Structures, unions, typedef

ACompressed recap

🧾

A struct bundles members of different types; reach them with . or, through a pointer, ->. Structs are copied on assignment and when passed; pass a pointer to modify. typedef renames types. A self-referential struct holds a pointer to its own type. Padding aligns each member to a multiple of its size and rounds the total to the largest member; reordering members can shrink a struct. A union overlays its members: size = largest member, rounded for alignment.

BMerged rule card

1.6 Structures, unions, typedef; self-referential structures; structure size and padding

• struct T { members }; access s.m or p->m ≡ (*p).m.
• Struct assignment and argument passing copy all members.
• typedef gives a type a new name.
• Self-referential: struct T { …; struct T *next; } (pointer only).
• Padding: member at multiple of its size; total multiple of largest member.
• union: members overlap; size = largest member rounded for alignment.

CInterleaved GATE-style questions

Q1NAT1 markPadding

Size of struct { char a; char b; int c; } (4-byte int, natural alignment)?

Numerical answer: ________

Q2NAT2 marksPadding

Size of struct { char a; int c; char b; } under the same rules?

Numerical answer: ________

Q3MCQ2 marksOutput

What does this print?

typedef struct {
    char name[8];
    int age;
} Person;

int main(void)
{
    Person team[2] = {{"Asha", 21}, {"Ravi", 23}};
    Person *p = team;
    p++;
    printf("%s %d %u\n", p->name, (p - 1)->age, sizeof(team));
    return 0;
}

• (A) Asha 23 24
• (B) Ravi 21 24
• (C) Ravi 23 24
• (D) Ravi 21 16

Q4MCQ1 markCopying

A function void f(struct point p) sets p.x = 0. After f(a), a.x is:

• (A) undefined
• (B) unchanged
• (C) a compile error
• (D) 0

Q5MCQ1 markUnion

A union with members double d; int i; char c; (8-byte double) has size:

• (A) 13
• (B) 16
• (C) 8
• (D) 4

Q6NAT2 marksPointer step

For struct item { char code; double price; short qty; } (natural alignment), how many bytes does p + 1 move a struct item *p?

Numerical answer: ________

Q7MSQ2 marksSyntax

With struct s { int v; struct s *n; } x, *p = &x;, which are valid expressions?

• (A) (*p).v
• (B) p->v
• (C) p->n->v (if p->n points to a struct s)
• (D) x->v

Q8MCQ2 marksOutput

What does this print?

struct link {
    int value;
    struct link *next;
};

int main(void)
{
    struct link c = {30, NULL};
    struct link b = {20, &c};
    struct link a = {10, &b};
    printf("%d %d %d\n", a.value, a.next->value, a.next->next->value);
    printf("%u\n", sizeof(struct link));
    return 0;
}

• (A) 10 10 10 then 8
• (B) 10 20 30 then 12
• (C) 30 20 10 then 8
• (D) 10 20 30 then 8

DAnswer Vault