Recursively storing integers in an array - c++

Question

I have problem with recursive functions.
I have to build a recursive function which creates an array of integer values corresponding to the digits of a given number.
For example, if I input a number like 3562, it should look like :
myArray[0] = 3
myArray[1] = 5
myArray[2] = 6
myArray[3] = 2
Here is my code :
#include <iostream>
using namespace std;
int myFunction(int num, int lenOfNum);
int main(){
int number;
int lengthCount = 0;
cout <<"Input numbers" << endl;
cin >> number;
int temp = number;
for(; number != 0; number /= 10, lengthCount++);
number = temp;
cout << myFunction(number, lengthCount) << endl;
}
int myFunction(int num, int lenOfNum){
int arr[lenOfNum];
if(num > 0){
for(int i = 0; i < lenOfNum; i++){
arr[i] = num/=10;
cout << "arr[" << i + 1 << " ]= " << arr[i] << endl;
}
return myFunction(num, lenOfNum);
}
else if(num == 0){
return 0;
} else;
}

Answer 1

The problem with your code is that you are calling int arr[lenOfNum] in each method call, which in short creates an array with a new reference to a memory location that can store lenOfNum integers.
To solve this, we declare the array in the main method and pass it as a parameter to the function.
int main() {
// somewhere in main after reading lenOfNum
int arr[lenOfNum];
// somewhere in main after declaring an array
myFunction(arr, number, lengthCount - 1);
}
and myFunction as
void myFunction(int *arr, int num, int idx) {
if (idx < 0) return; // you've completed processing the num
else if (num == 0) {
arr[0] = 0;
return;
}
arr[idx--] = num % 10;
myFunction(arr, num / 10, idx);
}

Answer 2

Using vector and rest part of your example
#include <iostream>
using namespace std;
void myFunction(vector<int> &arr, int num, int lenOfNum){
if (num < 0) {
return;
}
else if (num == 0) {
return;
}
int next_idx = lenOfNum - 1;
int digit = num % 10;
arr[next_idx] = digit;
myFunction(arr, num / 10, next_idx);
}
int main(){
int number;
int lengthCount = 0;
cout <<"Input numbers" << endl;
cin >> number;
int temp = number;
for(; number != 0; number /= 10, lengthCount++);
number = temp;
auto arr = vector<int>(lengthCount, 0);
myFunction(arr, number, lengthCount);
for(int i = 0; i < arr.size(); i++){
cout << "arr[" << i << " ]= " << arr[i] << endl;
}
}

Answer 3

Works for positive numbers
#include <vector>
#include <stdio.h>
std::vector<int> myFunction(int num)
{
std::vector<int> ret;
int irec = num / 10;
if (irec > 0)
ret = myFunction(irec);
ret.push_back('0' + (num % 10));
return ret;
}
int main(int argc, char *argv[])
{
std::vector<int> res = myFunction(539);
for(unsigned int i = 0; i < res.size(); i++)
printf("%c,", res[i]);
}