Pointers and arrays without using index - c

Question

I have been asked to sum up an int array and return the sum not using index.
(function needs to get the array and the size)
I know I should've set a pointer to the array and compare the pointer to the array address and use pointer++ to run over the array.
Tho, I wrote down the following code :
int sumArray(int nNumArray[], int nSize)
{
int nSum = 0;
while(*nNumArray <= &nNumArray[nSize-1])
{
nSum += *nNumArray;
nNumArray++;
}
return nSum;
}
which works perfectly,
thing is *nNumArray is referring to values and &nNumArray[nSize-1] is referring to an address.
I'm trying to understand how come this way works.
Will appreciate some insights. Thanks.

Answer 1

The while loop condition is incorrect:
while(*nNumArray <= &nNumArray[nSize-1])
because you are comparing an integer (*nNumArray) with a pointer (&nNumArray[nSize-1]). Compiler must be giving warning message on this statement.
Instead, you can do:
int sumArray(int nNumArray[], int nSize)
{
int nSum = 0;
while(nSize--)
{
nSum += *nNumArray;
nNumArray++;
}
return nSum;
}

Answer 2

"which works perfectly" : this is impossible
(*nNumArray <= &nNumArray[nSize-1]) : you compare an int into the vector (and later outside it) and an address of an int into the vector ( and in fact after its end). A priori your compiler signal the error
Furthermore &nNumArray[nSize-1] will not be the end of the vector after the first loop because you modify nNumArray
If you want to use a pointer you can use an other variable to store it to not modify nNumArray, and to change test like (ptr <= &nNumArray[nSize-1]) :
#include <stdio.h>
int sumArray(int nNumArray[], int nSize)
{
int nSum = 0;
int * ptr = nNumArray;
while(ptr <= &nNumArray[nSize-1])
{
nSum += *ptr++;
}
return nSum;
}
int main()
{
int a[3] = {1,2,3};
printf("%d\n", sumArray(a, 3));
return 0;
}

Answer 3

First error here :
(*nNumArray <= &nNumArray[nSize-1])
The name of the array variable itself is considered as a pointer in C, thus *nNumArray represents the reference of an pointer.
It should be nNumArray to make it compare the address.
Second error :
It won't work perfectly if only the first error is fixed.
The index operation works like this :
&nNumArray[nSize-1] works the same as nNumArray + nSize - 1
Thus the while loop might looks like this :
while(nNumArray <= nNumArray + nSize - 1){
nSum += *nNumArray;
nNumArray++;
}
(This might makes it more simple to see where is wrong)
The while loop will run forever until *nNumArray accessed an int which is out of the array that causes a segmentation fault.
You might want to do it by using another pointer to compare with nNumArray + nSize - 1, and the whole sumArray function should look like this:
int sumArray(int nNumArray[], int nSize)
{
int nSum = 0;
int *ptr = nNumArray;
while(ptr <= nNumArray + nSize - 1)
{
nSum += *ptr;
ptr++;
}
return nSum;
}
And now it should work perfectly :)