C++: Struct Basics

Last updated: 2026-08-26

Arrays can store multiple values of the same type, but what if you need to store a student's name (string), age (integer), score (floating-point)?

That's where structs come in — combining multiple variables of different types into a single unit.

1. What Is a Struct?

(1) 1.1 Structs in Everyday Life

Real-Life Example	Program Equivalent
A business card (name, phone, email)	Struct
A book (title, author, price)	Struct
A student (name, age, score)	Struct

Characteristics of Structs:

Members can have different types
Contiguous memory (like arrays)
A precursor to "classes" (you'll learn classes later)

(2) 1.2 Why Do We Need Structs?

Without structs (tedious):

▶ Example 2: Code Example (Difficulty ⭐)

CPP

#include <iostream>
#include <string>

int main() {
 std::string name1 = "Alice";
 int age1 = 20;
 double score1 = 92.5;
 
 std::string name2 = "Bob";
 int age2 = 21;
 double score2 = 88.0;
 // ... you'd need to declare 3 × 100 variables!
 
 return 0;
}

▶ Try it Yourself

Output:

TEXT 📖 Display only

(program output)

With structs (concise):

CPP

#include <iostream>
#include <string>

struct Student {
 std::string name;
 int age;
 double score;
};

int main() {
 Student s1 = {"Alice", 20, 92.5};
 Student s2 = {"Bob", 21, 88.0};
 // ... much cleaner!
 
 return 0;
}

2. Declaring and Defining Structs

(1) 2.1 Declaring a Struct

Syntax:

TEXT 📖 Display only

struct StructName {
 memberType1 memberName1;
 memberType2 memberName2;
 ...
};

Example:

CPP

#include <iostream>
#include <string>

// Declare a struct
struct Student {
 std::string name;
 int age;
 double score;
}; // ⚠️ Note: the semicolon is required!

int main() {
 // ...
 return 0;
}

💡 Key Point: A struct declaration ends with a semicolon! This is a common mistake for beginners.

3. Creating and Initializing Struct Variables

(1) 3.1 Creating a Struct Variable

CPP

Student s1; // Create a variable s1 of type Student

(2) 3.2 Initializing a Struct Variable

Method 1: Initialize in declaration order

TEXT 📖 Display only

Student s1 = {"Alice", 20, 92.5};

Method 2: Designated member initialization (C++20, recommended)

CPP

Student s1 = {.name = "Alice", .age = 20, .score = 92.5};

Method 3: Assign values individually

TEXT 📖 Display only

Student s1;
s1.name = "Alice";
s1.age = 20;
s1.score = 92.5;

💡 Tip: Method 1 or Method 2 is recommended for conciseness.

4. Accessing Struct Members

(1) 4.1 Reading Members

Syntax:

TEXT 📖 Display only

structName.memberName

Example:

CPP

#include <iostream>
#include <string>

struct Student {
 std::string name;
 int age;
 double score;
};

int main() {
 Student s1 = {"Alice", 20, 92.5};
 
 std::cout << "Name: " << s1.name << std::endl; // Alice
 std::cout << "Age: " << s1.age << std::endl; // 20
 std::cout << "Score: " << s1.score << std::endl; // 92.5
 
 return 0;
}

(2) 4.2 Modifying Members

TEXT 📖 Display only

Student s1 = {"Alice", 20, 92.5};
s1.score = 95.0; // Modify the score
std::cout << "New score: " << s1.score << std::endl; // 95.0

5. Passing Structs as Function Parameters

(1) 5.1 Pass by Value (Not Recommended)

CPP

void printStudent(Student s) { // ❌ Pass by value: copies the entire struct, expensive
 std::cout << "Name: " << s.name << std::endl;
}

(2) 5.2 Pass by Reference (Recommended)

TEXT 📖 Display only

void printStudent(const Student& s) { // ✅ Pass by reference: no copy, and cannot modify
 std::cout << "Name: " << s.name << std::endl;
 std::cout << "Age: " << s.age << std::endl;
 std::cout << "Score: " << s.score << std::endl;
}

💡 Golden Rule: When passing a struct as a parameter, prefer const reference — it avoids copy overhead and prevents accidental modification.

