Sorting array filled with lines of string - c

Question

I have a data in text like this:
1,jack,3,7.3
2,mike,4,8.6
3,gol,2,9
Could any one help me how to sort the data by the last column that represent the grades in descending using c language?
The question was posted before but with no code so I posted it again to get more help.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct
{
int cid;
char name[40];
char term[2];
double gpa;
}student;
typedef struct
{
char line[300];
}data;
typedef struct
{
int cid;
}finds;
typedef struct
{
double score;
}gpa;
void menu();
int calculateMax(void);
void addStudent();
void find();
void display();
void sort();
int main()
{
menu();
system("PAUSE");
return 0;
}
void menu()
{
int selection;
printf("%s", "Program menu :\n");
printf("%s", "1. Add a new student\n");
printf("%s", "2. Find/retrieve information for a particular Student\n");
printf("%s", "3. Display STUDENTS list\n");
printf("%s", "4. Find a student that has the lowest and the highest deposit\n");
printf("%s", "5. Quit\n");
printf("%s", "Selection : ");
scanf("%d", &selection);
if(selection == 1)
{
addStudent();
}
else if(selection == 2)
{
find();
}
else if(selection == 3)
{
display();
}
else if(selection == 4)
{
sort();
}
else if(selection == 5)
{
exit(0);
}
else {
printf("%s", "\n\aError, please key in correct input!\n\n");
menu();
}
}
void addStudent()
{
int max, i;
FILE *f, *id, *name, *term, *gpa , *sort;
printf("%s", "\n\nADD student\n");
printf("%s", "How many students you would like to add : ");
scanf("%d", &max);
student *student_info;
student_info = (student *) malloc(max * sizeof(student)); /*Allocate Memory For Client's Info*/
if(student_info == NULL)
{
printf("Unable to allocate space for client\n\n");
exit (EXIT_FAILURE);
}
if ((id = fopen("id.txt", "a+")) == NULL) /*Open file id.txt*/
{
printf("Error, the file cannot be opened\n");
}
if ((name = fopen("name.txt", "a+")) == NULL) /*Open file name.txt*/
{
printf("Error, the file cannot be opened\n");
}
if ((term = fopen("term.txt", "a+")) == NULL) /*Open file TERM.txt*/
{
printf("Error, the file cannot be opened\n");
}
if ((gpa = fopen("gpa.txt", "a+")) == NULL) /*Open file GPA.txt*/
{
printf("Error, the file cannot be opened\n");
}
if ((f = fopen("student.txt", "a+")) == NULL) /*Open file STUDENTS.txt*/
{
printf("Error, the file cannot be opened\n");
}
if ((sort = fopen("sort.txt", "a+")) == NULL) /*Open file SORT.txt*/
{
printf("Error, the file cannot be opened\n");
}
else {
for (i = 0; i < max ; i++) { /*Get the input data*/
printf("student %d\n", i + 1);
printf("%s", "student's Id : ");
scanf("%5d", &student_info[i].cid);
printf("%s", "student's Name : ");
fflush(stdin);
gets(student_info[i].name);
printf("%s", "student's term : ");
fflush(stdin);
gets(student_info[i].term);
printf("%s", "student's GPA : ");
scanf("%7lf", &student_info[i].gpa);
printf("\n");
}
}
for(i = 0; i < max; i++) { /*Store input data into files*/
fprintf(id, "%d\n", student_info[i].cid);
fputs(student_info[i].name, name);
fprintf(name, "\n");
fputs(student_info[i].term, term);
fprintf(term, "\n");
fprintf(gpa, "%lf\n", student_info[i].gpa);
fprintf(sort,"%d,%s,%s,%lf\n",student_info[i].cid,student_info[i].name,student_info[i].term,student_info[i].gpa);
}
for(i = 0; i < max; i++) {
fprintf(f, "%d", student_info[i].cid, "");
fprintf(f, "%3s", "");
fputs(student_info[i].name, f);
fprintf(f, "%5s", "");
fputs(student_info[i].term, f);
fprintf(f, "%7s", "");
fprintf(f, "%lf\n", student_info[i].gpa);
}
fclose(f);
fclose(id);
fclose(name);
fclose(term);
fclose(gpa);
fclose(sort);
free(student_info);
student_info = NULL;
printf("\n");
menu();
}
void find()
{
int find_id = 0, i = 0, student_cid, n = 0, max, selection;
FILE *id, *f;
max = calculateMax();
finds *result;
result = (finds *) malloc(max * sizeof(finds));
if(result == NULL)
{
printf("Unable to allocate space for student\n\n");
exit (EXIT_FAILURE);
}
if ((id = fopen("id.txt", "r")) == NULL)
{
printf("Error, the file cannot be opened\n");
}
else {
while (!feof(id)) { /*Get all clients' id number and store to array*/
