# How to find index of a given element in a Vector in C++

Given a vector V consisting of N integers and an element K, the task is to find the index of element K in the vector V. If the element does not exist in vector then print -1.

Examples:

Input: V = {1, 45, 54, 71, 76, 17}, K = 54
Output: 2
Explaination :
The index of 54 is 2, hence output is 2.

Input: V = {3, 7, 9, 11, 13}, K = 12
Output: -1

Approach:
Follow the steps below to solve the problem:

• Index of an element in a vector can be found with the help of the two predefined functions in stl:

• find(): Used to find the position of element in the vector.
• distance(): Used to find distance between base iterater of vector and iterator return by find() function.
1. Finaly return the distance returned by distance() function.

Below is the implementation of the above approach :

## C++

 `// C++ program to find the index ` `// of an element in a vector ` ` `  `#include ` `using` `namespace` `std; ` ` `  `// Function to print the ` `// index of an element ` `void` `getIndex(vector<``int``> v, ``int` `K) ` `{ ` `    ``auto` `it = find(v.begin(), ` `                   ``v.end(), K); ` ` `  `    ``// If element was found ` `    ``if` `(it != v.end()) { ` `        ``// calculating the index ` `        ``// of K ` `        ``int` `index = distance(v.begin(), ` `                             ``it); ` `        ``cout << index << endl; ` `    ``} ` `    ``else` `{ ` `        ``// If the element is not ` `        ``// present in the vector ` `        ``cout << ``"-1"` `<< endl; ` `    ``} ` `} ` `// Driver Code ` `int` `main() ` `{ ` `    ``// Vector ` `    ``vector<``int``> v = { 1, 45, 54, 71, ` `                      ``76, 17 }; ` `    ``// Value whose index ` `    ``// needs to be found ` `    ``int` `K = 54; ` `    ``getIndex(v, K); ` `    ``return` `0; ` `} `

Output:

```2
```

Time Complexity : O (N)
Auxiliary Space : O (1)

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