How to sort an array of structures based on a field in the structures? (in C)

Question

I have a program that stores a variety of information about 10 universities as structures in an array. I have a function named 'inputData' that loads the information of the universities into the array by converting them to structures. I am trying to write a function that will sort the universities by tuition (from highest to lowest). I tried to use selection sort to do this, but I keep running into an error somewhere down the line.

This is the structure:

struct University
{
    char name[50];
    char city[20];
    char state[3];
    int rank;
    int tuition;
};

This is the function to convert info to a structure:

struct University inputData(char Name[50], char City[20], char State[3], int Rank, int Tuition){
    struct University uni;
    strcpy(uni.name, Name);
    strcpy(uni.city, City);
    strcpy(uni.state, State);
    uni.rank=Rank;
    uni.tuition=Tuition;
    return uni;
};

Then I created a structure array and added all the info:

struct University university[10];
university[0]= inputData("Princeton University", "Princeton", "NJ", 1, 45320);
university[1]= inputData("University of Virginia", "Charlottesville", "VA", 24, 52040);
university[2]= inputData("Boston College", "Chestnut Hill", "MA", 31, 51296);
university[3]= inputData("Georgia Institute of Technology", "Atlanta", "GA", 34, 32404);
university[4]= inputData("Lehigh University", "Bethlehem", "PA", 44, 48320);
university[5]= inputData("University of Chicago", "Chicago", "IL", 3, 52491);
university[6]= inputData("Duke University", "Durham", "NC", 8, 51265);
university[7]= inputData("University of Georgia", "Athens", "GA", 56, 29844);
university[8]= inputData("University of Denver", "Denver", "CO", 86, 46362);
university[9]= inputData("Loyola University Chicago", "Chicago", "IL", 99, 26270);

I'm trying to sort using this function (which uses selection sort):

void printSortedUniversity(struct University* list){
    int i, j, max_idx; 
  
      for (i = 0; i < 9; i++) 
    { 
        max_idx = i; 
        for (j = i+1; j < 10; j++) 
          if (list[j].tuition > list[max_idx].tuition) 
            max_idx = j; 
  
        swap(&list[max_idx], &list[i]); 
    } 
    
    for (i=0; i<10; i++){
        printInfo(list[i]);
        printf("\n");
    }
};

And this is the swap function:

void swap(int *x, int *y) 
{ 
    int temp = *x; 
    *x = *y; 
    *y = temp; 
}

I keep getting:

Name: Univceton University City: Princeton State: NJ Rank: 1 Tuition: 45320
Name: Prinersity of Virginia City: Charlottesville State: VA Rank: 24 Tuition: 52040
Name: Univon College City: Chestnut Hill State: MA Rank: 31 Tuition: 51296
Name: Bostgia Institute of Technology City: Atlanta State: GA Rank: 34 Tuition: 32404
Name: Georgh University City: Bethlehem State: PA Rank: 44 Tuition: 48320
Name: Lehiersity of Chicago City: Chicago State: IL Rank: 3 Tuition: 52491
Name: Duke University City: Durham State: NC Rank: 8 Tuition: 51265
Name: University of Georgia City: Athens State: GA Rank: 56 Tuition: 29844
Name: University of Denver City: Denver State: CO Rank: 86 Tuition: 46362
Name: Loyola University Chicago City: Chicago State: IL Rank: 99 Tuition: 26270

I don't understand why the names get corrupted and why the sort doesn't work? I think it's because the modified list isn't being stored anywhere but I have no idea how to fix this. Any help would be appreciated. Thank You

