passing array to function in c - c

Question

can someone please help me figure out what i'm doing wrong here? i'm getting inaccurate results here. I seem to be getting the first value in the array each time and i cant seem to figure out what i'm doing incorrectly
#include <stdio.h>
int getbillsum ( int price[] );
int main( void )
{
int itemprice [10];
int total = 0;
for (int c=0;c <10;c++ ) //Looping to get item prices
{
printf ("\nEnter the price of the item: ");
scanf (" %d", &itemprice[c]);
}
total = getbillsum (itemprice);
printf ("%d", total);
return 0;
}
int getbillsum (int price []) //function to sum the values in array
{
int sum = 0;
for (int i=0; i<sizeof(price); i++)
{
sum+=price[i];
}
return sum;
}

Answer 1

You can't pass arrays to functions in C (well, not as an array anyway). Arrays decay into pointers, the sizeof which is always the same (4 for 32 bit systems, 8 for 64 bits).
For more information see paragraph 2.3 here.
The easiest, most common and most reliable way of solving your issue is to pass the length of the array as a second argument:
int getbillsum (int *price, size_t len)
{
int sum = 0;
for (int i=0; i<len; ++i)
sum += price[i];
return sum;
}
//usage
int main ( void )
{
int price[10];
for(int i=0;i<10;++i)
scanf(" %d", &price[i]);
printf("Sum: %d\n", getbillsum(price, sizeof(price)/sizeof(*price)));
return 0;
}
You also had a problem in your code: you added the return statement inside of your loop.
Just a quick-tip: The sum of an array of ints is not unlikely to be too much for a single int to hold, so I'd change the return-type of getbillsum to long, too
I've also edited your question, addressing quite a lot of issues considering how short your code was:
int getbillsum ( price );//missing type, changed to
int getbillsum ( int price[] );//better would be int getbillsum ( int *price ); but considering your question, left it as array
scanf ("%d", &itemprice[c]);//unsafe, changed it to
scanf (" %d", &itemprice[c]);//add space
total = getbillsum (itemprice,9);//why the second param?
total = getbillsum (itemprice);//to match function prototype
return sum;//moved OUTSIDE of the loop...

Answer 2

sizeof(price) does not give you the length of the array, but the size of the pointer (int price[]), which is probably 4. Also, you immediately return in the first for run. Put return outside the for loop.
You do fix it by supplying the array size, but you never use it. Update your getbillsum function:
int getbillsum (int price [], int length) //function to sum the values in array
{
int sum = 0;
for (int i=0; i<length; i++)
{
sum+=price[i];
}
return sum;
}

Answer 3

In addition to posted answers, you can consider a technique suggested in this answer.
Edit Quoted from comment
it's non-standard, dangerous (think of overflow, forgetting to
dereference at the correct offset and the like), and you should not
try this
In your case it will be something like that :
void *p = calloc(sizeof(itemprice) + sizeof(unsigned long int),1));
*((unsigned long int*)p) = 10;
quote from linked answer
n is now stored at ((unsigned long int)p)
Your getbillsum will look like that now (did not compile it, consider it as pseudocode)
int getbillsum (void* p)
{
int* price = p+sizeof(unsigned long int);
unsigned long int size = *p;
int sum = 0;
for (int i=0; i<size; i++)
{
sum+=price[i];
}
return sum;
}