二进制表达式的操作数无效，C

Question

Im working on a function that takes some values and finds the min, max, and average of the values. I'm passing everything to the function by reference and am getting some errors when I try and do basic operations like + and / Namely the error is

Invalid operands to binary expression ('double *' and 'double *')

void MinMaxAvg(double *pA, double *min, double *max, double *avg, int lines, double *total )
{
    for (int i=0; i<lines; i++)
    {
        if ( i==0)
        {
            min = &pA[0];
            max = &pA[0];
        }
        else
        {
            if (&pA[i] < min)
            {
                min = &pA[i];
            }

            if (&pA[i] > max)
            {
                max = &pA[i];
            }
        }

        total += &pA[i];     //<-- Errors on this line

    }

    avg = (total / lines);         // <-- Errors on this line.

}

Answer 1

It seems like you're getting some of the types confused there. In your example you're setting the pointers to a new value, not the value of said pointers.

The first would have to be:

*total += pA[i];

While the second should be:

*avg = (*total / lines);

In fact, you probably want to use floating point division on the second error there (some compilers are notorious for using integer divison in unexpected places):

*avg = (*total / (double)lines);

You'll still be getting errors if you do it like that, however. For example &pA[i] > ... will result in a pointer comparison, ie the address of the pointers will be compared. Most likely not what you want.

Answer 2

You're trying to add an address to a pointer, that's not a valid operation.

You probably meant:

*total += pA[i];

Your use of &pA seems very confused, as does the re-assignment of the pointers min and max .

If you have a pointer to a value (like double *min ), then *min is how you access (read or write) the value being pointed at.

Answer 3

There is no "pass by reference" in C language unlike C++. You should dereference each pointer in your code if you want work with variables values. Now you work with variables addresses.