Sorting an array of strings in C++

Question

I am trying to accomplish the following task:

List the students in alphabetic order, sorted by last name. Do not change the given case of the names. Do not change the output file format. (Firstname Lastname) Just print the records in order by last name, i.e.

Annie J

Martin K

Toby L

This sort needs to be true alphabetical (not just the "lexicographical" sort).

The data was read in from a file and passed through a virtual function depending on what course this student was enrolled in. Here's what I have.

for (int i = 1; i < numStudents; i++)
{
   if (( list[i] -> getLastname() ) < ( list[i - 1] -> getLastname() ))
   { 
       Student *temp = list[i - 1];
       ist[i - 1] = list[i];
       list[i] = temp;
   }
}

I've been working on this for a while now and I'm worried I've gone about this all wrong. Any tips/pointers appreciated!

You've (basically) implemented the inner loop of a bubble sort. That's not enough to sort anything. Why not use std::sort? It also appears that your program is likely to access outside the bounds of your list array, which is pretty dangerous too. — Carl Norum
– Carl Norum, Commented Apr 8, 2015 at 1:18
sorry, I am somewhat new to programming and still trying to get a hang of the string functions. I'll take a look! Thanks! — JMoore
– JMoore, Commented Apr 8, 2015 at 1:20
Then just expand your loop into a proper sort. Check wikipedia for examples for any number of sorting algorithms. — Carl Norum
– Carl Norum, Commented Apr 8, 2015 at 1:39
Also note that operator< will do a lexicographic comparison. So "amy" will compare greater than "Tom" because 'a' (ASCII 97) is greater than 'T' (ASCII 84). — Miles Budnek
– Miles Budnek, Commented Apr 8, 2015 at 1:49

Eric Pruneau · Accepted Answer · 2015-04-08 01:40:45Z

1

I assume you have a struct like:

struct Student
{
    std::string m_LastName;
    std::string m_FirstName;
};

Now you need to make sure you can handle the case where two person have the same last name. In that case you want to look at the first name.

bool NameCompare(const Student &name1, const Student &name2)
{
    if(name1.m_LastName == name2.m_LastName) {
        return name1.m_FirstName < name2.m_FirstName;
    }

    return name1.m_LastName < name2.m_LastName;

}

Then just call sort on your list of Student

std::list<Student> student_list;
// add some Student to the list
student_list.sort(NameCompare);

answered Apr 8, 2015 at 1:40

Eric Pruneau

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Community · Accepted Answer · 2017-05-23 12:28:25Z

0

Use string comparison function instead of the less than sign you used here:

if (( list[i] -> getLastname() ) < ( list[i - 1] -> getLastname() ))

Also here's a similar stackoverflow question (partially)

Is string::compare reliable to determine alphabetical order?

edited May 23, 2017 at 12:28

CommunityBot

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answered Apr 8, 2015 at 1:35

Sed 'serdarsenay'

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1 Comment

Sed 'serdarsenay' Over a year ago

string comparison as in string::compare, ie: stringA.compare(stringB)

Noobie · Accepted Answer · 2022-04-21 15:06:17Z

0

Try this reference, first you have to declare the size of the array of firstname and lastname using int z = sizeof(lastname, firstname)/sizeof(lastname[0], firstname[0]); and using sort(lastname,lastname+z); will sort the array of lastname then using loop to print the firstname with the sorted lastname.

#include <string>
#include <algorithm>
#include <iostream>
using namespace std;

int main()
{
string firstname[] = {"Michael", "Patricia", "Joseph", "Elizabeth", "Charles", "Barbara", "Thomas", "Margaret", "Robert", "Sarah"};
string lastname[] = {"Smith", "Johnson", "Williams", "Brown", "Jones", "Miller", "Davis", "Garcia", "Rodriguez", "Wilson"};

int z = sizeof(lastname, firstname)/sizeof(lastname[0], firstname[0]);

sort(lastname,lastname+z); //Use the start and end like this
for(int y = 0; y < z; y++){
cout << firstname[y]<< " " << lastname[y] << endl;
}
return 0;
}

edited Apr 21, 2022 at 15:06

answered Apr 20, 2022 at 20:37

Noobie

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1 Comment

Cristik Over a year ago

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