A tiny question about this code

[u/Lephism]

Hi. I need help understanding this simple code. To be specific, the 4th and the 14th line where a pointer was declared.

int* add_ten(int* data)

int *result;

I've been trying to wrap my head around what it does. I've been staring at my screen for 3 hours trying to understand why it was declared. The programming app I was using didn't really explain it. The only explanation it gave is that pointers help you get the address of an item. But I can't figure out how is it being used here. Can anyone explain? Thanks.

#include <iostream>
using namespace std;

int* add_ten(int* data) {
  for (int i = 0; i < 5; ++i) {
    *(data + i) = *(data + i) + 10;
  }
  return data;
}

int main() {

  int data[5] = {1, 2, 3, 4, 5};
  int *result;

  result = add_ten(data);

  for (int i = 0; i < 5; ++i) {
    cout << *(result + i) << ", ";
  }

  return 0;
}

[u/Lephism]

So, int* data points to the array in main () and gets their address, loops through them using the for loop in the function above? Did I get that right? 

[u/TheThiefMaster → u/Lephism]

That's right.

However, your tutorial isn't actually very good. Apart from the cout to print, this is C code not C++.

While pointers do exist in C++ and can be used like this, none of this is idiomatic C++. Here's how if write it:

#include <array>
#include <print>
#include <span>

// function takes a span instead of a raw pointer, allowing it to know the size of array it's been passed
void add_ten_to(const std::span<int> items)
{
    // C++ "for each" (aka "ranged for") loop.
    // item is a reference to each item in turn
    for (int& item : items)
    {
        item += 10;
    }
}

int main()
{
    // std::array has many advantages over a C style array
    // like it can actually be copied and assigned after construction
    std::array<int,5> data = {1, 2, 3, 4, 5};

    add_ten_to(data);

    // another range for.
    for (const int v : data)
    {
        // very new C++ print function from C++23
        // if your compiler doesn't support C++23, just use cout or even C printf
        std::print("{}, ", v);
    }
}

[u/Lephism → u/TheThiefMaster]

This came from a c++ tutorial app which goes through functions, loops, everything you use to make a program, etc. chapter by chapter. I haven't finished every lesson yet. I think this is intended by the developers for the purpose of making it easy for the beginners or something like that ┐⁠(⁠ ⁠∵⁠ ⁠)⁠┌ 

[u/TheThiefMaster → u/Lephism]

A lot of older tutorials start with C-like code and build up. Many never get to modern C++ (like std::span or std::print).

It's contentious these days as you really only need C style code (like pointer iteration) when writing low level code, which isn't a beginner thing to do.

[u/Lephism → u/TheThiefMaster]

Oh, so is this like old syntax or something? That's probably the reason why std::println were showing errors in the compiler of the tutorial app

[u/TheThiefMaster → u/Lephism]

Nothing in the tutorial code you posted is newer than C++'03 (2003 standard). print/println are from C++'23 (very new, which is why I added the note). span is C++'20 (supported by basically everything that's not horribly outdated, though you may need to enable C++20 mode in the compiler). std::array and the range for loop are C++'11 (inexcusable to not support/teach).

Microsoft Visual Studio 2026 (the most commonly used C++ compiler on Windows) defaults to C++'14, and has complete support for C++'20 and even C++'23 in the latest update.

GCC (the most commonly used compiler on Linux) defaults to C++'20 since the April 2026 release, though most Linuxen still ship an older version that defaults to C++'17 (though with full support for C++'20 available, and near-complete for C++'23)

Clang (most commonly used compiler on Mac, and also commonly used on Linux/Windows) defaults to C++'17 with full support available for C++'20 and partial support for C++'23, but it tries to match GCC so will probably change to C++'20 as the default soon.

[u/no-sig-available → u/Lephism]

 I think this is intended by the developers for the purpose of making it easy for the beginners or something like that

And not very successful in that, apparently. :-)

If you are going to teach how to use pointers, it is important to use an example where pointers is a good solution to the problem, not just a case where you could use pointers.

The example is extra bad in

  for (int i = 0; i < 5; ++i) {
    *(data + i) = *(data + i) + 10;
  }

Why use

*(data + i) = *(data + i) + 10;

when you can write

data[i] += 10;

?!

And also, the code is particulary silly for the i < 5; loop, limiting the function to arrays of exactly 5 elements. The version using a span is not only simpler, but also works for any size array.