Commit c296bdad authored by GILLES Sebastien's avatar GILLES Sebastien
Browse files

Add paragraph about comments.

parent 1d1ef6c6
......@@ -14,7 +14,7 @@
},
"source": [
"<h1>Table of contents<span class=\"tocSkip\"></span></h1>\n",
"<div class=\"toc\"><ul class=\"toc-item\"><li><span><a href=\"#About-the-choice-of-a-Jupyter-notebook\" data-toc-modified-id=\"About-the-choice-of-a-Jupyter-notebook-1\">About the choice of a Jupyter notebook</a></span></li><li><span><a href=\"#When-the-notebook-is-not-enough...\" data-toc-modified-id=\"When-the-notebook-is-not-enough...-2\">When the notebook is not enough...</a></span></li><li><span><a href=\"#Few-guidelines-about-Jupyter\" data-toc-modified-id=\"Few-guidelines-about-Jupyter-3\">Few guidelines about Jupyter</a></span><ul class=\"toc-item\"><li><span><a href=\"#Restarting-the-kernel\" data-toc-modified-id=\"Restarting-the-kernel-3.1\">Restarting the kernel</a></span></li></ul></li><li><span><a href=\"#Very-basic-C++-syntax-(in-notebook-and-in-general)\" data-toc-modified-id=\"Very-basic-C++-syntax-(in-notebook-and-in-general)-4\">Very basic C++ syntax (in notebook and in general)</a></span><ul class=\"toc-item\"><li><span><a href=\"#Semicolons\" data-toc-modified-id=\"Semicolons-4.1\">Semicolons</a></span></li><li><span><a href=\"#Blocks\" data-toc-modified-id=\"Blocks-4.2\">Blocks</a></span></li><li><span><a href=\"#Input-/-output\" data-toc-modified-id=\"Input-/-output-4.3\">Input / output</a></span></li></ul></li></ul></div>"
"<div class=\"toc\"><ul class=\"toc-item\"><li><span><a href=\"#About-the-choice-of-a-Jupyter-notebook\" data-toc-modified-id=\"About-the-choice-of-a-Jupyter-notebook-1\">About the choice of a Jupyter notebook</a></span></li><li><span><a href=\"#When-the-notebook-is-not-enough...\" data-toc-modified-id=\"When-the-notebook-is-not-enough...-2\">When the notebook is not enough...</a></span></li><li><span><a href=\"#Few-guidelines-about-Jupyter\" data-toc-modified-id=\"Few-guidelines-about-Jupyter-3\">Few guidelines about Jupyter</a></span><ul class=\"toc-item\"><li><span><a href=\"#Restarting-the-kernel\" data-toc-modified-id=\"Restarting-the-kernel-3.1\">Restarting the kernel</a></span></li></ul></li><li><span><a href=\"#Very-basic-C++-syntax-(in-notebook-and-in-general)\" data-toc-modified-id=\"Very-basic-C++-syntax-(in-notebook-and-in-general)-4\">Very basic C++ syntax (in notebook and in general)</a></span><ul class=\"toc-item\"><li><span><a href=\"#Semicolons\" data-toc-modified-id=\"Semicolons-4.1\">Semicolons</a></span></li><li><span><a href=\"#Blocks\" data-toc-modified-id=\"Blocks-4.2\">Blocks</a></span></li><li><span><a href=\"#Input-/-output\" data-toc-modified-id=\"Input-/-output-4.3\">Input / output</a></span></li><li><span><a href=\"#Comments\" data-toc-modified-id=\"Comments-4.4\">Comments</a></span></li></ul></li></ul></div>"
]
},
{
......@@ -242,6 +242,44 @@
"We will see that a bit more in detail in [a later chapter](/notebooks/1-ProceduralProgramming/6-Streams.ipynb), but printing something is really helpful early on hence this brief introduction here.\n"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### Comments\n",
"\n",
"There are two ways to comment code in C++:\n",
"\n",
"- `//` which comments all that is after this symbol on the same line\n",
"- `/*` ... `*/` which comments everything in the between the symbols.\n"
]
},
{
"cell_type": "code",
"execution_count": 14,
"metadata": {},
"outputs": [],
"source": [
"{\n",
" int i = 0; // Everything after // is commented until the end of the line\n",
"\n",
" /*\n",
"\n",
" commented...\n",
"\n",
" also commented...\n",
" */\n",
"\n",
" int j = 5; // no longer commented\n",
" \n",
" /*\n",
" \n",
" // This type of comment might be in the other style\n",
" \n",
" */\n",
"}"
]
},
{
"cell_type": "markdown",
"metadata": {},
......
