A computer is designed to follow instructions and commands. Typically, these instructions are organized into a file that the computer follows and executes. These formatted instructions are known as code. Essentially, code is a set of commands given to a computer to execute.
When reading a file of code, the computer goes through each line and executes every command one at a time in order.
The basic skeleton of a C++ file will resemble the following:
<span id="L1" class="line"><span class="k">using</span> <span class="k">namespace</span> <span class="n">std</span><span class="p">;</span></span>
<span id="L2" class="line"></span>
<span id="L3" class="line"><span class="kt">int</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span></span>
<span id="L4" class="line"> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span></span>
<span id="L5" class="line"><span class="p">}</span></span>In C++, each component of this skeleton is required in order for the code to properly run.
Libraries
There are files that store all the possible instructions C++ could recognize. All the commands that the computer understands and could execute are placed in a file called a library. A library stores a list of commands that the computer could follow. If a computer has access to a library, it could perform any command that is listed in that library.
The most common library that is used when coding a C++ file is the standard library.
For beginner purposes, all commands that will be used when coding will be in the standard library.
To tell the computer that a file will use the standard library, using namespace std; is placed at the beginning of the file.
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Note
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Always include libraries at the beginning of a C++ file. |
The Main Function
When a computer first runs a code file, it will go down each line of
code until it reaches a line with int main(). This line is referred to
as the main function. Once the computer finds the main function, it
will begin executing all commands listed inside the braces ({}). Any
commands that are in the file must be placed within the main function.
<span id="L1" class="line"><span class="kt">int</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span></span>
<span id="L2" class="line"> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span></span>
<span id="L3" class="line"><span class="p">}</span></span>The computer reads and executes each line of code in the main function
and ends once it has reached the line return 0;. Any line of code that
follows this line will be ignored. A C++ file should always have
return 0; within its main function.
Whitespace
Whitespace is any part of a file that is intentionally left blank. This includes spaces, indents, and empty lines. Unlike some other computing languages (e.g. Python), the amount of whitespace that is left in a C++ file has no effect on the computer’s performance when it is executing the code. So both of the following examples are identical:
<span id="L1" class="line"><span class="k">using</span> <span class="k">namespace</span> <span class="n">std</span><span class="p">;</span></span>
<span id="L2" class="line"></span>
<span id="L3" class="line"><span class="kt">int</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span></span>
<span id="L4" class="line"> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span></span>
<span id="L5" class="line"><span class="p">}</span></span><span id="L1" class="line"><span class="k">using</span> <span class="k">namespace</span></span>
<span id="L2" class="line"><span class="n">std</span><span class="p">;</span></span>
<span id="L3" class="line"><span class="kt">int</span></span>
<span id="L4" class="line"><span class="n">main</span><span class="p">(){</span><span class="k">return</span> <span class="mi">0</span><span class="p">;}</span></span>Though not required, it is encouraged to develop a habit of using whitespace in order to make a C++ file easier to read. This includes indenting any commands that are within the main function.
Comments
Apart from having computers skip over any whitespace, the computer could also be told to skip any text in a file while executing the code. A comment is any text in a file that is not meant for the computer to read. Users put important information about the file into the code as comments. Overall, comments makes code more readable for humans.
<span id="L1" class="line"><span class="k">using</span> <span class="k">namespace</span> <span class="n">std</span><span class="p">;</span></span>
<span id="L2" class="line"><span class="kt">int</span> <span class="n">main</span><span class="p">(){</span></span>
<span id="L3" class="line"> <span class="c1">// This is a comment.</span></span>
<span id="L4" class="line"> <span class="cm">/*</span></span>
<span id="L5" class="line"><span class="cm"> Everything between the</span></span>
<span id="L6" class="line"><span class="cm"> 2 symbols are comments.</span></span>
<span id="L7" class="line"><span class="cm"> */</span></span>
<span id="L8" class="line"> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span></span>
<span id="L9" class="line"><span class="p">}</span></span>There are two main methods for adding comments into a C++ file. Adding
// will have the computer skip all remaining text in a line of code.
All text that is enclosed by /* and */ are commented out and not
read by the computer.
In Summary
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A library is a file that stores a list of commands that a computer can do
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using namespace std;makes your computer able to use the standard library -
All code must be placed in the main function
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return 0;should always be placed at the end of the main function -
Whitespaces are any spaces, indents, and empty lines
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Whitespace is used to organize code to make it more readable
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Comments can be used to add remarks/explanation about the code