Difference between revisions of "C-and-C++/C2/First-C++-Program/English"

Learning Objectives

How to write a C++ program.

How to compile it.

How to execute it.

We will also explain some common errors and their solutions.

System Requirements

Ubuntu operating system version 11.10

and G++ Compiler version 4.5.2 on Ubuntu.

Prerequisites

You should be familiar with Ubuntu Operating System

and an Editor

Some editors are vim, gedit.

I am using gedit in this tutorial.

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Open the terminal using Ctrl + Alt + T

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

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

The text editor has opened.

“My first C++ program”.

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 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

“iostream”.

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

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

Highlight namespace

Highlight std

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

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

The opening and the closing bracket is called as parenthesis.

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 the upcoming tutorials.

Now come back to our program.

Type opening curly bracket “{”

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

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

Inside the bracket press enter twice

Move the cursor one line up.

It also helps to locate errors faster.

So let us give a space here.

cout << “Talk to a teacher\n”

within the double quotes

Now inside the quotes type “Talk to a teacher backslash \n”.

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

“;”

Hence type it at the end of this line.

return 0;

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

Highlight int

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.

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.

g++ talk.cpp -o output

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

Highlight talk.cpp

Highlight -o output

talk.cpp is the filename

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

ls -lrt

./output

type dot slash “./output”

Press Enter.

Please switch to the editor.

I will retain rest of the code as it is.

Let us go to the terminal

Highlight Line no.7

Highlight talk.cpp

Highlight {

Expected curly bracket at the end of input.

Hence reinsert the bracket .

You can recall the previously entered commands by using up arrow key

That is what I did now

Yes it is working.

Let us switch back to text editor.

Highlight Line no.3 and 6

Highlight talk.cpp

Highlight ;

Highlight cout

We see that there is an error at line no 3 and 6 in our talk.cpp file that

expected identifier before semicolon

and cout was not declared in this scope.

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

Hence it is giving an error.

Come back to our text editor.

type std. here

Yes it is working.

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:

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

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

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