Defining structures in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of structure member access

What is the output of this C++ code?

C++

struct Point {
    int x;
    int y;
};

int main() {
    Point p = {3, 4};
    std::cout << p.x + p.y << std::endl;
    return 0;
}

A 7

B 34

C 0

D Compilation error

💡 Hint

Add the values of x and y members of the structure.

The structure Point has members x=3 and y=4. Adding them gives 7.

❓ Predict Output

intermediate

Size of structure with padding

What is the size of this structure on a typical 64-bit system?

C++

struct Data {
    char a;
    int b;
    char c;
};

int main() {
    std::cout << sizeof(Data) << std::endl;
    return 0;
}

A 8

B 6

C 12

D 16

💡 Hint

Consider padding added for alignment between members.

The compiler adds padding to align int on 4 bytes. The total size becomes 12 bytes.

🔧 Debug

advanced

Identify the error in structure initialization

What error will this code produce?

C++

#include <iostream>
#include <string>

struct Person {
    std::string name;
    int age;
};

int main() {
    Person p = {"Alice"};
    std::cout << p.name << " " << p.age << std::endl;
    return 0;
}

A Compilation error: missing initializer for 'age'

B Runtime error: uninitialized age

C Output: Alice 0

D Output: Alice garbage_value

💡 Hint

All members must be initialized or have default values.

The code misses initializing 'age', causing a compilation error in strict initialization.

🧠 Conceptual

advanced

Effect of 'typedef' with structures

What does the following code do?

C++

#include <iostream>

typedef struct {
    int id;
    float score;
} Record;

int main() {
    Record r = {101, 95.5};
    std::cout << r.id << " " << r.score << std::endl;
    return 0;
}

A Defines a structure named 'Record' and a variable of that type

B Defines a structure and creates an alias 'Record' for it

C Causes a syntax error due to missing structure name

D Defines a class named 'Record' instead of a structure

💡 Hint

typedef creates a new name for the unnamed structure.

The typedef creates an alias 'Record' for the unnamed struct, allowing easy use.

❓ Predict Output

expert

Output of nested structure member access

What is the output of this code?

C++

struct Engine {
    int horsepower;
};

struct Car {
    Engine engine;
    int year;
};

int main() {
    Car c = {{250}, 2020};
    std::cout << c.engine.horsepower << " " << c.year << std::endl;
    return 0;
}

A 250 0

B Compilation error

C 0 2020

D 250 2020

💡 Hint

Nested structures can be initialized with nested braces.

The nested structure Engine is initialized with 250 horsepower, and year is 2020.

Practice

1. What is the purpose of a struct in C++?

easy

A. To group related variables under one name

B. To create a loop structure

C. To define a function

D. To allocate memory dynamically

Solution

1. Step 1: Understand the role of struct

   A struct is used to group different variables together under one name, making it easier to manage related data.

2. Step 2: Compare with other options

   Options A, C, and D describe loops, functions, and memory allocation, which are unrelated to struct.

3. Final Answer:

   To group related variables under one name -> Option A

4. Quick Check:

   Struct groups data = B [OK]

Hint: Remember: struct bundles variables like a box [OK]

Common Mistakes:

• Confusing struct with functions
• Thinking struct creates loops
• Mixing struct with dynamic memory

2. Which of the following is the correct way to define a structure named Person with members name (string) and age (int)?

easy

A. struct Person = { string name; int age; };

B. struct Person ( string name; int age; );

C. struct Person { string name; int age; };

D. struct Person: string name; int age;

Solution

1. Step 1: Recall correct struct syntax

   In C++, a struct is defined using curly braces { } with members inside, ending with a semicolon.

2. Step 2: Check each option

   struct Person { string name; int age; }; uses correct syntax with braces and semicolon. Options B, C, and D use incorrect symbols or missing braces.

3. Final Answer:

   struct Person { string name; int age; }; -> Option C

4. Quick Check:

   Struct uses braces and semicolon = A [OK]

Hint: Use braces { } and end with semicolon ; [OK]

Common Mistakes:

• Using parentheses instead of braces
• Omitting the semicolon after struct
• Using equal sign or colon wrongly

3. What will be the output of this code?

struct Point { int x; int y; };
int main() {
  Point p = {3, 4};
  std::cout << p.x << "," << p.y << std::endl;
  return 0;
}

medium

A. 3,4

B. 4,3

C. x,y

D. Compilation error

Solution

1. Step 1: Understand struct initialization

   The struct Point is initialized with {3, 4}, so p.x = 3 and p.y = 4.

2. Step 2: Check output statement

   The code prints p.x then a comma, then p.y, so output is "3,4".

3. Final Answer:

   3,4 -> Option A

4. Quick Check:

   p.x=3 and p.y=4 prints 3,4 [OK]

Hint: Struct members print in order assigned [OK]

Common Mistakes:

• Swapping member values
• Expecting member names to print
• Thinking initialization causes error

4. Identify the error in this structure definition:

struct Car {
  string model
  int year;
};

medium

A. Cannot have string type in struct

B. Missing semicolon after Car struct

C. Wrong keyword used instead of struct

D. Missing semicolon after model member

Solution

1. Step 1: Check member declarations

   Each member must end with a semicolon. The model member is missing a semicolon.

2. Step 2: Verify struct ending

   The struct ends with a semicolon, which is correct. The keyword struct is correct. String type is allowed.

3. Final Answer:

   Missing semicolon after model member -> Option D

4. Quick Check:

   Each member needs ; = A [OK]

Hint: Check each member line ends with ; [OK]

Common Mistakes:

• Forgetting semicolon after members
• Confusing struct end semicolon with member semicolon
• Thinking string is invalid type

5. Given the structure:

struct Employee {
  string name;
  int id;
  double salary;
};

Which code correctly creates an Employee variable and sets the salary to 50000.0?

hard

A. Employee e; e.salary = 50000.0;

B. All of the above

C. Employee e = {"John", 101, 50000.0};

D. Employee e = {"John", 101}; e.salary = 50000.0;

Solution

1. Step 1: Check each option for valid struct usage

   Employee e; e.salary = 50000.0; creates an Employee and sets salary directly, which is valid.

2. Step 2: Analyze options B and C

   Employee e = {"John", 101}; e.salary = 50000.0; initializes name and id, then sets salary separately, valid. Employee e = {"John", 101, 50000.0}; initializes all members at once, also valid.

3. Step 3: Confirm all options are correct

   All three ways correctly create and set salary.

4. Final Answer:

   All of the above -> Option B

5. Quick Check:

   Multiple valid ways to set struct members = D [OK]

Hint: Struct members can be set during or after creation [OK]

Common Mistakes:

• Thinking partial initialization is invalid
• Assuming only one correct way to assign members
• Forgetting to set salary after partial init