finding the sum of array class

[cash]

I'm confused on how I can find the sum of the array

  DollarAmount sum(DollarAmount a[], int size){ // calculates the sum of the Array of dollars
    DollarAmount s;
    for(int x=0; x<size; x++){
        s=s+a[x];
    }
    return(s);
}

[George P]

DollarAmount s = 0; or C++11 DollarAmount s { };

s += a[x];