Selection Sort Swap Function

[natekelsey]

I keep looking back at my swap function inside my Selection Sort Function and I keep thinking that it's not right. I'm not sure why but I feel that I'm doing it wrong. Advice is appreciated.

// Called inside my selection_Sort()
  swap(Array[i], Array[index_Largest]);

// Swap Declaration in my header
 swap(int, int);

// Swap Definition in my class
 swap(int a, int b)
 {
   int temp = 0;
   temp = a;
   a = b;
   b = temp;
 }

[o3hC5Di1]

Hi there,

You're swapping elements of an array - so a and b should be positions in the array and you should pass in the array too:

// Called inside my selection_Sort()
  swap(Array[i], Array[index_Largest], Array);

// Swap Declaration in my header
 swap(int, int, int[]);

// Swap Definition in my class
 swap(int a, int b, int arr[])
 {
   int temp = arr[a];
   arr[a] = arr[b];
   arr[b] = temp;
 }

Hope that makes sense. Please do let us know if you have any further questions.

All the best,
NwN

[Catfish4]

The idea itself is good, but the function doesn't work because parameters a and b are passed by value.

This means that a and b are copied inside your swap() function as if they are local variables. For example temp is a local variable. So any way you change a and b does not affect the "real" variables that you want to swap.

How to fix this?

Method A: Do not pass by value, pass by reference instead.

swap(int &, int &);

// the code inside remains the same, because it is correct
swap(int &a, int &b)
{
   int temp = 0;
   temp = a;
   a = b;
   b = temp;
}

Method B: You are reinventing the wheel by creating your own swap() function. C++ already has one in the algorithm library.

#include <algorithm>

// ...

std::swap(Array[i], Array[index_Largest]);

// or

using namespace std; // bad habit

swap(Array[i], Array[index_Largest]);

http://www.cplusplus.com/reference/algorithm/swap/

[natekelsey]

Thanks guys. It's always the small things that tend to elude my mind.

[Catfish4]

It's always the small things that tend to elude my mind.

It's the same for pretty much everybody, with this thread being a perfect example.
Both I and NwN missed that your swap() function didn't have a return type.

void swap(int &a, int &b);