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Array of structs

Learn to create a vector of structs and iterate it.

Creating a vector of structs

To manage many instances of the same struct, you use a vector. The declaration vector<Point> creates a dynamic array whose elements are Point values.

vector<Point> points;
Point p;
p.x = 1;
p.y = 2;
points.push_back(p);

Here points is a vector of Point; push_back adds a new element. Elements are accessed like points[0].x. The #include <vector> header is required.

Iterating with a loop

To walk through all elements of a struct vector, you use a loop. The easiest way is the range-based for loop.

for (Point p : points) {
    cout << p.x << ", " << p.y << endl;
}

Here the loop copies each element into p in turn. To iterate without copying, use for (const Point& p : points). The range-based loop is a short way to walk through all elements without knowing the vector's length.

Practice Add two Points and iterate

Add the #include <vector> header. Declare vector<Point> points;. Create two Points and add them with points.push_back(...); the first has x=1, y=2, the second x=3, y=4. Use a range-based for to print each element's x and y.

Starter code

main.cpp
#include <iostream>
#include <vector>
using namespace std;

struct Point {
    int x;
    int y;
};

int main() {
    // declare a Point vector, add two Points, print with for
    return 0;
}

Sample solution

main.cpp
#include <iostream>
#include <vector>
using namespace std;

struct Point {
    int x;
    int y;
};

int main() {
    vector<Point> points;
    Point a; a.x = 1; a.y = 2;
    Point b; b.x = 3; b.y = 4;
    points.push_back(a);
    points.push_back(b);
    for (Point p : points) {
        cout << p.x << ", " << p.y << endl;
    }
    return 0;
}

Expected output

1, 2
3, 4

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Fill in the blank: vector declaration

Question 
#include <vector>
using namespace std;
vector<Point> ____;
points.push_back(p);
Answer 
#include <vector>
using namespace std;
vector<Point> points;
points.push_back(p);

Explanation: A vector<Point> named points was created.

2 Which header is required for vector<Point>?

  • <string>
  • <vector> Correct answer
  • <array>
  • <list>

Explanation: The <vector> header is required for vector.

3 Match each method with its job

Term Meaning
push_back adds to the end
size returns the length
[i] gives the i-th element

All lessons in Beginner

1 C++ basics

  1. What is C++?
  2. Your first program
  3. std::cout
  4. std::cin
  5. Comments
  6. Summary - C++ basics

2 Variables

  1. Declaring variables
  2. auto
  3. const
  4. constexpr
  5. Type conversion
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. bool and char
  4. std::string
  5. sizeof
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Bitwise operators
  6. Summary - Operators

6 Strings

  1. std::string basics
  2. String concatenation
  3. String length
  4. Substring
  5. String search
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. The switch statement
  4. The ternary operator
  5. Nested conditionals
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. Range-based for
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding products
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. C-style arrays
  2. Array access
  3. std::array
  4. Multidimensional arrays
  5. Arrays and loops
  6. Summary - Arrays

11 std::vector

  1. Declaring vectors
  2. push_back
  3. size and at
  4. Vector access
  5. Vector loop
  6. Summary - std::vector

12 Functions

  1. Defining functions
  2. Return values
  3. Parameters
  4. Function overloading
  5. Default parameters
  6. Summary - Functions

13 References

  1. What is a reference?
  2. Declaring references
  3. Reference parameters
  4. const references
  5. Dangling references
  6. Summary - References

14 Pointer basics

  1. What is a pointer?
  2. The & address operator
  3. Pointer dereference
  4. nullptr
  5. Pointer arithmetic
  6. Summary - Pointer basics

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. String streams
  2. stoi and stod
  3. to_string
  4. String comparison
  5. String modification
  6. Summary - Advanced strings

17 Structs

  1. Defining structs
  2. Using structs
  3. Struct and function
  4. Array of structs
  5. Nested structs
  6. Summary - Structs

18 Exception basics

  1. try/catch
  2. throw
  3. std::exception
  4. Custom exceptions
  5. catch all
  6. Summary - Exceptions

19 Namespaces

  1. Defining namespaces
  2. using
  3. std namespace
  4. Nested namespaces
  5. Namespace alias
  6. Summary - Namespaces

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together