Accessing structure members - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of accessing structure members with pointers

What is the output of this C code snippet?

C

#include <stdio.h>

struct Point {
    int x;
    int y;
};

int main() {
    struct Point p = {3, 4};
    struct Point *ptr = &p;
    printf("%d %d\n", ptr->x, (*ptr).y);
    return 0;
}

A 3 4

B 4 3

C 0 0

D Compilation error

💡 Hint

Remember that '->' accesses members through a pointer, and '(*ptr).member' is equivalent.

The pointer 'ptr' points to 'p'. Accessing 'ptr->x' gives 3 and '(*ptr).y' gives 4, so output is '3 4'.

❓ Predict Output

intermediate

Output when accessing nested structure members

What will this program print?

C

#include <stdio.h>

struct Date {
    int day;
    int month;
    int year;
};

struct Event {
    char name[20];
    struct Date date;
};

int main() {
    struct Event e = {"Meeting", {15, 8, 2024}};
    printf("%d/%d/%d\n", e.date.day, e.date.month, e.date.year);
    return 0;
}

A Compilation error

B 15/8/2024

C 2024/8/15

D 8/15/2024

💡 Hint

Check the order of members in the nested structure.

The 'date' member of 'e' is initialized with day=15, month=8, year=2024. So the output is '15/8/2024'.

🔧 Debug

advanced

Identify the error in accessing structure members

What error does this code produce when compiled?

C

#include <stdio.h>

struct Person {
    char name[10];
    int age;
};

int main() {
    struct Person p = {"Alice", 30};
    struct Person *ptr = &p;
    printf("Name: %s, Age: %d\n", *ptr->name, ptr->age);
    return 0;
}

A Compilation error: invalid operands to binary ->

B Output: Name: Alice, Age: 30

C Runtime error: segmentation fault

D Compilation error: invalid type argument of unary '*'

💡 Hint

Look carefully at the expression '*ptr->name' and operator precedence.

The expression '*ptr->name' tries to dereference a char array which is invalid here. The correct way is 'ptr->name' without '*'.

❓ Predict Output

advanced

Output of structure member modification via pointer

What is the output of this program?

C

#include <stdio.h>

struct Counter {
    int count;
};

int main() {
    struct Counter c = {10};
    struct Counter *p = &c;
    p->count += 5;
    (*p).count += 10;
    printf("%d\n", c.count);
    return 0;
}

A 25

B 15

C 10

D Compilation error

💡 Hint

Both 'p->count' and '(*p).count' modify the same member.

Starting from 10, adding 5 then 10 results in 25 printed.

🧠 Conceptual

expert

Number of items in an array of structures after pointer manipulation

Given the code below, how many elements does the array 'arr' have, and what is the value of 'ptr[2].value'?

C

#include <stdio.h>

struct Item {
    int value;
};

int main() {
    struct Item arr[4] = {{1}, {2}, {3}, {4}};
    struct Item *ptr = arr;
    ptr++;
    printf("%d\n", ptr[2].value);
    return 0;
}

A Array has 4 elements; output is 3

B Array has 3 elements; output is 3

C Array has 4 elements; output is 4

D Array has 3 elements; output is 4

💡 Hint

Pointer arithmetic moves the pointer; indexing is relative to the new pointer position.

The array 'arr' has 4 elements. After 'ptr++', 'ptr' points to arr[1]. So 'ptr[2]' is arr[3], which has value 4.