C Program to Find the Sum of Elements of an Array

Given an array of integers, find the sum of its elements.

Examples:

Input : arr[] = {1, 2, 3}
Output : 6
Explanation: 1 + 2 + 3 = 6

Input : arr[] = {15, 12, 13, 10}
Output : 50

C

/* C Program to find sum of elements
 in a given array */
#include <bits/stdc++.h>

// function to return sum of elements
// in an array of size n
int sum(int arr[], int n)
{
    int sum = 0; // initialize sum

    // Iterate through all elements
    // and add them to sum
    for (int i = 0; i < n; i++)
        sum += arr[i];

    return sum;
}

int main()
{
    int arr[] = { 12, 3, 4, 15 };
    int n = sizeof(arr) / sizeof(arr[0]);
    printf("Sum of given array is %d", sum(arr, n));
    return 0;
}

Output

Sum of given array is 34

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

Another Method#2: Using Recursion

C

/* C++ Program to find sum of elements
in a given array using recursion */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// function to return sum of elements
// in an array of size n
int sum(int arr[], int n)
{
    // base case
    if (n == 0) {
        return 0;
    }
    else {
        // recursively calling the function
        return arr[0] + sum(arr + 1, n - 1);
    }
}

int main()
{
    int arr[] = { 12, 3, 4, 15 };
    int n = sizeof(arr) / sizeof(arr[0]);

    printf("%d", sum(arr, n));

    return 0;
}

Output

34

Time Complexity: O(n)
Auxiliary Space: O(n)

Another Method#3: Using prefix sum

C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
    int vec[] = { 12, 3, 4, 15 };
    int n = sizeof(vec) / sizeof(vec[0]);

    // storing all the prefix here
    int prefix[n];
    // pushing the first element of the vec array
    // into the prefix array
    prefix[0] = vec[0];

    for (int i = 1; i < n; i++) {
        // calculating the further prefix sum
        int temp = prefix[i - 1] + vec[i];
        prefix[i] = temp;
    }

    // last element of the prefix array
    // will the sum of all elements of the
    // vec array
    printf("%d\n", prefix[n - 1]);

    return 0;
}

Output

34

Time Complexity: O(n)
Auxiliary Space: O(n), for recursive stack space.