Defining structures in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a structure in C++?

A structure in C++ is a user-defined data type that groups related variables of different types under one name. It helps organize data like a real-life object with multiple properties.

beginner

How do you define a simple structure named Person with name and age?

You define it like this:

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

beginner

How do you create a variable of a structure type and access its members?

First, declare a variable of the structure type, then use the dot . operator to access members.
Example:

Person p;
p.name = "Alice";
p.age = 30;

intermediate

Can structures in C++ have functions inside them?

Yes! Structures in C++ can have functions (called member functions) just like classes. This lets you group data and behavior together.

intermediate

What is the difference between a structure and a class in C++?

The main difference is default access:
- In a structure, members are public by default.
- In a class, members are private by default.
Otherwise, they are very similar.

How do you define a structure in C++?

A Using the keyword <code>class</code> only

B Using the keyword <code>function</code>

C Using the keyword <code>define</code>

D Using the keyword <code>struct</code> followed by the structure name and members

Structures are defined using the struct keyword followed by the name and member variables.

What operator is used to access members of a structure variable?

A Colon (:) operator

B Dot (.) operator

C Comma (,) operator

D Arrow (->) operator

The dot operator is used to access members of a structure variable.

What is the default access level of members in a C++ structure?

A Public

B Protected

C Private

D Package

Members of a structure are public by default.

Can a structure in C++ contain functions?

A Only if declared as <code>class</code>

B No, structures can only have variables

C Yes, structures can have member functions

D Only in C, not in C++

In C++, structures can have member functions just like classes.

Which of the following is a correct way to declare a structure variable?

A Both A and B

B struct Person p;

C Person p;

D None of the above

Both Person p; and struct Person p; are valid in C++.

Explain how to define a structure in C++ and create a variable of that structure.

Think about grouping related data under one name and how to use it.

Describe the differences and similarities between structures and classes in C++.

Focus on access and behavior.

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