%% Cell type:markdown id: tags:
# [Getting started in C++](/) - [Getting started with the tutorial](/notebooks/getting_started_with_tutorial.ipynb)
%% Cell type:markdown id: tags:
<h1>Table of contents<span class="tocSkip"></span></h1>
<div class="toc"><ul class="toc-item"><li><span><a href="#About-the-choice-of-a-Jupyter-notebook" data-toc-modified-id="About-the-choice-of-a-Jupyter-notebook-1">About the choice of a Jupyter notebook</a></span></li><li><span><a href="#When-the-notebook-is-not-enough..." data-toc-modified-id="When-the-notebook-is-not-enough...-2">When the notebook is not enough...</a></span></li><li><span><a href="#Few-guidelines-about-Jupyter" data-toc-modified-id="Few-guidelines-about-Jupyter-3">Few guidelines about Jupyter</a></span><ul class="toc-item"><li><span><a href="#Restarting-the-kernel" data-toc-modified-id="Restarting-the-kernel-3.1">Restarting the kernel</a></span></li></ul></li><li><span><a href="#Very-basic-C++-syntax-(in-notebook-and-in-general)" data-toc-modified-id="Very-basic-C++-syntax-(in-notebook-and-in-general)-4">Very basic C++ syntax (in notebook and in general)</a></span><ul class="toc-item"><li><span><a href="#Semicolons" data-toc-modified-id="Semicolons-4.1">Semicolons</a></span></li><li><span><a href="#Blocks" data-toc-modified-id="Blocks-4.2">Blocks</a></span></li><li><span><a href="#Input-/-output" data-toc-modified-id="Input-/-output-4.3">Input / output</a></span></li></ul></li></ul></div>
<div class="toc"><ul class="toc-item"><li><span><a href="#About-the-choice-of-a-Jupyter-notebook" data-toc-modified-id="About-the-choice-of-a-Jupyter-notebook-1">About the choice of a Jupyter notebook</a></span></li><li><span><a href="#When-the-notebook-is-not-enough..." data-toc-modified-id="When-the-notebook-is-not-enough...-2">When the notebook is not enough...</a></span></li><li><span><a href="#Few-guidelines-about-Jupyter" data-toc-modified-id="Few-guidelines-about-Jupyter-3">Few guidelines about Jupyter</a></span><ul class="toc-item"><li><span><a href="#Restarting-the-kernel" data-toc-modified-id="Restarting-the-kernel-3.1">Restarting the kernel</a></span></li></ul></li><li><span><a href="#Very-basic-C++-syntax-(in-notebook-and-in-general)" data-toc-modified-id="Very-basic-C++-syntax-(in-notebook-and-in-general)-4">Very basic C++ syntax (in notebook and in general)</a></span><ul class="toc-item"><li><span><a href="#Semicolons" data-toc-modified-id="Semicolons-4.1">Semicolons</a></span></li><li><span><a href="#Blocks" data-toc-modified-id="Blocks-4.2">Blocks</a></span></li><li><span><a href="#Input-/-output" data-toc-modified-id="Input-/-output-4.3">Input / output</a></span></li><li><span><a href="#Comments" data-toc-modified-id="Comments-4.4">Comments</a></span></li></ul></li></ul></div>
%% Cell type:markdown id: tags:
## About the choice of a Jupyter notebook
This notebook uses up [xeus-cling](https://xeus-cling.readthedocs.io/en/latest/), a special instance of Jupyter able to run C++ code based upon xeus (tool to build Jupyter kernels for any language) and cling (a creation from CERN to be able to run C++ as an interpreted language).
The reasons for these choices is to really access directly to handle C++ code without the hassle of explaining how to compile and run stuff, which is an especially cumbersome way to start with this (or any really...) language.
This is not to say this tutorial will ignore entirely these topics (see the dedicated [chapter](/notebooks/6-InRealEnvironment/0-main.ipynb), just that we will first focus on C++ code. However keep in mind that this notebook's fancy interpreter is not a typical C++ environment.
Jupyter Xeus-Cling is still under active development: you should really get a recent version and keep it up-to-date. Some examples in this lecture didn't work at first and were properly dealt with with a version one month later!
## When the notebook is not enough...
As we shall see repeatedly, Xeus-cling notebooks are far from being full-proof: some stuff that are perfectly acceptable C++ aren't accepted in them, and some others required work-arounds. When such an issue appears:
* It will be indicated explicitly in the notebook if a specific work around is used. We do not want you to take Jupyter work-arounds as a legit advice on how to write proper C++.
* If Jupyter can't deal with the code, we will use [Coliru](https://coliru.stacked-crooked.com/). Coliru is a C++ online compiler; others are listed [here](https://arne-mertz.de/2017/05/online-compilers/) ([Wandbox](https://wandbox.org/) deserves a shout out as it enables testing the same code with a great variety of compiler versions).
%% Cell type:markdown id: tags:
## Few guidelines about Jupyter
You might not be familiar with Jupyter notebooks, so here are few tips to run it smoothly (the _Help_ menu will help you find more if you need it).
In a Jupyter notebook the content is divided into _cells_, in our case we are using two kind of cells:
* Markdown cells, such as the ones into these very words are written.
* Code cells, which are running code. In these notebooks the chosen kernel is C++17, so the code is C++17 which is interpreted by cling.
There are two modes:
* Edit mode, in which you might change the content of a cell. In this mode the left part of the cell is in green.
* Command mode, in which you might take actions such as changing the type of a cell, create or delete a new one, etc...
