C# program to find the index of a word in a string

Finding the index of a word in a string or array is a common programming task in C#. The Array.IndexOf() method provides an efficient way to locate the position of a specific element within an array of strings.

Syntax

Following is the syntax for using Array.IndexOf() method −

int index = Array.IndexOf(array, searchValue);

Parameters

• array − The one-dimensional array to search
• searchValue − The object to locate in the array

Return Value

The method returns the index of the first occurrence of the specified value. If the value is not found, it returns -1.

Using Array.IndexOf() to Find Word Index

Declare and initialize an array −

string[] str = new string[] {
   "Cat",
   "Mat", 
   "Rat"
};

Now, use IndexOf() method to find the index of the word "Mat" −

Array.IndexOf(str, "Mat");

Example

using System;

public class Demo {
   public static void Main() {
      string[] str = new string[] {
         "Cat",
         "Mat",
         "Rat"
      };
      Console.WriteLine("Our Array =");
      for (int i = 0; i < str.Length; i++) {
         string res = str[i];
         Console.WriteLine(res);
      }
      int findIndex = Array.IndexOf(str, "Mat");
      Console.Write("Element Mat found at the following index: ");
      Console.WriteLine(findIndex);
   }
}

The output of the above code is −

Our Array =
Cat
Mat
Rat
Element Mat found at the following index: 1

Finding Index in a String Using String.IndexOf()

For finding a word within a single string, use the String.IndexOf() method −

Example

using System;

public class StringIndexDemo {
   public static void Main() {
      string sentence = "The quick brown fox jumps over the lazy dog";
      string searchWord = "brown";
      
      int index = sentence.IndexOf(searchWord);
      
      if (index != -1) {
         Console.WriteLine("Word '{0}' found at index: {1}", searchWord, index);
      } else {
         Console.WriteLine("Word '{0}' not found", searchWord);
      }
   }
}

The output of the above code is −

Word 'brown' found at index: 10

Handling Case When Word Is Not Found

Example

using System;

public class IndexNotFoundDemo {
   public static void Main() {
      string[] animals = {"Dog", "Cat", "Bird", "Fish"};
      string searchAnimal = "Lion";
      
      int index = Array.IndexOf(animals, searchAnimal);
      
      if (index == -1) {
         Console.WriteLine("'{0}' not found in the array", searchAnimal);
      } else {
         Console.WriteLine("'{0}' found at index: {1}", searchAnimal, index);
      }
   }
}

The output of the above code is −

'Lion' not found in the array

Conclusion

The Array.IndexOf() method efficiently finds the index of a word in a string array, returning -1 if not found. For searching within a single string, use String.IndexOf(). Always check for -1 to handle cases where the search term is not present.