How do you call a variable in an array after sorting it in C++?

Question

What I am trying to do is to a variable in an array after sorting (ascending order) it through a function.

The function I have is:

void xpPoints_Sorting ()
{
  int xpPoints[] = { 620, 500, 250, 1000, 830, 100, 370 };
  int temp;

  for(int i=1;i< 7;++i)
    {
        for(int j=0;j<(7-i);++j)
            if(xpPoints[j] > xpPoints[j+1])
            {
                temp = xp[j];
                xpPoints[j] = xpPoints[j+1];
                xpPoints[j+1] = temp;
            }
    }
}

The problem is that when I type xpPoints[0], in int main(), the output is still "620" and not "100".

  int main()
  {
  xpPoints_Sorting ();
  int xpPoints[] = { 620, 500, 250, 1000, 830, 100, 370 };
  cout <<  xpPoints[0];
  }

However, when I take I don't put it in a function and put it in int main(), it works perfectly fine and outputs "100".

How can I get it to work while keeping the function for sorting the array?

xpPoints is local to main isnt't it? where you passed array to function? — Jayesh Bhoi
– Jayesh Bhoi, Commented May 12, 2017 at 4:46
What gave you the idea that it's the same array in main and xpPoints_Sorting? — StoryTeller - Unslander Monica
– StoryTeller - Unslander Monica, Commented May 12, 2017 at 4:53

Tim Biegeleisen · Accepted Answer · 2017-05-12 06:28:06Z

2

You seem to be confused about how scope works in C++. You defined an array in main() called xpPoints, but it is local to that function. Simply calling a function which sorts another array has no effect on your local xpPoints array. Hence, when you print the first element nothing has changed.

To remedy this, you can refactor xpPoints_Sorting() such that it takes an array as input and then sorts it, e.g.:

void xpPoints_Sorting (int xpPoints[], int length)
{
    int temp;

    for (int i=1; i < length; ++i)
    {
        for (int j=0; j < (length-i); ++j)
            if (xpPoints[j] > xpPoints[j+1])
            {
                temp = xp[j];
                xpPoints[j] = xpPoints[j+1];
                xpPoints[j+1] = temp;
            }
        }
    }
}

And then in your main() function:

int main()
{
    int xpPoints[] = { 620, 500, 250, 1000, 830, 100, 370 };
    xpPoints_Sorting(xpPoints, 7);
    cout << xpPoints[0];
}

edited May 12, 2017 at 6:28

answered May 12, 2017 at 4:47

Tim Biegeleisen

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5 Comments

Confused.Student Over a year ago

I have tried doing that but an error shows up and says "declaration of 'int xpPoints []' shadows a parameter"

Tim Biegeleisen Over a year ago

@Confused.Student Remove the unnecessary declaration of the xpPoints array from your sorting function, q.v. my update code above.

Confused.Student Over a year ago

Oh, I see. Thank you very much! I understand it now.

slawekwin Over a year ago

I think it's important to note, that it is (at least) useful to pass the length of the array to the function as well, instead of hardcoding it.

Tim Biegeleisen Over a year ago

@slawekwin Good thinking.

J Mkdjion · Accepted Answer · 2017-05-12 05:00:06Z

1

In idomatic C++ what you're trying to do can be achieved like so using the std::sort algorthim:

  #include <algorithm>

  int main()
  {
     int xpPoints[] = { 620, 500, 250, 1000, 830, 100, 370 };
     std::sort(xpPoints,xpPoints + 7);
     cout << xpPoints[0];
  }

answered May 12, 2017 at 5:00

J Mkdjion

3413 silver badges12 bronze badges

1 Comment

Confused.Student Over a year ago

I am not sure if my teacher will allow me to use that but thank you!

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