Printing Value From Array in C++ - c++

Question

I want to write a method in C++ which creates an array of monotonically increasing values. It has the inputs of int begin, int end, int interval.
In this example; method should return the array of [0,1,2,3,4,5,6,7,8,9,10]. When I print the results it should print out the first two indexes and get 0 and 1. However, when I print it, it gives 0 for the first one and 9829656 for the second one.
When I only print one index it is always correct, but when I print more than one index, every value except for the first printed one gives a different result. I think the other results are related to memory address since I used pointers.
#include <iostream>
using namespace std;
int* getIntervalArray(int begin, int end, int interval){
int len = (end - begin) / interval + 1;
int result[11] = {};
for (int i = 0; i <= len - 1; i++) {
result[i] = begin + interval * i;
}
return result;
}
int main(){
int begin = 0;
int end = 10;
int interval = 1;
int* newResult = getIntervalArray(begin, end, interval);
cout << newResult[0] << endl;
cout << newResult[1] << endl;
return 0;
}

Answer 1

You are returning a pointer to a local variable. You can instead return a std::vector by value as shown below:
#include <iostream>
#include <vector>
//return a vector by value
std::vector<int> getIntervalArray(int begin, int end, int interval){
int len = (end - begin) / interval + 1;
std::vector<int> result(len); //create a vector of size len
for (int i = 0; i <= len - 1; i++) {
result.at(i) = begin + interval * i;
}
return result;
}
int main(){
int begin = 0;
int end = 10;
int interval = 1;
std::vector<int> newResult = getIntervalArray(begin, end, interval);
//print out elements of returned vector
for(int i = 0; i < newResult.size(); ++i)
{
std::cout << newResult.at(i) << std::endl;
}
return 0;
}
The output of the above program can be seen here.

Answer 2

A possible solution dynamically allocating the local array, and returning it via a smart pointer:
#include <array>
#include <iostream>
#include <memory> // make_unique
auto getIntervalArray(int begin, int end, int interval)
{
int len = (end - begin) / interval + 1;
auto result{ std::make_unique<std::array<int, 11>>() };
for (int i = 0; i <= len - 1; i++) {
(*result)[i] = begin + interval * i;
}
return result;
}
int main()
{
int begin = 0;
int end = 10;
int interval = 1;
auto newResult{ getIntervalArray(begin, end, interval) };
std::cout << (*newResult)[0] << std::endl;
std::cout << (*newResult)[1] << std::endl;
std::cout << (*newResult)[2] << std::endl;
return 0;
}
Demo

Answer 3

Set the array variable in your function as static. This is because C++ does not support returning the address of a local variable.
static int result[11];

Answer 4

try this. also add deletion of the newResult
#include <iostream>
using namespace std;
int* getIntervalArray(int begin, int end, int interval){
int len = (end - begin) / interval + 1;
int* result = new int[len];
int lastValue = begin;
for (int i = 0; i <= len - 1; i++) {
result[i] = lastValue;
lastValue += interval;
}
return result;
}
int main(){
int begin = 0;
int end = 10;
int interval = 1;
int* newResult = getIntervalArray(begin, end, interval);
cout << newResult[0] << endl;
cout << newResult[1] << endl;
// add delete here.
return 0;
}