#include <stdio.h>

int readData(double data[], int size)	/* Change return type */
{
    FILE* fp;
    fp = stdin; /* fopen("data.txt", "r"); temporary change to check */
    int i;

    for (i = 0; i < size; i++)
    {
        if( fscanf(fp, "%lf", &data[i]) < 1) break; /* Added */
        if(data[i] < 0)
            printf("Negative data at %d\n", i);
    }
    size = i;

    printf("The array is: ");
    for (i = 0; i < size; i++)
    {
        printf("%f ", data[i]);
    }
    /* fclose(fp); temporary */
    printf("\n");

    return size;
}

int main(void) {
	double arr[100];
	size_t size = readData(arr, 100);
	printf("Size of array = %u\n", size);
	return 0;
}