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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<iostream>
#include<string>
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]$

I hope this was simple enough! Leave suggestions in the comments.