C Program to Find Sum of Array Elements

To find the sum of array elements in C, use a loop to add each element to a sum variable like for(int i = 0; i < n; i++) sum += arr[i];.

Examples

Inputarr = {1, 2, 3, 4, 5}, n = 5

OutputSum of array elements: 15

Inputarr = {10, 20, 30}, n = 3

OutputSum of array elements: 60

Inputarr = {}, n = 0

OutputSum of array elements: 0

How to Think About It

To find the sum, think of adding each number in the list one by one. Start with zero, then add the first number, then the second, and so on until all numbers are added. The final total is the sum.

Algorithm

1

Get the number of elements in the array.

2

Initialize a variable sum to zero.

3

Loop through each element in the array.

4

Add the current element to sum.

5

After the loop ends, return or print the sum.

Code

c

#include <stdio.h>

int main() {
    int arr[] = {1, 2, 3, 4, 5};
    int n = 5;
    int sum = 0;

    for (int i = 0; i < n; i++) {
        sum += arr[i];
    }

    printf("Sum of array elements: %d\n", sum);
    return 0;
}

Output

Sum of array elements: 15

Dry Run

Let's trace the array {1, 2, 3, 4, 5} through the code

1

Initialize sum

sum = 0

2

Add first element

sum = 0 + 1 = 1

3

Add second element

sum = 1 + 2 = 3

4

Add third element

sum = 3 + 3 = 6

5

Add fourth element

sum = 6 + 4 = 10

6

Add fifth element

sum = 10 + 5 = 15

Iteration	Current Element	Sum After Addition
1	1	1
2	2	3
3	3	6
4	4	10
5	5	15

Why This Works

Step 1: Initialize sum to zero

We start with sum = 0 because we have not added any elements yet.

Step 2: Loop through each element

The for loop goes through each element in the array one by one.

Step 3: Add each element to sum

Inside the loop, we add the current element to sum using sum += arr[i].

Step 4: Print the final sum

After the loop ends, sum holds the total, which we print using printf.

Alternative Approaches

Using while loop

c

#include <stdio.h>

int main() {
    int arr[] = {1, 2, 3, 4, 5};
    int n = 5, i = 0, sum = 0;
    while (i < n) {
        sum += arr[i];
        i++;
    }
    printf("Sum of array elements: %d\n", sum);
    return 0;
}

This uses a while loop instead of for loop; functionally the same but slightly different syntax.

Using recursion

c

#include <stdio.h>

int sumArray(int arr[], int n) {
    if (n <= 0) return 0;
    return arr[n-1] + sumArray(arr, n-1);
}

int main() {
    int arr[] = {1, 2, 3, 4, 5};
    int n = 5;
    printf("Sum of array elements: %d\n", sumArray(arr, n));
    return 0;
}

This uses recursion to add elements; elegant but uses more memory due to function calls.

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

Time Complexity

The program loops through all n elements once, so time grows linearly with input size.

Space Complexity

Only a few variables are used regardless of input size, so space is constant.

Which Approach is Fastest?

The iterative for loop is fastest and simplest; recursion adds overhead and uses more memory.

Approach	Time	Space	Best For
For loop	O(n)	O(1)	Simple and efficient for all array sizes
While loop	O(n)	O(1)	Same as for loop, just different syntax
Recursion	O(n)	O(n)	Good for learning recursion but less efficient