C# IndexOf

In C#, the IndexOf method is used to find the index of the first occurrence of a specified substring or character within a string.

Syntax

The syntax for using IndexOf in C# is as follows:

public int IndexOf(string substring)
public int IndexOf(string substring, int startIndex)
public int IndexOf(char value)
public int IndexOf(char value, int startIndex)

• substring - The substring to search for
• startIndex - The index to start searching from (optional)
• value - The character to search for

Return Value

The IndexOf method returns the zero-based index of the first occurrence of the specified substring or character within the calling string. If the substring or character is not found, it returns -1.

Examples

Example 1: Find IndexOf a Substring

string str = "Hello World";
int index = str.IndexOf("World"); // Returns 6

Example 2: Find IndexOf a Character

string str = "Hello World";
int index = str.IndexOf('o'); // Returns 4

Example 3: Find IndexOf a Substring with a Start Index

string str = "Hello World";
int index = str.IndexOf("o", 5); // Returns 7

Example 4: Check if Substring Exists

string str = "Hello World";
bool exists = str.IndexOf("foo") != -1; // Returns false

Conclusion

In conclusion, IndexOf is a useful method for finding the index of the first occurrence of a specified substring or character within a string in C#. It can be used in a variety of ways and is a great addition to any C# programmer's arsenal.