Insertion code using file stream - c

Question

Here is the task i'm working on:
I am given a txt file containing the list of student names, id numbers, schools, majors, and test scores.
Read this contents and copy to the structure in C.
Sort this list using insertion sort.
Print sorted list on the screen.
I checked my coding by muting some parts, there is an error with my insertion sorting function.
I have no idea which part is incorrect. It all makes sense to me. I need help :( here is the code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX 1000
#define BUF_SIZE 80
typedef struct {
char name[20];
char studentID[10];
char department[20];
char major[20];
int mid;
int final;
} student;
FILE *fp;
void operation(student t, student list[], int j);
void insertion_sort(student list[], int n);
void printing(student list[], int n);
int main(int argc, char *argv[])
{
char filename[20] = "studentlist.txt";
int n = 1; /* (number of students) + 1 */
student list[MAX];
char buffer[BUF_SIZE];
int i;
fp = fopen(filename, "r");
while (1) {
if (fgets(buffer, BUF_SIZE, fp) == NULL)
break;
strncpy(list[n].name, buffer, strlen(buffer) - 1);
fgets(buffer, BUF_SIZE, fp);
strncpy(list[n].studentID, buffer, strlen(buffer) - 1);
fgets(buffer, BUF_SIZE, fp);
strncpy(list[n].department, buffer, strlen(buffer) - 1);
fgets(buffer, BUF_SIZE, fp);
strncpy(list[n].major, buffer, strlen(buffer) - 1);
fgets(buffer, BUF_SIZE, fp);
list[n].mid = atoi(buffer);
fgets(buffer, BUF_SIZE, fp);
list[n].final = atoi(buffer);
n++;
}
fclose(fp);
insertion_sort(list, n);
printing(list, n);
return 0;
}
void insertion_sort(student list[], int n)
{
int i;
student temp;
for (i = 2; i < n; i++) {
temp = list[i];
operation(temp, list, i - 1);
}
}
void operation(student t, student list[], int j)
{
list[0] = t;
while (t.studentID < list[j].studentID) {
list[j + 1] = list[j];
j--;
}
list[j + 1] = t;
}
void printing(student list[], int n)
{
int i;
for (i = 1; i < n; i++) {
printf(" %s ", list[i].name);
printf(" %s ", list[i].studentID);
printf(" %s ", list[i].department);
printf(" %s ", list[i].major);
printf(" %6d ", list[i].mid);
printf(" %6d ", list[i].final);
putchar('\n');
}
}

Answer 1

Continuing from the comments and the first answer, you are making tracking index error between the split insertion_sort and operation functions. There is no need for two functions when one will work (and arguably be smaller). There is little benefit to be obtained from the split (except for increased confusion).
Putting a simple insertion sort together in one function that will fit your needs (and using pointers to sort as opposed to repeatedly using the function copy-constructor to accomplish the swaps), you could do something similar to the following:
typedef struct {
int id, g;
} student;
void insertion_sort (student **list, int nmemb)
{
for (int i = 0; i < nmemb; i++)
for (int j = i; j > 0 && list[j]->id < list[j-1]->id; j--)
{
student *tmp = list[j];
list[j] = list[j-1];
list[j-1] = tmp;
}
}
Putting together a short (and limited struct member example), you can do something like the following to sort the student data by ID (or id below)
#include <stdio.h>
typedef struct {
int id, g;
} student;
void insertion_sort (student **list, int nmemb)
{
for (int i = 0; i < nmemb; i++)
for (int j = i; j > 0 && list[j]->id < list[j-1]->id; j--)
{
student *tmp = list[j];
list[j] = list[j-1];
list[j-1] = tmp;
}
}
void printing(student *list[], int n)
{
int i;
for (i = 0; i < n; i++) {
printf(" %d ", list[i]->id);
printf(" %d \n", list[i]->g);
}
}
int main (void) {
student s[] = { {.id = 5, .g = 72}, /* minimal student test data */
{.id = 2, .g = 91},
{.id = 4, .g = 77},
{.id = 1, .g = 96},
{.id = 3, .g = 85}};
int n = sizeof s / sizeof *s;
student *l[n];
for (int i = 0; i < n; i++) /* initialize pointers in l */
l[i] = &s[i];
insertion_sort (l, n); /* sort pointers in l */
printing (l, n); /* output sorted pointers */
return 0;
}
Example Use/Output
Sorted by student.id
$ ./bin/inssort_so
1 96
2 91
3 85
4 77
5 72
If you did want to avoid using the additional level of indirection involved in passing an array of pointers (actually a pointer-to-pointer-to-type), you can make your original approach work as follows:
void insertion_sort (student *list, int nmemb)
{
for (int i = 0; i < nmemb; i++)
for (int j = i; j > 0 && list[j].id < list[j-1].id; j--)
{
student tmp = list[j];
list[j] = list[j-1];
list[j-1] = tmp;
}
}
void printing (student *list, int n)
{
for (int i = 0; i < n; i++)
printf (" %d %d \n", list[i].id, list[i].g);
}
int main (void) {
student s[] = { {.id = 5, .g = 72},
{.id = 2, .g = 91},
{.id = 4, .g = 77},
{.id = 1, .g = 96},
{.id = 3, .g = 85}};
int n = sizeof s / sizeof *s;
insertion_sort (s, n);
printing (s, n);
return 0;
}
As you go forward, also consider passing a compare callback function to your sort routines. That allows you to sort many different types of data using your same sort routine -- just by changing the compare function (as is done for the C-library qsort routine.