C-and-C++/C2/First-C++-Program/English

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Title of script: First C++ program

Author: Ashwini

Keywords: int main(),


Visual Cue
Narration
Slide 1 Welcome to the spoken tutorial on First C++ program.
Slide 2

Learning Objectives

In this tutorial I am going to explain,

How to write a C++ program.

How to compile it.

How to execute it.

We will also explain some common errors and their solutions.

Slide 3

System Requirements


To record this tutorial, I am using

Ubuntu operating system version 11.10

and G++ Compiler version 4.5.2 on Ubuntu.

Slide 4

Prerequisites


To practice this tutorial,

You should be familiar with Ubuntu Operating System

and an Editor

Some editors are vim, gedit.

I am using gedit in this tutorial.

For relevant tutorial Please visit our website:

http://spoken-tutorial.org

Open the Terminal


Open the terminal using Ctrl + Alt + T

Let me tell you how to write a C++ program through an example

Open terminal Window using Ctrl, Alt and T keys simultaneously on your keyboard.

gedit talk.cpp & To open the text editor, type

“gedit” space “talk” dot “.cpp” space ampersand “&”.

Highlight & We use the “&” to free up the prompt.
Highlight .cpp Please note that all the C++ files will have the extension “.cpp”
Now Press Enter

The text editor has opened.

Let us start to write a program.
//My first C++ program Type double slash “//” space

“My first C++ program”.

Highlight // Here, double slash is used to comment the line

Comments are used to understand the flow of program

It is useful for documentation

It gives us information about the program

The double slash is called as single line comment.

Type #include <> Now press Enter

Type hash “#include” space opening angle bracket “<” closing angle bracket “>”.

It is a good practice to complete the brackets first, and then start writing inside it

Type #include <iostream> Now, inside the bracket, type

“iostream”.

Here iostream is a header file

This file includes the declaration of basic standard input output library in C++.

Type using namespace std; Now press Enter

Type “using” space “namespace” space “std” and a semicolon “;”

Highlight using


Highlight namespace


Highlight std

The using statement informs the compiler that you want to use the std namespace

The purpose of namespace is to avoid name collisionsis

It is done by localizing the names of identifiers

It creates a declarative region and defines a scope

Anything defined within a namespace is in the SCOPE of that namespace

Here, std is the namespace in which entire standard C++ library is declared.

Type int main() Now Press Enter.

Type “int” space “main” opening bracket “(” closing bracket “)” .

Highlight main() Main is a special function

It denotes that the execution of the program begins from this line.

The opening and the closing bracket is called as parenthesis.

Highlight () Parenthesis followed by main is to tell the user that main is a function.
Highlight int main() Here the int main function takes no arguments and returns a value of type integer.
We will learn about data types in another tutorial.
Now let us switch to the slides to know more about the main function.
Every program will have only one main function

There should NOT be more than one “main” function

Otherwise the compiler cannot locate the beginning of the program

The empty pair of parentheses indicates that main has no arguments

The concept of arguments will be discussed in detail in the upcoming tutorials.

Now come back to our program.

Type { press Enter.

Type opening curly bracket “{”

The opening curly bracket marks the beginning of the function main.

Type } Type closing curly bracket “}”

The closing curly bracket indicates the end of the function main.

Inside the bracket press enter twice

Move the cursor one line up.

Indentation makes the code easier to read

It also helps to locate errors faster.

So let us give a space here.

Type cout << And type “cout” space two opening angle bracket “<<” space .
Highlight cout<< Here cout is a standard C++ function to print the output

And << is an output operator.

Type

cout << “Talk to a teacher\n”

Now after the brackets, type

within the double quotes “Talk to a teacher backslash \n”.

Highlight “” Anything within the double quotes in the cout << statement will be printed.
Highlight \n \n signifies newline

As a result, after execution of the cout function, the cursor moves to the new line.

Type

“;”

Every C++ statement must end with a semicolon

Hence type it at the end of this line.

Highlight ; Semicolon acts as a statement terminator.
Type

return 0;

Now press Enter

Type “return” space “0” and a semicolon “;”.

Highlight return 0;


Highlight int

This statement returns the integer zero.

An integer has to be returned for this function.

Because the function type is int.

The return statement marks the end of executable statements.

We will learn more about the returned values in another tutorial.

Save Now click on the “Save” button to save the file.

It is a good habit to save files frequently.

This will protect you from sudden power failures.

It will also be useful in case the applications were to crash.

Compile Let us now compile the program.
Type

g++ talk.cpp -o output

Please open the terminal

Type “g++” space “talk.cpp” space hyphen “-o” space “output”.

Highlight g++

Highlight talk.cpp

Highlight -o output

g++ is the compiler used to compile C++ programs

talk.cpp is the filename

on compilation g++ creates an executable

-o output says that the executable should go to the file output.

We see that the program is compiled.
Type

ls -lrt

By typing ls -lrt, we can see that output is the last file to be created.
Type

./output

To execute the program,

type dot slash “./output”

Press Enter.

Highlight Talk to a teacher Here the output is displayed as “Talk to a teacher”.
Errors


Now let us see the common errors which we can come across

Please switch to the editor.

{ Suppose we miss the {

I will retain rest of the code as it is.

save the program.
Let us execute it again

Let us go to the terminal

Now compile and run the program using the command we used before.
Highlight error

Highlight Line no.7

Highlight talk.cpp

Highlight {

we see that there is an error at line no.7 in our talk.cpp file

Expected curly bracket at the end of input.

Come back to out program.
As i said before the closing curly bracket marks the end of the function main

Hence reinsert the bracket .

Save it.
Let us execute it

You can recall the previously entered commands by using up arrow

That is what I did now

Yes it is working.

Error 2 I will show you another common error

Let us switch back to the editor.

Now, suppose here we missed std.
Save it.
Highlight error

Highlight Line no.3 and 6

Highlight talk.cpp

Highlight ;

Highlight cout

Compile and run it as before

We see that there are errors at line no 3 and 6 in our talk.cpp file

expected identifier before semicolon

and cout was not declared in this scope.

As cout is the standard C++ library function

and the entire C++ library function is defined under std namespace

Hence it is giving an error.

Let us fix the error

Come back to our program

type std.

Save it.
Let us execute it

Yes it is working.

As an assignment,

Write a program to print your name and city

We used single line comment in this tutorial

Now just try to give multiline comment

Hint:

/*..................

.....................*/

Slide 8

About the Spoken Tutorial Project


Watch the video available at the link shown

http://spoken-tutorial.org /What\_is\_a\_Spoken\_Tutorial

It summarises the Spoken Tutorial project

If you do not have good bandwidth, you can download and watch it.

Slide Number 9

Spoken Tutorial Workshops


The Spoken Tutorial Project Team

Conducts workshops using spoken tutorials

Gives certificates to those who pass an online test

For more details, contact spoken-tutorial.org

Slide Number 10


Acknowledgement

Spoken Tutorial Project is a part of the Talk to a Teacher project

It is supported by the National Mission on Education through ICT, MHRD, Government of India

More information on this Mission is available at: http://spoken-tutorial.org\NMEICT-Intro

This is Ashwini Patil from IIT Bombay signing off

Thank you for joining

Contributors and Content Editors

Ashwini, PoojaMoolya