# [SOLVED] Sort struct array in lexicographical order

## Issue

I need to sort students according to their surname or if their surname is the same according to their name in lexicographical order.

``````#include <stdio.h>
struct Student {
char name[20], surname[20];
};
void sort(struct Student students[], int n) {
int i, j, temp;
for (i = 0; i < n; i++)
for (j = i + 1; j < n; j++)
if (students[j].surname > students[i].surname ||
students[j].name > students[i].name) {
temp = i;
students[i] = students[j];
students[j] = students[temp];
}
}
void main() {
struct Student students[6] = {
{"Mujo", "Mujic"},
{"Meho", "Mujic"},
{"Pero", "Peric"},
{"Beba", "Bebic"},
{"Mujo", "Mujic"},
{"Fata", "Fatic"},
};
sort(students, 6);
int i;
for (i = 0; i < 6; i++)
printf("%s %s\n", students[i].surname, students[i].name);
}
``````

This prints only one student six times. Could you help me to fix this?

• Note: using auxiliary arrays is not allowed

## Solution

Your swap code is dubious — broken, I believe. A big warning bell is the type of `temp` — it needs to be a `struct Student`.

You have:

``````    temp = i;
students[i] = students[j];
students[j] = students[temp];
``````

You need:

``````    struct Student temp = students[i];
students[i] = students[j];
students[j] = temp;
``````

Obviously, remove the definition `int temp;` as well.

However, there are other problems too (as ever). You can’t usefully compare strings using relational operators — use `strcmp()`. And your ordering test is wrong too, even when revised to use `strcmp()`.

This code does the job, sorting names in descending order:

``````#include <stdio.h>
#include <string.h>

struct Student
{
char name[20];
char surname[20];
};

static void sort(struct Student students[], int n)
{
for (int i = 0; i < n; i++)
{
for (int j = i + 1; j < n; j++)
{
int rc = strcmp(students[j].surname, students[i].surname);
if (rc > 0 ||
(rc == 0 && strcmp(students[j].name, students[i].name) > 0))
{
struct Student temp = students[i];
students[i] = students[j];
students[j] = temp;
}
}
}
}

static void dump_array(const char *tag, size_t size, const struct Student *students)
{
printf("%s (%zu):\n", tag, size);
for (size_t i = 0; i < size; i++)
printf("%s %s\n", students[i].surname, students[i].name);
}

int main(void)
{
struct Student students[] =
{
{"Mujo", "Mujic"},
{"Meho", "Mujic"},
{"Pero", "Peric"},
{"Zebra", "Elephant"},
{"Beba", "Bebic"},
{"Mujo", "Mujic"},
{"Abelone", "Shells"},
{"Fata", "Fatic"},
};
enum { NUM_STUDENTS = sizeof(students) / sizeof(students[0]) };

dump_array("Before", NUM_STUDENTS, students);
sort(students, NUM_STUDENTS);
dump_array("After", NUM_STUDENTS, students);

return 0;
}
``````

Output:

``````Before (8):
Mujic Mujo
Mujic Meho
Peric Pero
Elephant Zebra
Bebic Beba
Mujic Mujo
Shells Abelone
Fatic Fata
After (8):
Shells Abelone
Peric Pero
Mujic Mujo
Mujic Mujo
Mujic Meho
Fatic Fata
Elephant Zebra
Bebic Beba
``````