Introduction to programming in C++
Posted by Samath
Last Updated: March 08, 2012
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As the worlds increasing use of computer technology in the digital era continues apace, it becomes ever more vital for engineers and developers to have a better understanding of the technical processes at work in this ubiquitous and dynamic state of affairs.

This is especially true for programmers who’ll be building the future software we’ll be using in our devices and machines in years to come which we’ve already taken advantage of so much and come to rely on in recent years. 

Though C++ has only been around for about half the time that computer programming itself has been in existence (25 years compared to 50), in this time, it’s arguably become the most important programming language for half a century. 

Its complexity is both to its advantage and disadvantage. On the one hand, virtually no other language is better placed to deal with the challenges and demands created by the need for ever more sophisticated software. On the other, it has an extremely rich feature set that can seem intimidating to some at first glance. 

In this series of tutorials, we’ll be looking at the language from the ground up and forming a better understanding of programming along the way. 

For readers who’ve never written a program before, I’ll state here and now that there’s nothing to fear. The tiger you’ve been afraid of all this time is nothing more than a pussy cat. 

Although C++ is an extremely powerful language (it’s capable of building just about any type of computer program) it’s also intuitive to use and once insight into it is gained will become a great ally in projects and challenges that come your way.

Gaining such understanding isn’t difficult and I’ll guide you every step of the way to the conclusion where you’ll be building complex programs to be proud of. So let’s begin.

What is a computer program anyway? Nothing more than a series of instructions supplied to a computer to perform a given task – that’s what.

When examined under the surface in greater detail, this statement encompasses a whole number of things.

The first thing is the concept of an algorithm. What is an algorithm? More or less the same thing (a series of instructions etc) described in actual programming terms.

To be absolutely accurate, an algorithm is a series of steps followed by a computer program – and each step is an instruction – which the program gives to the hardware (the machinery) that comprises the computer.

Here’s an example of an algorithm. It works out how old someone is.

1.Get the current year

2.Get the person’s birth year

3.Subtract the number of years in the birth year from the current year

4.Output the result (the persons age)

A very simple example, I think you’ll agree. But in this simple document lies in essence what an algorithm –and a computer program are all about – clear, detailed steps (sometimes dizzying in their complexity for large programs) providing instructions to a computer via a piece of software.

Basically, a computer program is the expression of an algorithm. The algorithm is manifested in the program.

Another useful point to bear in mind is that virtually any algorithm (especially if it’s a complicated one) can be written in almost any number of ways. But I digress, so let’s move on.

As ever in life, things are simple – but not that simple. If a programmer literally fed those instructions into her PC, at worst she’d get a rude message (something and something or other is undefined – in other words I don’t know what you’re talking about) or at best (more likely) nothing would happen at all.

You see, computers don’t (yet) understand human languages. In fact, they don’t understand very much at all (except one thing – more about it later).

Computer programming languages come in two varieties – high level languages and low level languages. Most modern languages (like C++) are high level.

High level languages are alpha numeric – that is, they are made up of alphabetical and numerical characters (or letters and numbers to you non-geeks) in their syntax (or language structure) which makes them easier to read and understand.

As mentioned earlier however, computers find what we intuitively understand completely perplexing. So we have to translate – or rather a particular type of software does this for us. This software is called a compiler.

When a computer program is written in a high level language like C++ before the computer can understand the programmer’s instructions, the instructions (or code) need to be compiled.

The compilation of a program is a process which occurs in between the writing of it and its execution (when it runs as software in front of you on the screen).

Compilers are computer programs, sometimes used separately but often built within the programmer’s IDE (Integrated Development Environment – a computer program for writing computer programs) that perform this task.

When a program is compiled it turns into something called machine code. The content of this code is simply a series of ones and zeroes and if it sounds familiar, you’re absolutely right because another name for machine code is binary code.

Since the dawn of the age of modern computing, computers have understood instructions in this form that we all learned at school where a sequence of ones and zeroes indicates a value built from multiples of two increasing by the power of two with each digit to the left.

