"Array subscript is not an integer" in C program

Question

The deviation function throws me the following error: "Array subscript is not an integer". If you can help me locate the cause of error I'll appreciate it.

float average(float data[], int n) {
    float total = 0;
    float *p = data;

    while (p < (data + n)) {
        total = total + *p;
        p++;
    }

    return total / n;
}

float deviation(float data[], int n) {
    float data_average = average(data, n);
    float total;
    float *p = data;

    while (p < (data + n)) {
        total += (data[p] - data_average) * (data[p + 1] - data_average);
    }

    return total / 2;
}

Answer 1

p is a pointer to a float. That's why you're getting the error.

float *p, total;

...

total += (datos[p]-prom)*(datos[p+1]-prom);

You can only use ints as array indices in C.

Answer 2

Array subscripts must be an integer, an int type. You can't use any other type as array subscript. p is declared as float *p, i.e, a pointer to float. You can't use a pointer as array indices.