calculate the sum of all element in a double array

Question

i am a bit confused in using array in doing recursion, can anyone correct my mistake?

new update, based on question required some of the line cannot be edit

double sum_of_array(double x[],int size)
{


    static double sum; <---can be edit

    int index = 0; <--can be edit

    if(index<size){

        return sum + sum_of_array(x,size-1); <--can be edit

    }

    else {
       something ; <--can be edit
       return sum; <--can be edit

    }
}

int main(void){

    double x[] = {4.5,5.0,6.8};

    double y[] = {4.7,3.4,2.5,5.2};

    cout<<"Sum X = "<<sum_of_array(x,3)<<endl;

    cout<<"Sum Y = "<<sum_of_array(y,4)<<endl;

    return 0;
}

output:

Sum of the element in X[]=15.3

Sum of the element in Y[]= 15.8

Answer 1

The logic of your recursive function is just wrong. You never actually read the contents of the array. I'm surprised you got any meaningful output out of that.

You need to rethink of the recursive definition to perform this addition.

Base case(s):
Sum of an empty array is 0..
i.e., sum_of_array(x, 0) == 0.

Sum of a 1-element array is the value of the element.
i.e., sum_of_array(x, 1) == x[0]

Recursive case:
Sum of an n-element array is the sum of the nth element and the sum of the first n-1 elements.
i.e., sum_of_array(x, n) == x[n-1] + sum_of_array(x, n-1)

Figure out how to encode this logic in your function.

Answer 2

Ok last attempt:

double sum_of_array(double x[], int index, int size)
{
    if(index < size){
        return x[index] + sum_of_array(x, index + 1, size);
    }
    else {
        return 0;
    }

}

then

cout<<"Sum X = "<<sum_of_array(x,0,3)<<endl;

Answer 3

I hope I can still chime in with my answer. The most recent answer excluding mine is from 2011.

This is yet another solution to calculate the sum of all elements in an array.

double array_sum(double *p_array, int idx_low, int idx_high){
   if(idx_low == idx_high)
      return p_array[idx_low];
   int idx_mid=idx_low+(idx_high-idx_low)/2;
   return array_sum(p_array,idx_low,idx_mid)+array_sum(idx_mid+1, idx_high);
}

Analysis of this algorithm would yeild a run-time of O(n*log(n)). However, you'd do wise to take this statement with a pinch of salt.

Answer 4

Error is you did not initialized static variable sum.

Answer 5

There are quite some errors in this code:

• First, the constant sum seems to be useless. What is ever used for?
• Second, you never take the contents of x in your function.

Answer 6

Ok then it should be like this:

double sum_of_array(double x[],int index)
{
    int size = sizeof( x) / sizeof( x[0] );
    if(index<size){
        return x[index] + sum_of_array(x, index + 1);
    }
    return 0;

}

then call

sum_of_array(x,0);

IE you always call the first time with 0 as the index