Using qsort to output ordered list - c++

Question

I have an assignment in my C++ course to get information from a text file that says this:
Scores.txt
PhredrickTheGreat 5.7 5.3 5.1 5.0 4.7 4.8
RobbieTheRock 3.1 4.9 4.1 3.7 4.6 3.9
CannonBallKelly 4.1 5.3 4.9 4.4 3.9 5.4
MartyTheMissile 5.1 5.7 5.6 5.5 4.4 5.3
BillieBomb 5.9 4.8 5.5 5.0 5.7 5.7
JackKnifeJake 5.1 4.7 4.1 3.1 4.6 5.0
Splash 5.1 5.1 4.9 3.4 5.5 5.3
MillyTheMalard 4.9 4.3 5.2 4.5 4.6 4.9
HoraceTheDivingHorse 6.0 6.0 5.7 5.8 5.9 5.9
FishTank 4.3 5.2 5.9 5.3 4.3 6.0
These are the names of fictional baseball players (and batting scores?). The program should output the names of the players, their average score, and then assign them 1st, 2nd, 3rd, etc. place based on their average score. Here's what I have so far:
I commented out a couple of "couts," so you can ignore those.
#include <iostream>
#include <iomanip>
#include <fstream>
using namespace std;
struct Scores
{
float Score;
string Name;
};
float calculateAverage(float RawData){ return RawData / 6.0;}
int main()
{
string Name;
string Score;
float RawScores = 0;
float Average;
Scores ComScores[10];
ifstream playerData("Scores.txt");
for(int i = 0; i < 10; i++)
{
playerData >> Name; // Read in a name
//cout << left << setw(25) << Name << " ";
ComScores[i].Name = Name;
for(int j = 0; j < 6; j++) // Read in Six Scores
{
playerData >> Score;
RawScores += atof(Score.c_str());
//cout << Score << " ";
}
Average = calculateAverage(RawScores);
ComScores[i].Score = Average;
RawScores = 0;
//cout << " Ave: " << fixed << setprecision(2) << Average <<endl;
}
cout << "Place Name Score\n";
cout << "-------------------------------------\n";
for(int i=0; i < 10; i++)
{
if (i < 9){
cout << " " << i+1 << " " << setw(25) << ComScores[i].Name << " " << setw(8) << ComScores[i].Score << endl;
}
else{cout << i+1 << " " << setw(25) << ComScores[i].Name << " " << setw(8) << ComScores[i].Score << endl;}
}
cout << "\n";
cin.get();
return 0;
}
As you can see, I'm almost done I just have to order the places with qsort. My professor gave us one example of using qsort (which I can post), but it didn't really relate to this program (in my point of view). The programs already kinda big and complicated to a novice like me, so, I'm having trouble implementing qsort.
What can I add to my program to sort the last "for loop" to order the list?
I will answer any questions asap.

Answer 1

Here is a way you could do the comparison function :
int score_cmp(const void* a, const void* b)
{
const Scores* sa = (const Scores*)a;
const Scores* sb = (const Scores*)b;
if (sa->Score > sb->Score)
return -1;
else if (sb->Score > sa->Score)
return 1;
else
return 0;
}
And you would call qsort like this:
qsort((void*)ComScores, 10, sizeof(Scores), score_cmp);
That said, you should try to rewrite it yourself once you understand how it's supposed to work, it's not very hard and it's a good exercise.
But note that as #PaulMcKenzie pointed out, calling qsort with a non-trivial type is undefined behavior.
If you must use qsort, a simple but fairly ugly fix would be to replace the string member in struct Scores by a string* and then update the remaining code as needed (the qsort part would not have to change).