you simply want to know whether a character exists in the string, use string.Contains(char).

var input = "searching for a letter";

if (input.Contains('r'))
{
    Console.WriteLine("Found 'r'");
}

This will check if 'r' exists in the string.

Output:

Found 'r'

Case-Insensitive Search with Contains()

To search case-insensitively with string.Contains(), you can use the StringComparison overload.

var input = "EXAMPLE Text";

if (input.Contains('e', StringComparison.InvariantCultureIgnoreCase))
{
    Console.WriteLine("Found 'e'");
}

This performs a case-insensitive check for 'e'.

Output:

Found 'e'

These are a few ways to find a character in a string in C#. The choice of method depends on whether you need the index of the character, the position of the last occurrence, or just a simple existence check.