Passing an array to a function and subset sum program - c

Question

I'm trying to create a programm to find all subsets whose elements sum to a specific target. My logic is : Let's say I have an array of 6 elements like this one
{3,2,4,1,1,9}.
To find a subset whose elements sum to the number 5, all I have to is get the first element and if its value is smaller than 5 then I move to the next elements of the array and I look for subsets whose elements sum to the difference : 5-value of the first element and so on.
Of course if the value of the element is greater than 5 then I move to the next element.
I've been trying to do this with a recursive function in which I will pass my array.
My problem is that I can't understand how to pass my array into my function and how am I supposed to move to the next element using my function again. To be my honest I did my research on this topic and I couldn't really find anything that helped me.
I use C and I declare my function like this void subset(int x[],int n); where n is the number of the elements of my array. I can't really understand the x[] part. My brother told me to do it like this but I can't really understand why.

Answer 1

So you're trying to pass your array into a function? An array has elements or members which will be referenced using the brackets "[ ]" for example in the array "int arry[6]={1,2,3,6,5};" the first element would be the number "1" which we can access using arry[0]
With all due respect it seems like you did not do your "honest research" in this area and I suggest you continue as arrays are an integral part of almost every language.
Below is some c code which should help you get started on your homework. int arry[] is a completely different type than lets say "int arry". The bracket part tells us that it is an array.
#include <stdio.h>
int main()
{
int arry[6]={1,2,3,6,5};
myFunction(arry,4);
return 0;
}
int myFunction(int myarr[], int x){
printf("the number %d element is %d",x+1,myarr[4]);
return 0;
}

Answer 2

Here's an elaborate solution. For the given data, it produces:
Data (6): 3 2 4 1 1 9
Found: 3 + 2 = 5
Found: 3 + 1 + 1 = 5
Found: 4 + 1 = 5
Found: 4 + 1 = 5
The key is to understand what data you need to solve the problem. You need to know:
The target sum
(The sum of the elements so far)
The number and list of unchecked elements
The number and list of elements already in the list
The 'sum so far' can be derived from the number and list of elements already in the list, but it is convenient to pass it too. That gives a 6-parameter recursive function. It is invoked with the desired target, 0 as the sum so far, the complete array of elements to search, and an empty list that is big enough to hold all the elements to be searched. This happens in main(). The function identifies whether it found any lists that added up to the target (returning 0 if not and 1 if it did), hence the test and report and the end of main().
In the function, check for various impossible conditions and bail out. If compiled with debug = 1 at the top, print data on entry to the function. Scan through the remaining unchecked elements, detecting when the element makes the sum equal to the target and reporting the list that does so (note it loses the original index information; you can add that, but it is an exercise for the reader). If the element is small enough to leave space for another, add the element to the found list and pass the rest of the array to a recursive call to the function. The other functions are trivial printing loops.
When target is set to 40 (instead of 5) it correctly reports no subsets are found adding up to 40.
There probably are easier ways to code it, but I'm pathologically opposed to unnecessary global variables (I regard debug as a way of conditionally compiling the code more than as a global variable). It would be possible to package up the argument list in a structure; I'm not sure it would help all that much, though. I could use bool instead of int (and false and true instead of 0 and 1) if I included <stdbool.h>. The code is unrepentantly C99 or C11; it won't compile as written under C89 (but it wouldn't be hard to make it work with C89).
Code:
#include <stdio.h>
static const int debug = 0;
static void found_one(int num, int *list)
{
printf("Found: ");
char const *pad = "";
int sum = 0;
for (int i = 0; i < num; i++)
{
printf("%s%d", pad, list[i]);
pad = " + ";
sum += list[i];
}
printf(" = %d\n", sum);
}
static void print_array(char const *tag, int num, int *arr)
{
printf("%s (%d):", tag, num);
for (int i = 0; i < num; i++)
printf(" %d", arr[i]);
putchar('\n');
}
static int find_subsets(int target, int sumsofar, int num_src, int *src,
int num_dst, int *dst)
{
if (sumsofar >= target)
return 0;
if (num_src <= 0)
return 0;
if (debug)
{
printf("-->> %s: sumsofar = %d, num_src = %d, num_dst = %d\n",
__func__, sumsofar, num_src, num_dst);
print_array("Source", num_src, src);
print_array("Dest'n", num_dst, dst);
}
int rc = 0;
int max = target - sumsofar;
for (int i = 0; i < num_src; i++)
{
if (src[i] == max)
{
dst[num_dst] = src[i];
found_one(num_dst + 1, dst);
rc = 1;
}
else if (src[i] < max)
{
dst[num_dst] = src[i];
if (find_subsets(target, sumsofar + src[i], num_src - (i + 1),
src + (i + 1), num_dst + 1, dst))
rc = 1;
}
}
if (debug)
printf("<<-- %s: %d\n", __func__, rc);
return rc;
}
int main(void)
{
int data[] = { 3, 2, 4, 1, 1, 9 };
enum { NUM_DATA = sizeof(data) / sizeof(data[0]) };
int subset[NUM_DATA];
int target = 5;
print_array("Data", NUM_DATA, data);
if (find_subsets(target, 0, NUM_DATA, data, 0, subset) == 0)
printf("Did not find any subsets totalling %d\n", target);
return 0;
}