Question

Hey there,
I have a probably straight-forward question about the following problem:

I have a function

double afunction(double *myarray)
{   
    double ret = 1.0;
    for(int i = 0; i < 4; i++)
        ret *= myarray[i]*myarray[i];
    return ret;
}

Now I want to modify it so that I pass two new parameters: int index describing which index of myarray to change like the following: myarray[ index ] = *add;. This would be the following:

double afunction(double *myarray, int index, double *add)
{   
    myarray[ index ] += *add;
    double ret = 1.0;
    for(int i = 0; i < 4; i++)
        ret *= myarray[i]*myarray[i];
    return ret;
}

The problem is: I don’t want to modify the array myrray and I don’t want to create a new array for this because of memory-regards (this will later be computed on the GPU and there I couldn’t allocate a whole new array in a kernel function anyway.
Easy solution to this?
Thanks!

EDIT
Sorry, I mistyped something. Instead myarray[ index ] = *add; I meant to say myarray[ index ] += *add;

EDIT2
Example of a bigger function which could later on easily be extended to about 50 different return-cases. So to have the if-statement to modify the certain value myarray[index] with adding *add in each return-case is pretty ugly 🙁

double afunction(double *myarray, int funcIndex, int indexAdd, double *add)
{   
    myarray[ indexAdd ] += *add;

    if(funcIndex >= 1 && funcIndex <= 4)
        return myarray[1]*myarray[1]*myarray[2];

    switch(funcIndex)
    {
        case 5:
            return sin(myarray[3]) * cos(myarray[1]);
        case 6:
            double ret = exp(myarray[1]);
            for(int i = 1; i < 5; i++)
                ret *= (myarray[ i ]-myarray[ 5-i ]);
            return ret;
        case 7:
            double ret = 0.0;
            for(int i = 1; i < 10; i++)
                ret += myarray[ i ];
            return ret;
    }

    return 0.0;
}

Answer 1

double afunction(double *myarray, int index, double *add)
{   
    double ret = (*add) * (*add);
    for(int i = 0; i < 4; i++)
        if( i != index )
            ret *= myarray[i]*myarray[i];
    return ret;
}