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.

Exercise 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.

Show example solution

#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;
}

Test yourself

Fill in the blank: vector declaration

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

Show answer

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

Which header is required for vector<Point>?
- <string>
- <vector>
- <array>
- <list>
Show answer

<vector> — The <vector> header is required for vector.
Match each method with its job

push_back

adds to the end
size

returns the length
[i]

gives the i-th element

Next lesson: Nested structs

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