Do you need to write your own sort or can you just use qsort? — tadman
– tadman, Commented Dec 2, 2020 at 2:05
This code assumes you have a fixed number of entries. Always use an argument to convey exactly what is going on. — tadman
– tadman, Commented Dec 2, 2020 at 2:05
Tip: Declare your iterator variables inside the scope in which they're used. Like for (int i = 0; ...) helps keep things contained. — tadman
– tadman, Commented Dec 2, 2020 at 2:06
@kashmafia Why are you putting a ; at the end of the block of inputData() function and printSortedUniversity() function? — Shubham
– Shubham, Commented Dec 2, 2020 at 2:14

score 2 · Accepted Answer · 2020-12-02 02:32:32Z

2

You swap function should be

void swap(struct University *x, struct University *y) 
{ 
    struct University temp = *x; 
    *x = *y; 
    *y = temp; 
}

This gives the expected output:

Name: University of Chicago City: Chicago Rank: 3 Tuition: 52491
Name: University of Virginia City: Charlottesville Rank: 24 Tuition: 52040
Name: Boston College City: Chestnut Hill Rank: 31 Tuition: 51296
Name: Duke University City: Durham Rank: 8 Tuition: 51265
Name: Lehigh University City: Bethlehem Rank: 44 Tuition: 48320
Name: University of Denver City: Denver Rank: 86 Tuition: 46362
Name: Princeton University City: Princeton Rank: 1 Tuition: 45320
Name: Georgia Institute of Technology City: Atlanta Rank: 34 Tuition: 32404
Name: University of Georgia City: Athens Rank: 56 Tuition: 29844
Name: Loyola University Chicago City: Chicago Rank: 99 Tuition: 26270

Note

This is an extremely inefficient sort. No one would do this in production code.

edited Dec 2, 2020 at 2:32

answered Dec 2, 2020 at 2:16

user3657941

Sign up to request clarification or add additional context in comments.

2 Comments

Surt Over a year ago

Selection sort at least have one positive, the low number of swaps.

user3657941 Over a year ago

It would be cheaper to swap pointers. Copying the whole struct is the real problem.

Shubham · Accepted Answer · 2020-12-04 01:26:06Z

1

As David Cullen wrote about the swap() function in their answer, the swap() function to interchange structures according to tuition would be:

void swap(struct University *x, struct University *y) 
{ 
    struct University temp = *x; 
    *x = *y; 
    *y = temp; 
}

and your printSortedUniversity() function should be like this:

void printSortedUniversity(struct University* list){
    int i, j, max_idx;

      for (i = 0; i < 9; i++)
    {
        max_idx = i;
        for (j = i+1; j < 10; j++)
            if (list[j].tuition > list[max_idx].tuition)
                max_idx = j;
        if(i != max_idx)
            swap(&list[max_idx], &list[i]);
    }

    for (i=0; i<10; i++){
        printInfo(list[i]);
        // printf("%d\n",list[i].tuition);
        printf("\n");
    }
}

edited Dec 4, 2020 at 1:26

answered Dec 2, 2020 at 2:32

Shubham

1,15310 silver badges21 bronze badges

2 Comments

Surt Over a year ago

Don't you miss some {} or your indention is wrong?

Shubham Over a year ago

@Surt Sorry, It is the indention.

trufflewaffle · Accepted Answer · 2020-12-02 18:30:47Z

0

This is what worked for me:

Used this swap function:

void swap(struct University *p, struct University *q)  //function to swap list items
{ 
    struct University hold = *p; 
    *p = *q; 
    *q = hold; 
}

And I didn't change the printSortedUniversity function:

void printSortedUniversity(struct University* list){ int i, j, max_idx;

  for (i = 0; i < 9; i++) 
{ 
    max_idx = i; 
    for (j = i+1; j < 10; j++) 
      if (list[j].tuition > list[max_idx].tuition) 
        max_idx = j; 

    swap(&list[max_idx], &list[i]); 
} 

for (i=0; i<10; i++){
    printInfo(list[i]);
    printf("\n");
}

};

edited Dec 2, 2020 at 18:30

answered Dec 2, 2020 at 17:51

trufflewaffle

17912 bronze badges

1 Comment

Surt Over a year ago

Now you just need to accept one of the answers.

Collectives™ on Stack Overflow

How to sort an array of structures based on a field in the structures? (in C)

3 Answers 3

2 Comments

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related