Iterate through int array of unknown length - c

Question

I am trying to iterate through an array that will contain up to a maximum of 4 elements - no other knowledge of the array-length exists.
Pseudo Code
void insert_vals(uint8_t num, uint8_t *match_num, uint8_t *value)
{
uint8_t i;
while(data_exists) // how do I determine if data exists in 'value'?
{
switch(num)
{
case 0:
{
switch(match_num[i])
{
case 0:
hw0reg0 = value[i];
case 1:
hw0reg1 = value[i];
case 2:
hw0reg2 = value[i];
case 3:
hw0reg3 = value[i];
}
}
case 1:
{
switch(match_num[i])
{
case 0:
hw1reg0 = value[i];
case 1:
hw1reg1 = value[i];
case 2:
hw1reg2 = value[i];
case 3:
hw1reg3 = value[i];
}
}
// etc. 2 other cases
}
i++;
}
}
Calling Example (Pseudo Code)
/*
* num: hardware device select from 1 - 4
* match_num: 4 possible matches for each hardware device
* value: 32-bit values to be assigned to 4 possible matches
* NOTE: This function assumes hardware devices are selected
* in a consecutive order; I will change this later.
*/
// example calling code - we could have configured 4 hardware devices
insert_vals(0, [0, 1], [0x00000001, 0x000000FF]); // arg2 and arg3 equal in length
How can I accomplish this?
In a character array, C will automatically add '\0' to the end of the array, but this does not seem to be the case for an integer array. If I was somehow able to determine the length of match_num and value (see if statement) at runtime originally, then that would allow me to create a for loop.
Edit
Since I know that there will be a maximum of 4 elements, couldn't I do something similar to the following?
void insert_vals(uint8_t num, uint8_t *match_num, uint32_t *value)
{
int i;
for(i = 0; i < 4; i++)
{
if(value[i] == -1)
break;
else
{
// Assign data
}
}
}

Answer 1

You can't get the length of an array pointed to given only the pointer. Either you have to pass the length, or it must be constant (always 4) with some sentinel value in the unused elements -- a value that is somehow invalid for your computations (like NUL is for strings).

Answer 2

Is there a value you can guarantee it's not in the "usable" data? (e.g. 0 is no valid character for character strings, therefore Mr. Kernighan and Mr. Ritchie decided to pick it as a "end of array" marker. You could do the same with any value.
Say you know your integer values are between 0 to 512, so you could initialize the whole array e.g. to 1024, then fill it and iterate through it until a number >512 occurs (which has to be your end of array marker).
Another possibility is to pass the number of elements in the array along with the array.