fscanf(id, "%d", &result[i].cid);
i++;
}
}
fclose(id);
printf("%s", "\n\nFIND STUDENT\n");
printf("%s", "Key in Student's id : "); /*Get the client's id that user want to query*/
scanf("%d", &student_cid);
data *student_info;
student_info = (data *) malloc(max * sizeof(data));
if(student_info == NULL)
{
printf("Unable to allocate space for student\n\n");
exit (EXIT_FAILURE);
}
if ((f = fopen("student.txt", "r")) == NULL)
{
printf("Error, the file cannot be opened\n");
}
i = 0;
while (!feof(f)) { /*Get all the students' data from clients.txt and stored to array*/
fflush(stdin);
fgets(student_info[i].line, 300, f);
i++;
}
fclose (f);
for(i = 0; i < max + 1; i++)
{
if(student_cid == result[i].cid)
{
printf("\n\n%s%6s%20s%17s\n", "ID", "NAME", "TERM", "GPA");
puts(student_info[i].line);
free(student_info);
student_info = NULL;
free(result);
result = NULL;
printf("Would you like to find another student?\nKey in 1 for yes or 2 to go to menu : ");
scanf("%d",&selection);
if(selection == 1) {
find();
}
else if(selection == 2) {
menu();
}
break;
}
else if(i == max)
{
printf("\nSory, there's no student with that exist in database.\n");
free(student_info);
student_info = NULL;
free(result);
result = NULL;
printf("Would you like to find another student?\nKey in 1 for yes or 2 to go to menu : ");
scanf("%d",&selection);
if(selection == 1) {
find();
}
else if(selection == 2) {
printf("\n\n");
menu();
}
}
}
}
void display()
{
int max = 0, i;
FILE *f;
printf("\n\nDISPLAY STUDENT");
max = calculateMax();
data *student_info;
student_info = (data *) malloc(max * sizeof(data));
if(student_info == NULL)
{
printf("Unable to allocate space for student\n\n");
exit (EXIT_FAILURE);
}
if ((f = fopen("student.txt", "r")) == NULL)
{
printf("Error, the file cannot be opened\n");
}
i = 0;
while (!feof(f)) {
fflush(stdin);
fgets(student_info[i].line, 200, f);
i++;
}
fclose (f);
printf("\n\n%s%6s%20s%17s\n", "ID", "NAME", "TERM", "GPA");
for(i = 0; i < max; i++)
{
puts(student_info[i].line);
}
free(student_info);
student_info = NULL;
}
int calculateMax(void)
{
char str[150];
int maximum = 0;
FILE *f;
if ((f = fopen("student.txt", "r")) == NULL)
{
printf("Error, the file cannot be opened\n");
}
else {
while (!feof(f)) {
maximum++;
fgets (str , 200 , f);
}
}
fclose (f);
maximum = maximum - 1;
return maximum;
}
////////////////////////////////////////////////////////////////////
static int student_info_compare(const void *a, const void *b)
{
const student_info *sia = a, *sib = b;
return strcmp(sia->name, sib->name);
}
void Sortdisplay()
{
int max = 0, i;
FILE *f;
printf("\n\nDISPLAY SORTED STUDENT");
max = calculateMax();
data *student_info;
student_info = (data *) malloc(max * sizeof(data));
if(student_info == NULL)
{
printf("Unable to allocate space for student\n\n");
exit (EXIT_FAILURE);
}
if ((f = fopen("sort.txt", "r")) == NULL)
{
printf("Error, the file cannot be opened\n");
}
i = 0;
while (!feof(f)) {
fflush(stdin);
fgets(student_info[i].line, 200, f);
i++;
}
fclose (f);
printf("\n\n%s%6s%20s%17s\n", "ID", "NAME", "TERM", "GPA");
student_info_compare();
for(i = 0; i < max; i++)
{
// iwant to sort here
qsort(student_info, max, sizeof student_info[0], student_info_compare);
puts(student_info[i].line);
}
free(student_info);
student_info = NULL;
}

Answer 1

Try this:
static int student_info_compare(const void *a, const void *b)
{
const student_info *sia = a, *sib = b;
return strcmp(sia->name, sib->name);
}
then add this before the print loop:
qsort(student_info, max, sizeof student_info[0], student_info_compare);
This uses the standard qsort() function to sort the array. The student_info_compare() function serves as the comparison-callback, since qsort() doesn't know how your data looks.
The arguments to the comparison-callback have type const void *, which basically means "here's a pointer to something whose exact type is not known, and you're supposed to treat it as a read-only pointer". That's how qsort() passes pointers to the array elements, since (again) it doesn't know that they are of type const student_info *.