Array Average in C++

Calculate average of array elements in C++.

BeginnerArray ProgramsExample 2 of 4

array-average.cpp

1#include <iostream>
2#include <iomanip>
3using namespace std;
4
5int main() {
6    int n;
7    double sum = 0;
8    
9    cout << "Enter number of elements: ";
10    cin >> n;
11    
12    int arr[n];
13    
14    cout << "Enter " << n << " elements: ";
15    for (int i = 0; i < n; i++) {
16        cin >> arr[i];
17        sum += arr[i];
18    }
19    
20    double average = sum / n;
21    
22    cout << fixed << setprecision(2);
23    cout << "Average of array elements: " << average << endl;
24    
25    return 0;
26}

Output

Enter number of elements: 5
Enter 5 elements: 10 20 30 40 50
Average of array elements: 30.00

What's going on

What is an Array Average?

The average of an array is the sum of all elements divided by the number of elements.

Formula:

1Average = (Element1 + Element2 + ... + ElementN) / N

Example:

If array = [10, 20, 30, 40, 50]

Sum = 10 + 20 + 30 + 40 + 50 = 150

Number of elements = 5

Average = 150 / 5 = 30.00

Header Files

The program uses two header files:

`#include <iostream>`

Provides cout for output and cin for input

`#include <iomanip>`

Provides fixed and setprecision() for formatting decimal output

Ensures the average is displayed with exactly 2 decimal places

Variable Declarations

1int n;
2double sum = 0;
3int arr[n];
4double average;

Explanation:

`n`

: Stores the number of elements in the array (integer)

`sum`

: Accumulates the sum of all array elements (initialized to 0)

Uses double to handle decimal results accurately

`arr[n]`

: The array to store the elements

Size is determined by user input n

`average`

: Stores the calculated average (double for decimal precision)

Why `double` for sum and average?

Even if array elements are integers, the average might be a decimal

Example: Average of [1, 2, 3] = 2.00 (decimal result)

Using double ensures accurate decimal calculations

Taking Input: Number of Elements

cout << "Enter number of elements: ";

cin >> n;

The program first asks the user how many elements they want to enter. This determines the size of the array.

Example:

If user enters 5, then n = 5, and the array will have 5 elements.

Declaring the Array

int arr[n];

This creates an array of size n to store the elements.

Note:

Variable-length arrays (VLAs) like this work in some C++ compilers, but the standard approach is to use vectors or dynamic allocation. However, for beginners, this syntax is simpler to understand.

Taking Input: Array Elements

1for (int i = 0; i < n; i++) {
2cin >> arr[i];
3sum += arr[i];
4}

1cout << "Enter " << n << " elements: ";

Step-by-step:

1.The program asks the user to enter n elements

2.A loop runs from i = 0 to i < n (0-indexed)

3.For each iteration:

cin >> arr[i]; reads one element and stores it in the array

sum += arr[i]; adds the element to the running sum

Example with n = 5:

User enters: 10 20 30 40 50

Iteration 1: arr[0] = 10, sum = 0 + 10 = 10

Iteration 2: arr[1] = 20, sum = 10 + 20 = 30

Iteration 3: arr[2] = 30, sum = 30 + 30 = 60

Iteration 4: arr[3] = 40, sum = 60 + 40 = 100

Iteration 5: arr[4] = 50, sum = 100 + 50 = 150

Key Technique: Accumulation

sum += arr[i]; is equivalent to sum = sum + arr[i];

This accumulates (adds up) all values as we read them

By the end of the loop, sum contains the total of all elements

Calculating the Average

double average = sum / n;

This line calculates the average by dividing the sum by the number of elements.

Important:

Since both sum and average are double, the division will be floating-point division, giving a decimal result.

Example:

sum = 150 (as double: 150.0)

n = 5

average = 150.0 / 5 = 30.0

Formatting the Output

1cout << fixed << setprecision(2);
2cout << "Average of array elements: " << average << endl;

`fixed`

Ensures numbers are displayed in fixed-point notation (not scientific notation)

Example: 30.00 instead of 3e+01

`setprecision(2)`

Sets the number of decimal places to 2

Example: 30.0 becomes 30.00, 25.5 stays 25.50

Why format the output?

Makes the result look professional and consistent

Important for financial, scientific, and statistical applications

Users expect a certain number of decimal places

Complete Program Flow

1.Ask user for number of elements (n)

2.Declare array of size n

3.Initialize sum = 0

4.Loop through array:

Read each element

Add to sum

5.Calculate average = sum / n

6.Format output to 2 decimal places

7.Display the average

Key Concepts Demonstrated

Array Input

: Reading multiple values into an array using a loop

Accumulation Pattern

: Using sum += arr[i] to accumulate values is a common pattern in programming

Type Conversion

: Using double ensures decimal division even when dividing integers

Output Formatting

: Using fixed and setprecision() for professional-looking output

Array Traversal

: Iterating through all elements of an array using a for loop

Common Variations

Variation 1: Calculate average separately (two loops)

1for (int i = 0; i < n; i++) {
2cin >> arr[i];
3}
4
5// Second loop: Calculate sum
6for (int i = 0; i < n; i++) {
7sum += arr[i];
8}

1// First loop: Read elements

Variation 2: Using float instead of double

1float sum = 0, average;

1// ... rest of code

Variation 3: Finding average of specific range

1for (int i = 0; i < 3; i++) {
2sum += arr[i];
3}
4average = sum / 3;

1// Average of first 3 elements only

Common Mistakes

Not initializing sum

: Forgetting sum = 0 gives incorrect results

Integer division

: Using int for sum/average loses decimal precision

Wrong loop bounds

: Using i <= n instead of i < n (array out of bounds)

Dividing by zero

: If n = 0, division by zero causes error

Not formatting output

: Missing fixed << setprecision(2) gives inconsistent decimal places

Practical Applications

Array averages are used in:

Statistics

: Calculating mean values

Data Analysis

: Analyzing datasets

Grading Systems

: Calculating student averages

Performance Metrics

: Average scores, times, etc.

Financial Calculations

: Average prices, returns, etc.

Scientific Computing

: Average measurements, readings

Edge Cases to Consider

Empty array

: n = 0 → Division by zero error

Negative numbers

: Works fine, but average might be negative

Very large numbers

: May cause overflow if using int for sum

Very small numbers

: Precision issues with floating-point

Improved version with error checking:

1if (n <= 0) {
2}

1cout << "Error: Number of elements must be positive!" << endl;
2return 1;

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