The reason computers use this system is simplicity (computers are pretty simple at heart, bless) where each zero symbolises an ‘off’ and each 1 symbolises an ‘on’. Taken as a whole, a complete sequence in binary code made from a succession of on-off switches form a set of instructions that equate to ‘yes’ or ‘no’ or ‘do’ or ‘don’t’. Should I make the tea? Yes. Shall I jump off this cliff? No. Can I give you a massage? Do. Do I crash the car? Don’t! And so on…

So basically that’s the language of computers (plus all the electronic machines and devices you use every day) and it’s pretty dull (see how long you can stare at a long stream of binary code before falling asleep – or getting dizzy). But the binary system has informed everything in computing from circuit design to the construction of the multi-core processor to the distribution of global networks – so it’s pretty important.

As mentioned, there are high level languages and low level languages. Use of low level languages isn’t as common any more as the use of high level ones.

One famous low level language is Assembly. It and other development systems like it are called low level languages because they communicate more directly with hardware.

Assembly resembles machine code in its structure and because it’s understandable and more native to the machinery of a PC it works faster. This is useful for operations where speed is critical – such as the execution of instructions by a Graphical Processing Unit (GPU) or code in a game that computes a lot of information very fast.

Going into further detail on the alpha numeric nature of high level languages – the content of C++ is actually made up of familiar key words in English – which translate to instructions that will become recognisable to the machine when the code is compiled.

These key words define entities with generic names like function, variable and expression. In many languages (C++ included) for clarity, the unique names of examples of these entities are preceded by their generic names – e.g. function: Get Coffee.

Such key words are known as reserved words, meaning they can’t be used in user defined examples because they’re already built into the language itself. User defined basically means an example of an entity or object created by the programmer.

So for example, a programmer couldn’t create a function called Function. They would receive an error message telling them that the word ‘function’ is a reserved word.

Let’s examine what these objects actually are, starting with variables.

A variable is essentially a container for information that changes – hence the name, variable – derived from variation – a change.

Variables are categorized into different types called data types. Data type is simply a programming term for ‘different type of information’. There are a considerable number of data types in C++ (which we’ll encounter in future tutorials) but the ones most commonly used are integer (for numeric information) and string (for text based information).

As it happens, C++ is particularly good with numbers and as one might expect, there are many variations for integer variables so to speak.

Here are some examples.

This is a C++ string variable:

char Name = Theodore;

The ‘char’ word is a keyword in C++ for the ‘Character’ data type. ‘Character’ is used for strings or pieces of text data. In C++ every variable must be defined first with a data type.

The word ‘Name’ is simply a string variable I’ve created and its value is my name.

The semi-colon on the end of the line is a character you need to include at the end of each line of code –or statement - in C++ (and other languages).

It indicates that the particular instruction is complete and the computer can move to the next line.

This is an integer variable:

int currentage = 44;

The ‘int’ keyword is short for ‘integer’. Integers are used for numeric data. I’ve named this example of an integer ‘currentage’ and it’s value is my age which is 44.

We’ll be looking at variables in greater detail in tutorial 3 in this series.

Next up are expressions. Expressions are statements which return a value. Here’s an example of an expression.

currentyear – birthyear = currentage;

currentyear and birthyear are both integers containing number values providing information on the number of years in the current year and the number of years in someone’s birth year.

When birthyear uses the mathematical operator (the minus) between it and currentyear to subtract from currentyear, the result is placed in another integer, the currentage integer.

All expressions behave in the same way. An expression is basically a calculation and once performed generates a result or in programmer speak, ‘returns a value’.

The next step from writing statements is to write a function. A function is simply a collection of related statements that focus on a particular task. Here’s an example:

#include "stdafx.h"

#include

using namespace std;

int FindTime (int distance, int speed)

{

int time;

time = distance/speed;

return (time);

}

int main () {

int distance = 0;

int speed = 0;

int time = 0;

cout > distance;

cout > speed;

using namespace std;

int main(void)

{

int birthyear = 0;

int currentyear = 0;

int currentage = 0;

//Get the person’s birth year

cout > birthyear;

//Get the current year

cout > currentyear;

//Subtract the number of years in the person’s birth year from the number of

//years in the current year

currentage = currentyear - birthyear;

cout << "you are currently:

" << currentage << "years old";

return 0;

}

And there we are. As you’ve seen from the code above, programming isn’t rocket science (though it’s a very useful tool for the maths and physics involved in rocket science).

   
  
 
 
   

 
 
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