Using 4 lists, create a list of all sums - c++

Question

I am beginner in C++ and have been trying to get an output of all the sums from 4 different lists of numbers. I want to know all the possible sums using up to 1 from each list. Repeats can be omitted.
For example with an input of [1, 2], [1, 3], [2, 3], [2, -1] should output [-1, 0, 1, 2, 3, ... 10].
My lists are 4, 6, 6, and 9 digits long, should that make a difference?
I have tried
#include<bits/stdc++.h>
using namespace std;
void subsetSums(int arr[], int l, int r,
int sum=0)
{
// Print current subset
if (l > r)
{
cout << sum << " ";
return;
}
subsetSums(arr, l+1, r, sum+arr[l]);
subsetSums(arr, l+1, r, sum);
}
int main()
{
int arr[] = {7, 14, 21, 28}, {-10, -20, -30, -40, -50, -60};
int n = sizeof(arr)/sizeof(arr[0]);
subsetSums(arr, 0, n-1);
return 0;
}
But it only produces an error:
expected unqualified-id before ‘{’ token
int arr[] = {5, 4, 3}, {4, -1, 5};

Answer 1

The simplest mechanism would be to create an array of all possible sums, and then remove duplicates.
#include <algorithm>
#include <iostream>
#include <vector>
int main() {
std::vector<std::vector<int>> arrs = {
{7, 14, 21, 28},
{-10, -20, -30, -40, -50, -60},
{50, 90}
};
// Let's start with 0 in the results, as if we used no value from any of
// the arrays
std::vector<int> results = {0};
// Append new sums to the results list
for (const auto &arr : arrs) {
const int length = results.size();
for (int i = 0; i < length; i++)
for (int j = 0; j < arr.size(); j++)
results.push_back(results[i] + arr[j]);
}
// Remove duplicates
std::sort(results.begin(), results.end());
results.erase(
std::unique(results.begin(), results.end()),
results.end());
// Print the results
for (int value : results)
std::cout << value << " ";
std::cout << "\n";
}

Answer 2

Let us parse the line
int arr[] = {7, 14, 21, 28}, {-10, -20, -30, -40, -50, -60};
This is a variable definition. The type is int. The first variable being defined is arr, which due to the [] is actually an array with the size to be determined by the initialization. The = starts the initialization. The {7, 14, 21, 28} gives the four values to be stored in the array and at the same time determines that the array has four elements. The , says "I'm done defining that variable and moving on to the next variable of the same basic type". There is no name for this next variable, hence the error. The {-10, -20, -30, -40, -50, -60} would define the initial values for another array, but since you did not name another variable, the compiler gets rather confused.
One way to define two arrays is like:
int arr[] = {7, 14, 21, 28}, other_array[] = {-10, -20, -30, -40, -50, -60};
but using two lines often works out better for the human reader (the below means the same thing as the above)
int arr[] = {7, 14, 21, 28};
int other_array[] = {-10, -20, -30, -40, -50, -60};
Since you need four lists, you probably will end up with something like:
int arr1[] = {7, 14, 21, 28};
int arr2[] = {-10, -20, -30, -40, -50, -60};
int arr3[] = {-15, -25, -35, -45, -55, -65};
int arr4[] = {1, 2, 3, 4, 5, 6, 7, 8, 9};
Note that you will have four lengths to keep track of. This is where std::array can become convenient.