Unit 6 of MAKAUT C Programming (PPS-II) covers composite data aggregation via structures (struct), unions, bitfields, pointer to structures, and structure memory alignment.

In MAKAUT semester exams, questions on Structure Memory Padding and full code implementations of a Student Database & Marksheet Grade System are mandatory items in Group C (15 Marks).

---

1. Introduction to User-Defined Data Types

While arrays are homogeneous (all elements of identical data type), a struct enables heterogeneous data aggregation under a unified name.

c
1struct Student {
2    int rollNo;
3    char name[50];
4    float marks;
5}; // Semicolon is mandatory!

---

2. Accessing Structure Members: . vs ->

  • Dot Operator (`.`): Used when accessing members via a structure variable (s1.rollNo).
  • Arrow Operator (`->`): Used when accessing members via a structure pointer (ptr->rollNo \equiv (*ptr).rollNo).

---

3. Structure Memory Alignment & Padding Explained

To optimize 32-bit/64-bit CPU word alignment, compilers insert unused padding bytes between structure fields.

c
1struct Example {
2    char c;    // 1 Byte
3    // 3 Bytes of Padding inserted here!
4    int i;     // 4 Bytes
5};

Size of struct Example equals 8 Bytes, not 5 Bytes!

To force exact packing without padding, use #pragma pack(1):

c
1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#pragma pack(1)
2struct PackedExample {
3    char c; // 1 Byte
4    int i;  // 4 Bytes
5}; // Total size = 5 Bytes

---

4. struct vs union Comparison

Feature`struct``union`
Memory AllocatedSum of sizes of all members + paddingSize of largest member only
Member AccessAll members accessible concurrentlyOnly one member accessible at a time
Keywordstructunion

---

5. Solved MAKAUT Exam Programs

Program 1: Student Information System (Nested Structures)

c
1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2 
3struct Address {
4    char city[30];
5    char state[30];
6    int pinCode;
7};
8 
9struct Student {
10    int rollNo;
11    char name[50];
12    struct Address addr; // Nested structure
13};
14 
15int main() {
16    struct Student s1 = {101, "Aritra Sen", {"Kolkata", "West Bengal", 700091}};
17 
18    printf("--- Student Profile ---\n");
19    printf("Roll No : %d\n", s1.rollNo);
20    printf("Name    : %s\n", s1.name);
21    printf("City    : %s\n", s1.addr.city);
22    printf("State   : %s\n", s1.addr.state);
23    printf("Pin Code: %d\n", s1.addr.pinCode);
24 
25    return 0;
26}

---

Program 2: MAKAUT Comprehensive Student Marksheet & Grade System

*Exam Context: Group C (15 Marks)*

c
1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2 
3"text-[#cf222e] dark:text-[#c586c0] font-semibold">#define MAX_SUBJECTS 5
4 
5struct Student {
6    int rollNo;
7    char name[50];
8    float marks[MAX_SUBJECTS];
9    float totalMarks;
10    float avgMarks;
11    char grade;
12};
13 
14char calculateGrade(float mark) {
15    if (mark >= 90) return 'O';
16    if (mark >= 80) return 'E';
17    if (mark >= 70) return 'A';
18    if (mark >= 60) return 'B';
19    if (mark >= 50) return 'C';
20    if (mark >= 40) return 'D';
21    return 'F';
22}
23 
24int main() {
25    int n = 2; // Student records count
26    struct Student students[2] = {
27        {101, "Rahul Banerjee", {85, 92, 78, 65, 88}},
28        {102, "Sneha Mukherjee", {95, 89, 91, 94, 90}}
29    };
30 
31    for (int i = 0; i < n; i++) {
32        students[i].totalMarks = 0;
33        for (int j = 0; j < MAX_SUBJECTS; j++) {
34            students[i].totalMarks += students[i].marks[j];
35        }
36        students[i].avgMarks = students[i].totalMarks / MAX_SUBJECTS;
37        students[i].grade = calculateGrade(students[i].avgMarks);
38    }
39 
40    printf("\n================ MAKAUT OFFICIAL MARKSHEET REPORT ================\n");
41    for (int i = 0; i < n; i++) {
42        printf("\nStudent Roll: %d | Name: %s\n", students[i].rollNo, students[i].name);
43        printf("------------------------------------------------------------------\n");
44        for (int j = 0; j < MAX_SUBJECTS; j++) {
45            printf("  Sub %d Mark: %5.2f | Sub Grade: %c\n", 
46                   j + 1, students[i].marks[j], calculateGrade(students[i].marks[j]));
47        }
48        printf("Total Marks : %.2f / 500.00\n", students[i].totalMarks);
49        printf("Average     : %.2f%%\n", students[i].avgMarks);
50        printf("Overall Totality Grade: %c\n", students[i].grade);
51    }
52    printf("==================================================================\n");
53 
54    return 0;
55}