How can I sort in descending order? - c++

Question

I'm trying to sort for the top and second top value of totalRevenue and its name. I've tried to sort them in descending order this way but I could not figure it out how to make it work. Can anyone please help me out?
First two entries:
1002 Hammer 23.65 203
1024 Nails 6.95 400
Here is the code:
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
// Structure to hold statistics
struct Selling {
int productNumber;
string name;
double price;
int soldNumber;
double totalRevenue[];
};
int main()
{
ifstream statFile;
string productName;
double price;
int productNumber, soldNumber;
Selling *productArray[100];
Selling *aSelling;
int numProduct = 0;
int man = 0;
statFile.open("sales.txt");
while (numProduct < 100 && statFile >> productNumber >> productName >> price >> soldNumber)
{
Selling *aSelling = new Selling;
aSelling->productNumber = productNumber;
aSelling->name = productName;
aSelling->price = price;
aSelling->soldNumber = soldNumber;
aSelling->totalRevenue[] = aSelling->price * aSelling->soldNumber;
productArray[numProduct++] = aSelling;
//cout << aSelling->productNumber<< " " << aSelling->name << " " << aSelling->price << " " << aSelling->soldNumber << " " << aSelling->totalRevenue << endl;
}
for (int i = 0; i < 5; i++) {
for (int j = 0; j < 5; j++) {
if (aSelling->totalRevenue[i] > aSelling->totalRevenue[j]) {
man = aSelling->totalRevenue[i];
aSelling->totalRevenue[i] = aSelling->totalRevenue[j];
aSelling->totalRevenue[i] = man;
}
}
}
for (int i = 0; i < 2; i++) {
cout << "The top selling product is " << aSelling->name << "with total sales of " << aSelling->totalRevenue[i] << endl;
cout << "The second top selling product is " << aSelling->name << "with total sales of " << aSelling->totalRevenue[i - 1] << endl;
}
}
And there is an unexpected expression error at the line aSelling->totalRevenue[] = aSelling->price * aSelling->soldNumber; which I don't understand.

Answer 1

There is some confusion on the arrays to sort:
you should define totalRevenue as a double, not an array of doubles,
should be sort the first numProduct elements of the array productArray based on the criteria totalRevenue and name, the order is determined by the comparison operator used. Only compare the second criteria if the first criteria give equal values.
Here is a modified version:
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
// Structure to hold statistics
struct Selling {
int productNumber;
string name;
double price;
int soldNumber;
double totalRevenue;
};
int compareSellings(const Selling *a, const Selling *b) {
// sort in decreasing order of totalRevenue
if (a->totalRevenue > b->totalRevenue) return -1; // a comes before b
if (a->totalRevenue < b->totalRevenue) return +1; // b comes before a
// sort in increasing order of name for the same totalRevenue
if (a->name < b->name) return -1; // a comes before b
if (a->name > b->name) return +1; // b comes before a
return 0;
}
int main() {
ifstream statFile;
string productName;
double price;
int productNumber, soldNumber;
Selling *productArray[100];
int numProduct = 0;
statFile.open("sales.txt");
while (numProduct < 100 && statFile >> productNumber >> productName >> price >> soldNumber) {
Selling *aSelling = new Selling;
aSelling->productNumber = productNumber;
aSelling->name = productName;
aSelling->price = price;
aSelling->soldNumber = soldNumber;
aSelling->totalRevenue = price * soldNumber;
productArray[numProduct++] = aSelling;
//cout << aSelling->productNumber<< " " << aSelling->name << " "
// << aSelling->price << " " << aSelling->soldNumber << " "
// << aSelling->totalRevenue << endl;
}
for (int i = 0; i < numProduct; i++) {
for (int j = 0; j < numProduct; j++) {
if (compareSellings(productArray[i], productArray[j]) > 0) {
Selling *aSelling = productArray[i];
productArray[i] = productArray[j];
productArray[j] = aSelling;
}
}
}
cout << "The top selling product is " << productArray[0]->name
<< ", with total sales of " << productArray[0]->totalRevenue << endl;
cout << "The second selling product is " << productArray[1]->name
<< ", with total sales of " << productArray[1]->totalRevenue << endl;
return 0;
}
Further remarks:
you might use a more efficient sorting method
you should free the allocated objects
you should use <algorithms> and dynamic arrays of objects instead of allocating the objects with new and manipulating naked pointers.
you should handle exceptions