To enter in edit mode, simply type on 'Enter'.
To enter in command mode, type 'Esc'.
To execute a cell, type 'Shift + Enter'. For a markdown cell it will edit nicely the content by interpreting the markdown, and for a code cell it will run the code.
In command mode, several handy shortcuts are there; I would recommend especially:
* `a` (add a cell above)
* `b` (add a cell below)
* `x` (cut a cell)
* `M` (change cell mode to Markdown)
The complete list is available in _Help_ > _Keyboard_ shortcut.
If for some reason the code in the notebook seems stuck, you might try to restart the kernel with one of the restart option in the _Kernel_ menu.
### Restarting the kernel
Sometimes something that should work doesn't... In this case try restarting the kernel: it might fix your issue!
%% Cell type:markdown id: tags:
## Very basic C++ syntax (in notebook and in general)
### Semicolons
In C++ most instructions end by a semicolon `;`. If you forget it, the underlying compiler doesn't understand the syntax.
%% Cell type:code id: tags:
``` C++17
{
int foo = 5 // COMPILATION ERROR!
}
```
%% Cell type:code id: tags:
``` C++17
{
int foo = 5; // OK
}
```
%% Cell type:markdown id: tags:
Spaces, end lines and tabulations act as word separators; utterly unreadable code as the one below is perfectly fine from the compiler standpoint:
%% Cell type:code id: tags:
``` C++17
# include <string>
{
int nombre ; nombre = 1
; std::string nom;
nom=
"truc" ;
nombre = 2
;
}
```
%% Cell type:markdown id: tags:
### Blocks
You may have notices the braces `{` and `}` in the examples above. They are here a technicality to make cling interpreter work better in a Jupyter environment, but that is also useful in a real C++ code.
What is between both braces constitute a **block**; variables that are initialized inside are destroyed once the closing brace is past (don't worry - we will come back to that [later](/notebooks/1-ProceduralProgramming/5-DynamicAllocation.ipynb#Stack)).
This is an incredibly useful feature: you may ensure this way that a variable is not kept any longer than necessary. We will come back to this feature (called the **locality of reference** later); let's see why they are useful in a notebook environment.
In C++, at a given scope a same variable can't be defined twice. So for instance if I defined twice a same variable, the compiler will yell about redefinition of a variable:
%% Cell type:code id: tags:
``` C++17
int i = 2; // Should be fine on the first call.
// But if you have executed it already, a new attempt will make the compiler yell.
```
%% Cell type:code id: tags:
``` C++17
int i = 1; // If the cell above was run, compilation error as `i` is already defined.
```
%% Cell type:markdown id: tags:
The only way to circumvent this is to restart the kernel... and you may then run only one of this cell, and only once.
So you might now see the usefulness of the braces: by putting them I define the variables in a cell in a block, and it is only defined inside this block. Same variable may this way be defined in different cells:
%% Cell type:code id: tags:
``` C++17
{
int i = 2; // Fine
}
```
%% Cell type:code id: tags:
``` C++17
{
int i = 1; // Also fine
}
```
%% Cell type:markdown id: tags:
### Input / output
Inputs and outputs aren't directly a part of the language itself, but are in the standard library (often abbreviated as STL for Standard Template Library even if some purist may yell and explain it's not 100 % the same thing...). You therefore need to __include__ a file named `iostream`; doing so will enable the use of the input / output facilities.
%% Cell type:code id: tags:
``` C++17
{
std::cout << "Hello world!" << std::endl; // Should fail (unless you run a cell that includes iostream before)
}
```
%% Cell type:code id: tags:
``` C++17
#include <iostream>
{
std::cout << "Hello world!" << std::endl; // Should work: std::cout and std::endl are now known.
}
```
%% Cell type:markdown id: tags:
- `std::cout` is the symbol to designate the standard output (i.e. your screen...)
- `std::endl` is the symbol to clean-up the stream and go to next line.
The operator `<<` is used to indicate what you direct toward the stream; here std::cout << "Hello world!" tells to redirect the string toward the standard output.
We will see that a bit more in detail in [a later chapter](/notebooks/1-ProceduralProgramming/6-Streams.ipynb), but printing something is really helpful early on hence this brief introduction here.
%% Cell type:markdown id: tags:
### Comments
There are two ways to comment code in C++:
- `//` which comments all that is after this symbol on the same line
- `/*` ... `*/` which comments everything in the between the symbols.
%% Cell type:code id: tags:
``` C++17
{
int i = 0; // Everything after // is commented until the end of the line
/*
commented...
also commented...
*/
int j = 5; // no longer commented
/*
// This type of comment might be in the other style
*/
}
```
%% Cell type:markdown id: tags:
© _CNRS 2016_ - _Inria 2018-2019_
_This notebook is an adaptation of a lecture prepared and redacted by David Chamont (CNRS) under the terms of the licence [Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)](http://creativecommons.org/licenses/by-nc-sa/4.0/)_
_The present version has been redacted by Sébastien Gilles and Vincent Rouvreau (Inria)_
......
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