Member Variables and Member Selection

Member Variables and Member Selection

The key to reading or changing a struct is the member selection operator - the dot .. It connects an object with one of its members.

A struct full of members

#include <iostream>
using namespace std;

struct Person {
  string name;
  int age;
};

int main() {
  Person bob;
  bob.name = "Bob";
  bob.age = 80;

  cout << bob.name << endl;   // Bob
  return 0;
}

The members name and age are member variables: ordinary variables that live inside each Person object.

Reading a member

string whom = bob.name;    // copy the member out
cout << bob.age;           // use it directly

Writing a member

The dot also works for assignment:

bob.age = 80;      // store the value on the right
bob.name = "Bob";  // replace the old name

Members behave like normal variables

A member supports everything its type supports - assign, print, compare, do math. It just belongs to the object instead of living alone.

Arrays of structs

A struct is a type, so it can be the element type of an array:

int main() {
  Person team[3];

  team[0].name = "Alice";
  team[0].age = 25;

  team[1].name = "Bob";
  team[1].age = 80;

  cout << team[0].name << endl;   // Alice
  return 0;
}

• team[0] selects the first object.
• .name then selects its member.
• Combined: team[0].name.

TL;DR

• Members are the variables that live inside an object.
• The dot erases a member: cout << bob.name;.
• The dot writes a member: bob.age = 80;.
• team[0].name = pick the element first, then the member.
• Member variables act like ordinary variables of their type.