Question

I’m workingon a way to average arbitrarily many numbers in Objective-C, and this is my method so far:

-(double)average:(double)num, ...
{
    va_list args;
    va_start(args, num);

    double currentAverage = num;
    long long timesAveraged = 1;
    for(double d in args)
        currentAverage = ((currentAverage * timesAveraged) + d) / ++timesAveraged;//Error occurs on this line
    return currentAverage;

}

However, when I compile it, I get an error stating that “Selector element does not have a valid object type“, so my first solution was to change the method to the following:

-(double)average:(double)num, ...
{
    va_list args;
    va_start(args, num);

    double currentAverage = num;
    long long timesAveraged = 1;
    for(NSNumber *d in args)
        currentAverage = ((currentAverage * timesAveraged) + [d doubleValue]) / ++timesAveraged;//Error occurs on this line
    return currentAverage;

}

However, now it gives me the unsettlingly similar error that “Expression does not have a valid object type“.

I’m obviously doing this wrong. Any suggestions on how to do this right?

Solution

---

I’ve been able to compile the file by writing the method as such:

-(double)average:(double)num, ...
{
    va_list args;
    va_start(args, num);

    double currentAverage = num;
    long long timesAveraged = 1;
    for (NSNumber *arg = [NSNumber numberWithDouble:num]; arg != nil; arg = va_arg(args, NSNumber*))
    {
        currentAverage = ((currentAverage * timesAveraged) + [arg doubleValue]) / ++timesAveraged;
    }
    va_end(args);
    return currentAverage;

}

Answer 1

As trudyscousin mentioned fast enumeration won’t work here. You should also use va_arg to extract data from the arguments list. Read more about it here: http://cocoawithlove.com/2009/05/variable-argument-lists-in-cocoa.html