IndexOf ExamplesΒΆ

The general syntax for this method is:

stringName.IndexOf(substr);

Given a candidate substring, this method returns the integer index of the first occurrence of the substring in the string. If the substring does not occur in the string, -1 is returned.

Example

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Console.WriteLine("LaunchCode".IndexOf('C'));

Console.WriteLine("LaunchCode".IndexOf('A'));

Console.WriteLine("dogs and dogs and dogs!".IndexOf("dog"));

Output

6
-1
0

Example

An email address must contain an @ symbol. Checking for the presence of this symbol is a part of email address verification in most programs.

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string input = "[email protected]";
int atIndex = input.IndexOf('@');

if (atIndex > -1) {
   Console.WriteLine("Email contains @");
} else {
   Console.WriteLine("Invalid email");
}

Output

Email contains @