6. Arrays of Structs

Structs can also be organized into arrays!

Example: Student Array (Difficulty ⭐⭐)

CPP

#include <iostream>
#include <string>

struct Student {
 std::string name;
 int age;
 double score;
};

int main() {
 Student students[3] = {
 {"Alice", 20, 92.5},
 {"Bob", 21, 88.0},
 {"Charlie", 19, 95.0}
 };
 
 // Iterate over the struct array
 for (int i = 0; i < 3; i++) {
 std::cout << "========== Student " << i + 1 << " ==========" << std::endl;
 std::cout << "Name: " << students[i].name << std::endl;
 std::cout << "Age: " << students[i].age << std::endl;
 std::cout << "Score: " << students[i].score << std::endl;
 std::cout << std::endl;
 }
 
 return 0;
}

7. Practice: Student Grade Management (Struct Version)

▶ Example 1: Complete Student Grade Management (Difficulty ⭐⭐⭐)

TEXT 📖 Display only

#include <iostream>
#include <string>
#include <vector> // will learn vector later, using array for now

struct Student {
 std::string name;
 int age;
 double score;
};

// Function declaration
void addStudent(Student students, int& count);
void printStudents(const Student students, int count);
double calculateAverage(const Student students, int count);

int main() {
 const int MAX_STUDENTS = 100;
 Student students[MAX_STUDENTS];
 int count = 0;
 
 int choice;
 do {
 std::cout << "========== Student Score Management ==========" << std::endl;
 std::cout << "1. Add student" << std::endl;
 std::cout << "2. Display all students" << std::endl;
 std::cout << "3. CalculateAverage" << std::endl;
 std::cout << "4. Exit" << std::endl;
 std::cout << "Please select (1-4): ";
 std::cin >> choice;
 
 if (choice == 1) {
 addStudent(students, count);
 } else if (choice == 2) {
 printStudents(students, count);
 } else if (choice == 3) {
 if (count == 0) {
 std::cout << "No student data!" << std::endl;
 } else {
 std::cout << "Average: " << calculateAverage(students, count) << std::endl;
 }
 } else if (choice == 4) {
 std::cout << "Goodbye!" << std::endl;
 } else {
 std::cout << "Error: Please enter 1-4 a number between 1-4!" << std::endl;
 }
 
 std::cout << std::endl;
 
 } while (choice != 4);
 
 return 0;
}

// Function definition
void addStudent(Student students, int& count) {
 if (count >= 100) {
 std::cout << "Maximum number of students reached!" << std::endl;
 return;
 }
 
 std::cout << "Please enter your name: ";
 std::cin.ignore();
 std::getline(std::cin, students[count].name);
 
 std::cout << "Please enter your age: ";
 std::cin >> students[count].age;
 
 std::cout << "Please enter score: ";
 std::cin >> students[count].score;
 
 count++;
 std::cout << "Added successfully!" << std::endl;
}

void printStudents(const Student students, int count) {
 if (count == 0) {
 std::cout << "No student data!" << std::endl;
 return;
 }
 
 std::cout << "\n========== Student List ==========" << std::endl;
 for (int i = 0; i < count; i++) {
 std::cout << i + 1 << ". Name: " << students[i].name 
 << "，Age: " << students[i].age 
 << "，Score: " << students[i].score << std::endl;
 }
 std::cout << "================================\n\n";
}

double calculateAverage(const Student students, int count) {
 if (count == 0) {
 return 0.0;
 }
 
 double sum = 0.0;
 for (int i = 0; i < count; i++) {
 sum += students[i].score;
 }
 
 return sum / count;
}

Output:

TEXT 📖 Display only

========== Student Score Management ==========
1. Add student
2. Display all students
3. CalculateAverage
4. Exit
Please select (1-4): 
No student data!
Average: 
Goodbye!
Error: Please enter 1-4 a number between 1-4!
Maximum number of students reached!
Please enter your name: 
Please enter your age: 
Please enter score: 
Added successfully!
No student data!

