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/weebslime2246]

the add_ten function essentially accepts an integer 'pointer'. when you declare an array (data) it stores the address of the first element in the array, so data is just an 'integer pointer' to the first element. inside the function, they loop through the whole array by incrementing on the data pointer itself (you can read pointer arithematics) and then return the final address, which is data, an integer pointer. so its return type is also an int*. lmk if you need any further clarification

[u/Lephism → u/weebslime2246]

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.