Finding whether a number exists as sum of two array elements in an unsorted array

Given the array{2, 10,9,7,8 ,-2}

Find whether sum 8 is possible

As element no.2 (10) and element no.6(-2) are present the sum of the two is 8

Solution: Taking an Sum minus the fixed element, we scan through rest of the array to find another element matching

Complexity: O(n^2)

#include <stdio.h>

int main()

{

    int a[6] = {2, 10,9,7,8 ,-2};

    

    int sum = 8;

    

    int flag = 0;

    int size = sizeof a / sizeof a[0];

    printf("\nSize of array %d", size);

    int i=0;

    int j =0;

    for (i= 0; i<size-1; i++) {

        for(j=i+1; j <size;j++) {

            if(sum-a[i] == a[j]) {

                flag++;

                break;

            }

        }

        if(flag==1) {

            break;

        }

    }

    

    if(flag) {

     printf("\n Element at location(%d):%d and location(%d):%d has sum:%d", i+1,a[i],j+1,a[j],sum);

    }

    else {

        printf("Not found !!");

    }

    return 0;

}

Output:

Size of array 6                                                                                                               

 Element at location(2):10 and location(6):-2 has sum:8