Object oriented programming is one of the perks to C++ (and Java). This tutorial is about data structures. Data structures are a great introduction to object oriented programming. I will go more in depth into OOP in later tutorials. This is part 19 of my C++ tutorials. If you want to check out my other tutorials in this series, here they are:

Part 1: Hello World!

Part 2: Variables

Part 3: Functions

Part 4: if(), else, else if()

Part 5: Loops

Part 6: Arrays

Part 7: Basic Input/Output

Part 9: Sorting Arrays

Part 10: Random Numbers

Part 11: Colored Text in your Terminal

Part 12: Recursion

Part 13: Binary Search

Part 14: 2D Arrays

Part 15: String Processing

Part 16: Binary, Bitwise Operators, and 2^n

Part 17: Pointers

Part 18: Pointer Arithmetic

Declaring Data Structures

A data structure is basically just what it sounds like. It is a clump of code designed to be a structure for something else. Here is how to declare a structure:

struct name
{
    //members go here
} /* object names go here*/ ;

name is the name of the structure
members are just variables that make up, or describe, the structure
object names are where you declare specific objects

Here is a more specific example:

struct employee
{
    string name;
    int id;
    float pay_rate;
} fred, bob, susanne;

employee is a data structure that will describe different employees
the variable name will hold the name of each employee
the variable id will hold the ID number of each employee
the variable pay_rate will hold the pay rate of each employee
fred, bob, and susanne are names of different employee objects
Note: do not initialize any variables in the struct; they will be initialized later, for each employee

Using the Objects

First, you can also declare objects later in main() like this:

employee  fred, bob, susanne;

To initialize the members of the structure, type in the object name, a period, then the member name. Here is an example with fred:

fred.name = "Fred";
fred.id = 12345;
fred.pay_rate = 7.25;

This can be done with all of the objects that were initialized. Each object has its own members (fred.name is different than bob.name).

You can also pass objects to a function. Here is a program I wrote that does that:

#include
#include
using namespace std;

struct animal
{
    string name;
    string color;
    int num_legs;
};

void printA(animal a)
{
    cout << a.name
    << "s are "
    << a.color
    << ", and have "
    << a.num_legs
    << " legs.\n";
}

int main()
{
    animal dog, bird, spider;
    
    dog.name = "Dog";
    dog.color = "brown";
    dog.num_legs = 4;

    bird.name = "Bird";
    bird.color = "green";
    bird.num_legs = 2;

    spider.name = "Spider";
    spider.color = "black";
    spider.num_legs = 8;

    printA(dog);
    printA(bird);
    printA(spider);

    return 0;
}

struct animal --> a structure to describe different animal objects
- name --> a string to hold the name of the animal
- color --> a string to hold the color of the animal
- num_legs --> an integer that holds how many legs the animal has
printA() --> prints a description of an animal
- a --> an animal object (notice its type is animal)
- print the description (name, color, and number of legs)
main()
- create 3 animal objects: dog, bird, and spider
- initialize all of the attributes of each animal
- call printA() for every animal object

Here is the output:

[cmw4026@omega test]$ g++ animal.cpp
[cmw4026@omega test]$ ./a.out
Dogs are brown, and have 4 legs.
Birds are green, and have 2 legs.
Spiders are black, and have 8 legs.
[cmw4026@omega test]$