Running a sorting function on array, but something isnt working properly as I am not getting any output

[soggymuskrat]

I have an array of pointers that point to structs each of which have a set of variables name, id, grade, and hometown.

We are to create functions to sort that array based on those variables.

I have created a function to sort by grade, but when I run the sort and then attempt to display the array it still comes out unsorted, with my output will look like:

Bob        10170        B      Bali
Al         1041         A      Anchorage
Cindy      7964         C      Cerritos

It is still unsorted by the last category, and just prints them in the order I entered them.

Here is my sortingByHometown method:

    void sortbyHometown(Student *SP[])
    {
        for (int i = 0; i < 3; i++) {

            if (SP[i]->hometown > SP[i + 1]->hometown) {

                int x = SP[i]->hometown.compare(SP[i + 1]->hometown);

                if (x < 0)
                    swap(SP[i], SP[i + 1]);

            }
        }
    }

The reason I have it as i < 3 is that I am only testing when I have created 3 structs to be pointed to, just a heads up.

Also, just a heads up, this is an assignment so I have to stay in the confines of my methods and array of pointers.

Just to break down my process for getting to the sorting function too.

Initialize array of pointers to my struct (Students) size 10 (Line 27)
Create a populate fuction to populate the array with structs (This calls my initStudent which allows me to set the instance variables (Line 50)
Sort the array by hometown (Line 62, called in main on Line 30)
Here is my code, if I can get any assistance on why function isn't properly sorting that would be much appreciated, tahnks for reading!

  #include<iostream>
#include <stdlib.h> 
#include<string>
#include<iomanip>

using namespace std;

    struct Student
    {
        char name[20];
        int SID;
        char grade;
        string hometown;

    };

    void initStudent(Student &SR);
    void swap(int, int);
    void display(Student*[]);
    void populate(Student*[]);
    void sortbyHometown(Student *SP[]);

    int main() {

        // Create and array of pointers to students size 10

        Student *S[10];

        populate(S); // Pass in array of pointers S
        sortbyHometown(S);
        display(S);

        system("pause");
        return 0;

    }

    void display(Student * S[]) {

        for (int i = 0; i < 10; i++) {

            cout << S[i]->name << setw(10) << S[i]->SID << setw(10) << S[i]->grade << setw(10) << S[i]->hometown << endl;
            //s[i]->bday.display();
            //cout << "\n" << s[i]->hometown << endl;

        }

    }

    void populate(Student *S[]) {

        // Can also use local[] as a parameter, they are the SAME THING

        for (int i = 0; i < 3; i++) {
            S[i] = new Student;
            initStudent(*S[i]);
        }
    }



    void sortbyHometown(Student *SP[])
    {
        for (int i = 0; i < 2; i++) {

            if (SP[i]->hometown > SP[i + 1]->hometown) {

                int x = SP[i]->hometown.compare(SP[i + 1]->hometown);

                if (x < 0)
                    swap(SP[i], SP[i + 1]);

            }
        }
    }

[Handy Andy]

Hello soggymuskrat,

Welcome to the forum.

I tried to compile and run your program, but I am missing the function "initStudent" and technically the function "swap" is missing, but this in not a problem because of line 6 the compiler is using "std::swap()" from the utility header file. I am thinking that the utility header file must be included in one of the C++ header files that you did include. And yes this is a good example of why using namespace std; is a bad idea.

I will have to try something different to test your sort function to see what is happening.

It does puzzle me why you are doing two different types of compares just to get to the swap function call?

I was also wondering why in your struct you use a character array for the name, but a std::string for the home town? I would use a std::string for both.

Do not know if that will help yet,

Andy

[soggymuskrat]

Hey Andy, got it to work, here is my code in case anyone else comes across this question:

	void sortbyHometown(Student *S[])
	{
		for (int i = 0; i < 9; i++)
		{ // i < 9 so last element isnt trying to check S[11]

			for (int j = 0; j < 9; j++) {
				int x = S[j]->hometown.compare(S[j + 1]->hometown); // Integer value comparison

				if (x > 0) { // If value is less than, swap, if not check nexxt index 
					swap(S[j], S[j + 1]);
				}
			}

		}	
	}

I basically needed the nested loop, and this is essentially a bubblesort algo.

Really appreciate the response on this!