C Program to Find Average of Array Elements

To find the average of an array in C, sum all elements using a loop and then divide by the number of elements, like average = sum / (float)size;.

Examples

InputArray: [5, 10, 15]

OutputAverage: 10.00

InputArray: [1, 2, 3, 4, 5]

OutputAverage: 3.00

InputArray: [0, 0, 0, 0]

OutputAverage: 0.00

How to Think About It

To find the average, first add all numbers in the array to get the total sum. Then, divide this sum by how many numbers are in the array. This gives the average value.

Algorithm

1

Get the size of the array.

2

Initialize a variable to store the sum as 0.

3

Loop through each element of the array and add it to the sum.

4

Divide the sum by the size of the array to get the average.

5

Print or return the average.

Code

c

#include <stdio.h>

int main() {
    int arr[] = {1, 2, 3, 4, 5};
    int size = sizeof(arr) / sizeof(arr[0]);
    int sum = 0;
    for (int i = 0; i < size; i++) {
        sum += arr[i];
    }
    float average = sum / (float)size;
    printf("Average: %.2f\n", average);
    return 0;
}

Output

Average: 3.00

Dry Run

Let's trace the array [1, 2, 3, 4, 5] through the code to find the average.

1

Initialize sum and size

sum = 0, size = 5

2

Add elements to sum

sum = 1 + 2 + 3 + 4 + 5 = 15

3

Calculate average

average = 15 / 5 = 3.0

4

Print average

Output: Average: 3.00

Iteration	Element	Sum after addition
1	1	1
2	2	3
3	3	6
4	4	10
5	5	15

Why This Works

Step 1: Summing elements

We add each element of the array using a loop to get the total sum.

Step 2: Calculating average

We divide the total sum by the number of elements using sum / (float)size to get a float result.

Step 3: Printing result

We print the average with two decimal places using printf("%.2f").

Alternative Approaches

Using a function to calculate average

c

#include <stdio.h>

float findAverage(int arr[], int size) {
    int sum = 0;
    for (int i = 0; i < size; i++) {
        sum += arr[i];
    }
    return sum / (float)size;
}

int main() {
    int arr[] = {10, 20, 30};
    int size = sizeof(arr) / sizeof(arr[0]);
    float avg = findAverage(arr, size);
    printf("Average: %.2f\n", avg);
    return 0;
}

This approach improves code reuse by separating logic into a function.

Using floating-point array for more precise sum

c

#include <stdio.h>

int main() {
    float arr[] = {1.5, 2.5, 3.5};
    int size = sizeof(arr) / sizeof(arr[0]);
    float sum = 0.0f;
    for (int i = 0; i < size; i++) {
        sum += arr[i];
    }
    float average = sum / size;
    printf("Average: %.2f\n", average);
    return 0;
}

This method handles decimal numbers directly for more accurate averages.

Complexity: O(n) time, O(1) space

Time Complexity

The program loops through all n elements once to sum them, so time complexity is O(n).

Space Complexity

Only a few variables are used regardless of input size, so space complexity is O(1).

Which Approach is Fastest?

All approaches have similar O(n) time; using a function adds clarity but no speed difference.

Approach	Time	Space	Best For
Simple loop in main	O(n)	O(1)	Quick scripts or learning
Function for average	O(n)	O(1)	Reusable code and clarity
Floating-point array	O(n)	O(1)	Handling decimal values accurately