Array of structures - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an array of 5 structures named 'students'.

C

struct Student {
    int id;
    char name[50];
};

struct Student [1];

Drag options to blanks, or click blank then click option'

Astudents[5]

Bstudents

CstudentArray

DstudentList[3]

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the array size.

Using a wrong variable name.

Declaring a single structure instead of an array.

The correct way to declare an array of 5 structures is to specify the array name followed by the size in square brackets.

2fill in blank

medium

Complete the code to access the 'id' of the third student in the array.

C

int third_id = students[1].id;

Drag options to blanks, or click blank then click option'

A.2

B[3]

C[2]

D->2

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 3 instead of 2.

Using dot or arrow operators incorrectly.

Array indices start at 0, so the third element is at index 2.

3fill in blank

hard

Fix the error in the code to assign the name "Alice" to the first student.

C

strcpy(students[1].name, "Alice");

Drag options to blanks, or click blank then click option'

A[1]

B.0

C->0

D[0]

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 1 instead of 0.

Using dot or arrow operators incorrectly.

The first element in the array is at index 0, so use students[0].

4fill in blank

hard

Fill both blanks to declare and initialize the second student's id to 102.

C

students[1].id [2] 102;

Drag options to blanks, or click blank then click option'

A[1]

B=

C==

D[0]

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '='.

Using the wrong index.

Use students[1] to access the second student and '=' to assign the value.

5fill in blank

hard

Fill all three blanks to print the name of the last student in the array.

C

printf("%s", students[1].[2]); // Array size is [3]

Drag options to blanks, or click blank then click option'

A[4]

Bname

C5

D[5]

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 5 which is out of bounds.

Using wrong field name.

Confusing array size with last index.

The last student in an array of size 5 is at index 4. The field to print is 'name'.

Practice

1. What is the correct way to declare an array of 5 structures named Student in C?

easy

A. Student arr[5];

B. struct Student arr;

C. Student arr;

D. struct arr[5];

Solution

1. Step 1: Understand structure array declaration

   To declare an array of structures, use the structure type followed by the array name and size in square brackets.

2. Step 2: Apply correct syntax for array of structures

   Since Student is the structure type, Student arr[5]; declares an array of 5 Student structures.

3. Final Answer:

   Student arr[5]; -> Option A

4. Quick Check:

   Array of structures = type name[size] [OK]

Hint: Use type name[size] to declare structure arrays [OK]

Common Mistakes:

• Forgetting 'struct' keyword if not typedefed
• Declaring single structure instead of array
• Using wrong syntax like struct arr[5];

2. Which of the following is the correct syntax to access the age member of the 3rd element in an array students of structures?

easy

A. students->age[3];

B. students.age[3];

C. students[3].age;

D. students[2].age;

Solution

1. Step 1: Understand zero-based indexing in arrays

   Arrays in C start at index 0, so the 3rd element is at index 2.

2. Step 2: Access structure member using dot operator

   Use students[2].age to access the age member of the 3rd element.

3. Final Answer:

   students[2].age; -> Option D

4. Quick Check:

   3rd element = index 2, use dot for member [OK]

Hint: Remember arrays start at 0; 3rd element is index 2 [OK]

Common Mistakes:

• Using index 3 instead of 2 for 3rd element
• Using arrow operator on array elements
• Accessing member as students.age[3]

3. Consider the code:

typedef struct {
  int id;
  char name[10];
} Item;

Item items[2] = {{1, "Pen"}, {2, "Book"}};

printf("%s", items[1].name);

What will be the output?

medium

A. Pen

B. Book

C. items[1].name

D. Compilation error

Solution

1. Step 1: Identify the array initialization

   The array items has two elements: first with id=1, name="Pen"; second with id=2, name="Book".

2. Step 2: Understand printf access

   items[1].name accesses the second element's name, which is "Book".

3. Final Answer:

   Book -> Option B

4. Quick Check:

   items[1].name = "Book" [OK]

Hint: Index 1 accesses second element's name [OK]

Common Mistakes:

• Confusing index 0 and 1
• Expecting id to print instead of name
• Syntax errors in initialization

4. What is wrong with this code snippet?

struct Point {
  int x, y;
};

struct Point points[3];
points[0].x = 10;
points[0].y = 20;
points[1].x = 30;
points[1].y = 40;
points[2].x = 50;
points[2].y = 60;

printf("%d", points[3].x);

medium

A. Array size should be 4 instead of 3

B. Missing semicolon after struct definition

C. Accessing points[3] is out of bounds

D. Incorrect struct member access syntax

Solution

1. Step 1: Check array size and indexing

   The array points has size 3, valid indices are 0, 1, 2.

2. Step 2: Identify invalid access

   Accessing points[3] is out of bounds and causes undefined behavior.

3. Final Answer:

   Accessing points[3] is out of bounds -> Option C

4. Quick Check:

   Array index must be less than size [OK]

Hint: Array indices go from 0 to size-1 only [OK]

Common Mistakes:

• Using index equal to array size
• Ignoring array bounds errors
• Assuming array auto-expands

5. You have a structure Employee with members int id; and float salary;. How do you write a function in C that takes an array of Employee and its size, then returns the average salary?

hard

A. float averageSalary(Employee emp[], int n) { float sum=0; for(int i=0;i

B. float averageSalary(Employee *emp, int n) { float sum=0; for(int i=0;isalary; return sum/n; }

C. float averageSalary(Employee emp[], int n) { float sum=0; for(int i=0;i

D. float averageSalary(Employee emp[], int n) { float sum=0; for(int i=0;i

Solution

1. Step 1: Loop through array elements correctly

   Use a for loop from 0 to n-1 and access each element with emp[i].

2. Step 2: Sum the salary member of each element

   Access salary as emp[i].salary and add to sum, then divide by n.

3. Final Answer:

   float averageSalary(Employee emp[], int n) { float sum=0; for(int i=0;i -> Option A

4. Quick Check:

   Loop + emp[i].salary sum / n = average [OK]

Hint: Use emp[i].member to access array struct members [OK]

Common Mistakes:

• Using emp->salary inside loop instead of emp[i].salary
• Accessing emp.salary instead of emp[i].salary
• Adding whole struct instead of member