The **```strings```** **package** is a Go standard library package that contains functions to manipulate UTF-8 encoded strings.

#   
#  ```Index()``` method

It provides the **```Index()``` method**, which returns the index of the first occurrence of the input substring in the input string.

#   
#  Syntax
```
func Index(s, substr string) int
```
##  
## Arguments
This method takes a string ```s``` and another string ```substr``` to search as inputs.

##  
## Return value
- This method returns the index of the first occurrence of the substring ```substr``` in the input string ```s```.

- It returns **-1** if ```substr``` does not exist in ```s```.

#   
## Code 
First, we imported the ```fmt``` and ```strings``` package to our program in the code below:

package main

import (
	"fmt"
	"strings"
)

func main() {
	str1 := "educative.io"
	fmt.Println("String : ", str1)
	index1 :=  strings.Index(str1, "io")
	index2 :=  strings.Index(str1, "shots")
	fmt.Println("substring : io,", "Index : ", index1)
	fmt.Println("substring : shots,", "Index : ", index2)
}

#   
#  Explanation
- After importing ```fmt```, we call the ```Index()``` method with ```"educative.io"``` as the input string and ```"io"``` as the substring to search and get the index. This returns **```10```**, as ```"io"``` is present at index **```10```** in the input string ```"eductive.io"```.

- We again call the ```Index()``` method with ```"educative.io"``` as the input string and ```"shots"``` as the substring to search and get the index. This returns **```-1```**, as ```"shots"``` is not present in the input string ```"eductive.io"```.

- We show the output of all these operations using the ```Println()``` method of the ```fmt``` package.
##  
## Output
The program shows the below output and exits:

```
String :  educative.io
substring : io, Index :  10
substring : shots, Index :  -1
```

What is the Index() function in Go?

`Index()` method

Syntax

Arguments

Return value

Code

Explanation

Output