========== Student List ==========
. Name: 
===============================

▶ Example 3: Struct as a Function Return Value (Difficulty ⭐)

CPP

#include <iostream>
#include <string>

struct Student {
    std::string name;
    int age;
    double score;
};

// Function that returns a struct
Student createStudent(std::string n, int a, double s) {
    Student stu;
    stu.name = n;
    stu.age = a;
    stu.score = s;
    return stu;
}

int main() {
    Student s1 = createStudent("Zhang San", 20, 92.5);
    
    std::cout << "Name: " << s1.name << std::endl;
    std::cout << "Age: " << s1.age << std::endl;
    std::cout << "Score: " << s1.score << std::endl;
    
    return 0;
}

▶ Try it Yourself

Output:

TEXT 📖 Display only

Name: 
Age: 
Score:

💡 Tip: Structs can be used as function return values for creating and initializing struct objects.

8. Common Mistakes

(1) 8.1 Forgetting the Semicolon

Error Example:

TEXT 📖 Display only

struct Student { // ❌ Forgot the semicolon
 std::string name;
 int age;
 } // ❌ There should be a semicolon here

int main() {
 // ...
}

Compiler Error Message:

TEXT 📖 Display only

error: expected ';' after struct definition

(2) 8.2 Accessing a Non-Existent Member

Error Example:

CPP

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

int main() {
 Student s1;
 s1.score = 92.5; // ❌ Error: Student has no score member
 return 0;
}

❓ FAQ

Q What's the difference between a struct and a class?

A We'll cover classes in detail later, but briefly: > - struct has default access of public > - class has default access of private

Q: What's the most important thing about struct basics? A: Understand the core concepts first, then reinforce them through practice examples.

📖 Summary

Structs combine multiple variables of different types into a single unit
Declaring a struct: struct StructName { member list }; (note the semicolon!)
Initialization: StructName variableName = {value1, value2, ...};
Accessing members: variableName.memberName
When passing as a parameter, prefer const reference
Structs can also be organized into arrays

📝 Exercises

Basic (Difficulty ⭐): Define a Book struct with three members: title, author, and price. Create two Book variables and output them.
Intermediate (Difficulty ⭐⭐): Define a Rectangle struct with two members: width and height.
Write a function double calculateArea(const Rectangle& r) to calculate the area
Write a function double calculatePerimeter(const Rectangle& r) to calculate the perimeter
Test in main
Challenge (Difficulty ⭐⭐⭐): Define a Date struct (year, month, day), and write a function to check whether a date is valid (e.g., 2024-02-29 is valid, 2023-02-29 is invalid).

Struct: packages different types of data into a single unit
Member access uses the . operator; pointers use ->
Initialization: uniform initialization {} or member-by-member assignment
Structs can be used as function parameters and return values
Struct arrays manage multiple records

9. 🚀 Next Steps

Now that you've learned structs, let's move on to Phase 4 (Pointers & References) — the most core and challenging part of C++, but mastering it will let you write more efficient code!

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C++: Struct Basics

1. What Is a Struct?

(1) 1.1 Structs in Everyday Life

(2) 1.2 Why Do We Need Structs?

▶ Example 2: Code Example (Difficulty ⭐)

2. Declaring and Defining Structs

(1) 2.1 Declaring a Struct

3. Creating and Initializing Struct Variables

(1) 3.1 Creating a Struct Variable

(2) 3.2 Initializing a Struct Variable

4. Accessing Struct Members

(1) 4.1 Reading Members

(2) 4.2 Modifying Members

5. Passing Structs as Function Parameters

(1) 5.1 Pass by Value (Not Recommended)

(2) 5.2 Pass by Reference (Recommended)

6. Arrays of Structs

7. Practice: Student Grade Management (Struct Version)

▶ Example 1: Complete Student Grade Management (Difficulty ⭐⭐⭐)

▶ Example 3: Struct as a Function Return Value (Difficulty ⭐)

8. Common Mistakes

(1) 8.1 Forgetting the Semicolon

(2) 8.2 Accessing a Non-Existent Member

❓ FAQ

📖 Summary

📝 Exercises

9. 🚀 Next Steps

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