Quick Sort in C

Use the following structure definition to answer question 

struct subject { 

char subjectID[10]; 

float marks; 

}; 

struct student { 

char name[20]; 

char ID[10]; 

struct subject *enrolled; 

}; 

Write a C program to fulfil the following Menu requirements 

a. Add Student - Your program should allow creation of any number of students. Each student must enrol in at least one subject and maximum of 4 subjects. 

b. Display Students – Display the details of all the students along with their subject details 

c. Rank Students – Display students based on the Average marks. Student with the highest average marks to be displayed first  

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

#define MAX_SUBJECTS 4
#define MAX_MARKS 100

typedef struct subject {
    char subjectID[10];
    float marks;
}subject_db_t;

typedef struct student {
    char name[20];
    char ID[10];
    struct subject *enrolled;
}student_db_t;

void allocate_student_memory(student_db_t *stud, int index, int *stud_sub)
{
    int sub_index = 0;
    char tmp_subj_name[20] = {0};
    float tmp_marks = 0;

    // Allocate memory for each student's subject
    stud[index].enrolled = (subject_db_t *)malloc(stud_sub[index] * sizeof(subject_db_t));
    for (sub_index = 0; sub_index < stud_sub[index]; sub_index++) {
        printf("Student[%s] Subject[%d] Name\t", stud[index].ID, sub_index + 1);
        scanf("%s", tmp_subj_name);
        strncpy(stud[index].enrolled[sub_index].subjectID, tmp_subj_name,
                strlen(tmp_subj_name));
        printf("\n");

        printf("Student[%s] Subject[%d] Mark \t", stud[index].ID, sub_index + 1);
        scanf("%f", &tmp_marks);
        stud[index].enrolled[sub_index].marks = tmp_marks;
        printf("\n");
    }
}

void Free_student(student_db_t *stud, int no_stud)
{
    int index = 0;
    for (index = 0; index < no_stud; index++)
        free(stud[index].enrolled);
}

void Display_sorted_student(student_db_t *stud, int no_stud, int *average_mark, int *stud_sub)
{
    int in = 0, index = 0, sub_index = 0;

    printf("Index - Stud ID  -  Name -   Sub1   - Mark -   Sub2   - Mark -   Sub3   - Mark -"
           "   Sub4   - Mark - Avg_Mark\n");
    printf("-------------------------------------------------------------------------"
           "-----------------------------------\n");
    for (index = 0; index < no_stud; index++) {
        printf("%5d   %7s  ", index + 1, stud[index].ID);
        printf("%8s ", stud[index].name);
        for (sub_index = 0; sub_index < stud_sub[index]; sub_index++) {
            printf("%8.4s  ", stud[index].enrolled[sub_index].subjectID);
            printf("%6.2f  ", stud[index].enrolled[sub_index].marks);
        }
        // Not enrolled subject details will be displayed as "-"
        if (stud_sub[index] < MAX_SUBJECTS) {
            for (in = stud_sub[index]; in < MAX_SUBJECTS; in++) {
                printf("     -        -   ");
            }
        }
        printf("  %d\n", average_mark[index]);
    }
    printf("\n");
}

void Display_student(student_db_t *stud, int no_stud, int *average_mark, int *stud_sub)
{
    int in = 0, index = 0, sub_index = 0;
    int total_marks = 0;

    printf("Index - Stud ID  -  Name -   Sub1   - Mark -   Sub2   - Mark -   Sub3   - Mark -"
           "   Sub4   - Mark - Avg_Mark\n");
    printf("-------------------------------------------------------------------------"
           "-----------------------------------\n");
    for (index = 0; index < no_stud; index++) {
        printf("%5d   %7s  ", index + 1, stud[index].ID);
        printf("%8s ", stud[index].name);
        total_marks = 0;
        for (sub_index = 0; sub_index < stud_sub[index]; sub_index++) {
            printf("%8.4s  ", stud[index].enrolled[sub_index].subjectID);
            printf("%6.2f  ", stud[index].enrolled[sub_index].marks);
            total_marks += stud[index].enrolled[sub_index].marks;
        }
        // Not enrolled subject details will be displayed as "-"
        if (stud_sub[index] < MAX_SUBJECTS) {
            for (in = stud_sub[index]; in < MAX_SUBJECTS; in++) {
                printf("     -        -   ");
            }
        }
        average_mark[index] = total_marks / stud_sub[index];
        printf("  %d\n", average_mark[index]);
    }
    printf("\n");
}

void swap(int *left, int * right)
{
    int tmp = *right;
    *right = *left;
    *left = tmp;
    return;
}

void swap_student(student_db_t *left_stud, student_db_t *right_stud)
{
    student_db_t tmp_stud = *right_stud;
    *right_stud = *left_stud;
    *left_stud = tmp_stud;
    return;
}

int partition(int *avg_mark, int *stud_sub, student_db_t *stud, int low, int high)
{
    int pivot = avg_mark[high];
    int index = 0;
    int start = low - 1;

    for (index = low; index < high; index++) {
        // Keep all elements greater than pivot at its left
        if (avg_mark[index] >= pivot) {
            start++;
            swap(&avg_mark[start], &avg_mark[index]);
            swap(&stud_sub[start], &stud_sub[index]);
            swap_student(&stud[start], &stud[index]);
        }
    }

