sum array element to form a given sum code example

Example 1: Write a program to find the sum of all sub-arrays of a given integer array.

long int SubArraySum( int arr[] , int n ) 
{ 
    long int result = 0; 
  
    // computing sum of subarray using formula 
    for (int i=0; i<n; i++) 
        result += (arr[i] * (i+1) * (n-i)); 
  
    // return all subarray sum 
    return result ; 
}

Example 2: sum of an array

const sum = (...args) => args.reduce((a, b) => a + b, 0);
console.log(sum(1,2,3)); // returns 6