Sorting a 2D Char and Int Array from class using bubble sort?

Question

I am trying to sort an array of int and char s (from a class) by descending order. These are student names and grades.

The class is defined as:

class Student {
public:
    char name[20];
    int grades;
};

numCount is the incremental value of number of records.

void bubble_sort(Student theResults[], int numCount)
{
  bool swapped = true;
  while(swapped)
  {
    swapped = false;
    for(int i=1;i<numCount;i++)
    {
      if(theResults[i-1].grades < theResults[i].grades)
      {
        int tempHold = theResults[i-1].grades;
        theResults[i-1].grades = theResults[i].grades;
        theResults[i].grades = tempHold;
        swapped = true;
      }
    }
  }

The issue I am having is that the int values (grades) are sorted correctly after the loop but having difficulty getting the names to be correctly allocated to match with the grades.

I have used the following code but it doesn't work as it displays the incorrect grades for the students.

char* title_temp = theResults[i-1].name;
theResults[i-1].name[20] = theResults[i].name[20];
theResults[i].name[20] = title_temp[20];

Answer 1

The problem is that you need to swap the objects , the grades only have to act as a key to guide the sort, try this :

void bubble_sort(Student theResults[], int numCount)
{

    Student tempHold;
    bool swapped = true;
    while(swapped)
    {
        swapped = false;
        for(int i=1;i<numCount;i++)
        {
            if(theResults[i-1].grades < theResults[i].grades)
            {
                tempHold = theResults[i-1]; //swap the objects, not just the grades.

                theResults[i-1]= theResults[i];

                theResults[i] = tempHold;

                swapped = true;
            }
        }
    }}

However, if you must copy members, then in addition to swapping grades :

char temp[20];
strcpy(temp ,theResults[i-1].name);
strcpy(theResults[i-1].name,theResults[i].name);    
strcpy(theResults[i].name,temp);

Instead of using

    char* title_temp = theResults[i-1].name; // <-wrong
   theResults[i-1].name[20] = theResults[i].name[20];//20 is invalid index
    theResults[i].name[20] = title_temp[20]; //this is just 1 element out of the whole array

which is wrong due to many reasons.

Answer 2

You'd have to copy the entire char block, each element at a time using a loop, or you could use memcpy.

You could also use a shallow copy of your class

void bubble_sort(Student theResults[], int numCount)
{


    bool swapped = true;
    while(swapped)
    {
        swapped = false;
        for(int i=1;i<numCount;i++)
        {
            if(theResults[i-1].grades < theResults[i].grades)
            {
                Student tempHold = theResults[i-1];

                theResults[i-1]= theResults[i];

                theResults[i] = tempHold;

                swapped = true;
            }
        }
    }
}

Answer 3

I think your problem is here:

if(theResults[i-1].grades < theResults[i].grades)
{
    int tempHold = theResults[i-1].grades;

    theResults[i-1].grades = theResults[i].grades;

    theResults[i].grades = tempHold;

    swapped = true;
}

What you really want to do is

if(theResults[i-1].grades < theResults[i].grades)
{
    Student tempHold = theResults[i-1];

    theResults[i-1] = theResults[i];

    theResults[i] = tempHold;

    swapped = true;
}

Before all you were changing was the grade value and not the names, this will switch the entire Student object and should produce the output you are looking for