    // Place pivot at its proper place
    swap(&avg_mark[start + 1], &avg_mark[high]);
    swap(&stud_sub[start + 1], &stud_sub[high]);
    swap_student(&stud[start + 1], &stud[high]);
    return (start + 1);
}

void sort_student_on_rank(int *avg_mark, int *stud_sub,
                          student_db_t *stud, int low, int high)
{
    int index = 0;

    if (low < high) {
        index = partition(avg_mark, stud_sub, stud, low, high);
        // After partition sort the pivot left and right elements
        sort_student_on_rank(avg_mark, stud_sub, stud, low, index -1);
        sort_student_on_rank(avg_mark, stud_sub, stud, index + 1, high);
    }
    return;
}

void Rank_student(int *avg_mark, int *stud_sub, student_db_t *stud,
                  int low, int high)
{
    int index;
    sort_student_on_rank(avg_mark, stud_sub, stud, low, high);
    return;
}

int main()
{
    int no_stud = 0;
    int in = 0, index = 0, sub_index = 0;
    char tmp_subj_name[20] = {0};
    float tmp_marks = 0;
    int total_marks = 0;

    printf("Enter number of students\t");
    scanf("%d", &no_stud);

    student_db_t stud[no_stud];
    int stud_sub[no_stud];
    int average_mark[no_stud];

    // Add Student
    for (; index < no_stud; index++) {
        printf("Enter student %d Name\t", index + 1);
        scanf("%s", stud[index].name);
        printf("\n");

        printf("Enter student %d Roll Number\t", index + 1);
        scanf("%s", stud[index].ID);
        printf("\n");

        printf("Enter the number of subjects\t");
        scanf("%d", &stud_sub[index]);

        if (stud_sub[index] > MAX_SUBJECTS) {
            printf("You've entered more than maximum. Subjects can be enrolled"
                    "upto maximum %d\n", MAX_SUBJECTS);
            printf("Re-enter number of subjects\t");
            scanf("%d", &stud_sub[index]);
        }
        // Allocate Memory based on the subjects enrolled for
        allocate_student_memory(stud, index, stud_sub);
    }

    // Display Students with their subject details
    Display_student(stud, no_stud, average_mark, stud_sub);
    // Rank Students
    Rank_student(average_mark, stud_sub, stud, 0, no_stud - 1);
    // Display Students based on rank
    Display_sorted_student(stud, no_stud, average_mark, stud_sub);
    // Free the Students
    Free_student(stud, no_stud);

    return 0;
}

Output:

Enter number of students        4 Enter student 1 Name    Shirley Enter student 1 Roll Number     07IT073 Enter the number of subjects    3 Student[07IT073] Subject[1] Name        Tamil Student[07IT073] Subject[1] Mark        45 Student[07IT073] Subject[2] Name        English Student[07IT073] Subject[2] Mark        67 Student[07IT073] Subject[3] Name        Mathematics Student[07IT073] Subject[3] Mark        55 Enter student 2 Name    Vicky Enter student 2 Roll Number     06IT089 Enter the number of subjects    4 Student[06IT089] Subject[1] Name        Hindhi Student[06IT089] Subject[1] Mark        79 Student[06IT089] Subject[2] Name        English Student[06IT089] Subject[2] Mark        85 Student[06IT089] Subject[3] Name        ComputerScience Student[06IT089] Subject[3] Mark        90 Student[06IT089] Subject[4] Name        Physics Student[06IT089] Subject[4] Mark        77 Enter student 3 Name    Sivy Enter student 3 Roll Number     06IT090 Enter the number of subjects    2 Student[06IT090] Subject[1] Name        Chemistry Student[06IT090] Subject[1] Mark        80 Student[06IT090] Subject[2] Name        English Student[06IT090] Subject[2] Mark        57 Enter student 4 Name    Sweety Enter student 4 Roll Number     07IT090 Enter the number of subjects    1 Student[07IT090] Subject[1] Name        Chemistry Student[07IT090] Subject[1] Mark        65  Index - Stud ID  -  Name -   Sub1   - Mark -   Sub2   - Mark -   Sub3   - Mark -   Sub4   - Mark - Avg_Mark ------------------------------------------------------------------------------------------------------------     1   07IT073   Shirley     Tami   45.00      Engl   67.00      Math   55.00       -        -     55     2   06IT089     Vicky     Hind   79.00      Engl   85.00      Comp   90.00      Phys   77.00    82     3   06IT090      Sivy     Chem   80.00      Engl   57.00       -        -        -        -     68     4   07IT090    Sweety     Chem   65.00       -        -        -        -        -        -     65   Index - Stud ID  -  Name -   Sub1   - Mark -   Sub2   - Mark -   Sub3   - Mark -   Sub4   - Mark - Avg_Mark ------------------------------------------------------------------------------------------------------------     1   06IT089     Vicky     Hind   79.00      Engl   85.00      Comp   90.00      Phys   77.00    82     2   06IT090      Sivy     Chem   80.00      Engl   57.00       -        -        -        -     68     3   07IT090    Sweety     Chem   65.00       -        -        -        -        -        -     65     4   07IT073   Shirley     Tami   45.00      Engl   67.00      Math   55.00       -        -     55