# Average of a stream of numbers

• Difficulty Level : Easy
• Last Updated : 17 Jun, 2022

Difficulty Level: Rookie

Given a stream of numbers, print the average (or mean) of the stream at every point. For example, let us consider the stream as 10, 20, 30, 40, 50, 60, …

```  Average of 1 numbers is 10.00
Average of 2 numbers is 15.00
Average of 3 numbers is 20.00
Average of 4 numbers is 25.00
Average of 5 numbers is 30.00
Average of 6 numbers is 35.00
..................```
Recommended Practice

To print the mean of a stream, we need to find out how to find the average when a new number is being added to the stream. To do this, all we need is the count of numbers seen so far in the stream, previous average, and new number. Let n be the count, prev_avg be the previous average and x be the new number being added. The average after including x number can be written as (prev_avg*n + x)/(n+1).

Output :

```Average of 1 numbers is 10.000000
Average of 2 numbers is 15.000000
Average of 3 numbers is 20.000000
Average of 4 numbers is 25.000000
Average of 5 numbers is 30.000000
Average of 6 numbers is 35.000000 ```

Time Complexity: O(n)

Auxiliary Space: O(1)

The above function getAvg() can be optimized using the following changes. We can avoid the use of prev_avg and the number of elements by using static variables (Assuming that only this function is called for an average of stream). Following is the optimized version.

## C++

 `#include ``using` `namespace` `std;` `// Returns the new average after including x``float` `getAvg(``int` `x)``{``    ``static` `int` `sum, n;` `    ``sum += x;``    ``return` `(((``float``)sum) / ++n);``}` `// Prints average of a stream of numbers``void` `streamAvg(``float` `arr[], ``int` `n)``{``    ``float` `avg = 0;``    ``for` `(``int` `i = 0; i < n; i++)``    ``{``        ``avg = getAvg(arr[i]);``        ``cout<<``"Average of "``<

## C

 `#include ` `// Returns the new average after including x``float` `getAvg(``int` `x)``{``    ``static` `int` `sum, n;` `    ``sum += x;``    ``return` `(((``float``)sum) / ++n);``}` `// Prints average of a stream of numbers``void` `streamAvg(``float` `arr[], ``int` `n)``{``    ``float` `avg = 0;``    ``for` `(``int` `i = 0; i < n; i++) {``        ``avg = getAvg(arr[i]);``        ``printf``(``"Average of %d numbers is %f \n"``, i + 1, avg);``    ``}``    ``return``;``}` `// Driver program to test above functions``int` `main()``{``    ``float` `arr[] = { 10, 20, 30, 40, 50, 60 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);``    ``streamAvg(arr, n);` `    ``return` `0;``}`

## Java

 `// Java program to return``// Average of a stream of numbers``class` `GFG``{``static` `int` `sum, n;``    ` `// Returns the new average``// after including x``static` `float` `getAvg(``int` `x)``{``    ``sum += x;``    ``return` `(((``float``)sum) / ++n);``}` `// Prints average of a``// stream of numbers``static` `void` `streamAvg(``float``[] arr,``                      ``int` `n)``{``    ``float` `avg = ``0``;``    ``for` `(``int` `i = ``0``; i < n; i++)``    ``{``        ``avg = getAvg((``int``)arr[i]);``        ``System.out.println(``"Average of "``+ (i + ``1``) +``                           ``" numbers is "` `+ avg);``    ``}``    ``return``;``}` `// Driver Code``public` `static` `void` `main(String[] args)``{``    ``float``[] arr = ``new` `float``[]{ ``10``, ``20``, ``30``,``                               ``40``, ``50``, ``60` `};``    ``int` `n = arr.length;``    ``streamAvg(arr, n);``}``}` `// This code is contributed by mits`

## Python3

 `# Returns the new average``# after including x``def` `getAvg(x, n, ``sum``):``    ``sum` `=` `sum` `+` `x;``    ``return` `float``(``sum``) ``/` `n;` `# Prints average of a``# stream of numbers``def` `streamAvg(arr, n):``    ``avg ``=` `0``;``    ``sum` `=` `0``;``    ``for` `i ``in` `range``(n):``        ``avg ``=` `getAvg(arr[i], i ``+` `1``, ``sum``);``        ``sum` `=` `avg ``*` `(i ``+` `1``);``        ``print``(``"Average of "``, end ``=` `"");``        ``print``(i ``+` `1``, end ``=` `"");``        ``print``(``" numbers is "``, end ``=` `"");``        ``print``(avg);``    ``return``;` `# Driver Code``arr``=` `[ ``10``, ``20``, ``30``,``       ``40``, ``50``, ``60` `];``n ``=` `len``(arr);``streamAvg(arr,n);` `# This code is contributed by mits`

## C#

 `using` `System;` `class` `GFG``{``static` `int` `sum, n;``    ` `// Returns the new average``// after including x``static` `float` `getAvg(``int` `x)``{` `    ``sum += x;``    ``return` `(((``float``)sum) / ++n);``}` `// Prints average of a``// stream of numbers``static` `void` `streamAvg(``float``[] arr, ``int` `n)``{``    ``float` `avg = 0;``    ``for` `(``int` `i = 0; i < n; i++)``    ``{``        ``avg = getAvg((``int``)arr[i]);``        ``Console.WriteLine(``"Average of {0} numbers "` `+``                             ``"is {1}"``, (i + 1), avg);``    ``}``    ``return``;``}` `// Driver Code``static` `int` `Main()``{``    ``float``[] arr = ``new` `float``[]{ 10, 20, 30,``                               ``40, 50, 60 };``    ``int` `n = arr.Length;``    ``streamAvg(arr, n);` `    ``return` `0;``}``}` `// This code is contributed by mits`

## PHP

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## Javascript

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Output:

```Average of 1 numbers is 10.0
Average of 2 numbers is 15.0
Average of 3 numbers is 20.0
Average of 4 numbers is 25.0
Average of 5 numbers is 30.0
Average of 6 numbers is 35.0```

Time Complexity: O(n)

Auxiliary Space: O(1)

Thanks to Abhijeet Deshpande for suggesting this optimized version.

Related article:
Program for an average of an array (Iterative and Recursive)

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