C :: Check Number Of Elements In Array

I can have at most 3 structs in array, but it could be 0,1,2 or 3 structs in array. I am trying to avoid dynamic memory allocation. I initialize sensors to 3 to reserve space for them in memory, since there may be at most 3 elements in the array. But I am testing a condition where there will only be 2 elements:

Code:

#include <stdio.h>#include <stdlib.h>
#include <string.h>
typedef struct {
unsigned long long int address;
float current;
unsigned char pressure_units;
} sensor;

[Code]...

The problem is even though there are only 2 sensors out of 3 in the array, sizeof(sensors)/sizeof(sensors[0]) returns 3. I assume because when it allocates memory for 3, it includes that allocated memory even though it really doesn't contain the struct. How can I figure out how many elements were really inserted into array, not just allocated to array?