Written by John Pham

Modified by Josh Beto

Lesson Plan

This week we’ll be covering creating our own custom classes with structs and classes.

Structs

Structs allow us to create a new data type that groups together relevant data. If we wanted to keep track of a student say their name, age, and gender, normally we would have to create 3 separate variables to store that information.

string name = "";
int age = 0;
string gender = "";

If we had tons of students we would have to rename the variables for each students.

string name1 = "";
int age1 = 0;
string gender1 = "";

string name2 = "";
int age2 = 0;
string gender2 = "";

As you can see, this could get quite messy if we have to track a class worth of students. Structs allow us to group all 3 variables into a new data type.

struct Student {
  string name;
  int age;
  string gender;
}

Student student1 = {"Bobo", 19, "Male"};
Student student2 = {"Lula", 19, "Female"};

Each variable inside a struct is referred to as a data member of the struct. If we wanted to access an individual data member, we would use the dot operator.

struct Student {
  string name;
  int age;
  string gender;
}

Student student1 = {"Bobo", 19, "Male"};

// this will output: "Bobo19Male"
cout << student1.name << student1.age << student1.gender << endl;

We can also reassign the values after the data members were initialized, again using the dot operator.

struct Student {
  string name;
  int age;
  string gender;
}

Student student1 = {"Bobo", 19, "Male"};

// this will output: "Bobo19Male"
cout << student1.name << student1.age << student1.gender << endl;

student1.age = 20;
// this will output: "Bobo20Male"
cout << student1.name << student1.age << student1.gender << endl;

Since structs are just new data types, we can use them in any situation that we use other types such as a return type for a function and the data type of a vector.

Classes

Moving forward, we’ll starting learning about Object Oriented Programming. This type of programming sets you to model your code’s data as real life objects. Transactions, people, cars, basically anything can be modeled as an object in a program. You saw earlier that we were able to model a student in a struct. Structs however are quite limited on what they can do. Let’s take a look at classes.

class Student {
  public:
    void setName(string name);
    string getName();

    void setAge(int age);
    int getAge();

    void setGender(string gender);
    string getGender();
  private:
    string name;
    int age;
    string gender;
}

The above code shows our student struct rewritten as a class. This looks like a lot more work to accomplish the same thing but it allows us to define exactly what a Student can do.

Items under the public: keyword can be accessed outside of the class while items under private: can only be accessed within the class. This allows us to do error checking inside our public methods before reassigning the values of the private data members.

Key Concepts

• Accessors (Getters)
• Mutators (Setters)
• Constructors
  • Default
  • Explicit
• The implicit parameter
  • this->

Exercises

• Write a program that implements the following:
  • Define a custom struct Animal with the following parameters:
    • name - the name of the animal
    • species - what kind of animal it is i.e. pig horse dog
    • age - how old the animal is
  • Write a function that takes in a vector<Animal> and prints that vector. The function should output the content of each animal as follows:
    • Name: actual_name
    • Species: actual_species

    • Age: actual_age

    • (Next Entry)
  • Write a main that fills avector<Animal> with the following information:

     Name: Jessie
     Species: Dog
     Age: 3
    
     Name: Colbert
     Species: Pig
     Age: 5
    
     Name Violet
     Species: Horse
     Age: 7
    

    • Print out the vector<Animal> according to the function specified above.