Comments in C++

Let's say you worked hard and your sleepless nights brought you to Google but initially you have to go through the previous code base that has been written by other programmers. So to understand those million lines of code some description or important information is attached to understand the functionality of a specific block of code.

These important and self-explanatory blocks of information are called as comments.

What are comments?

While programming we require some blocks of code that the computer should not run and just ignore. These blocks are created by using comments.

We introduce comments by inserting two forward slashes // .

Let's see an example to demonstrate it.

#include <iostream>
using namespace std;

int main(){

  // This is a comment

  cout << "I am loving Learn Yards ";
  
  return 0;
}

Output :

I am loving Learn Yards

As you can notice, the "This is a comment" line is not being executed by the compiler and is just ignored.

You should definitely have one question : If it is not being read and executed by the computer , WHY are we using it ?

Comments are very useful for programmers, it is being used to add some important information or to annotate code for future reference. It is more like documenting your work in the code itself for the readability of the code for other fellow programmers.

Types of Comments

There are two types of Comments in C++:

1 . Single-Line Comment

As the name suggests, it is used to add comments on a single line. It is being added using //.

#include <iostream>
using namespace std;

int main(){

    // prints a string

    cout << "Marks " ;

    // prints a number

    cout << 78 ;

  return 0;
}

Output :

Marks 78

// prints a string
// prints a number

Both are single-line comments which are not being executed by the compiler.

2 . Multi-Line Comment

A multi-line comment occupies multiple lines of comments, it starts with /* and ends with */, but it cannot be nested.

Syntax 

/*
    Multiline Comment 
        .
        .
        .
        .
        .
        .
*/

Let's see with an example, how we can add multi-line comments in our code.

#include <iostream>
using namespace std;

int main(){

  /* This is a code
      to print the marks scored by 
      a student 
  */

  cout << "Marks " ;

  cout << 65 ;
  

  return 0;
}

Output :

Marks 65

Now let's predict the output of the code below :

#include <iostream>
using namespace std;

int main(){

  // This is a code
      to print the marks scored by 
      a student 
  

  cout << "Marks" ;

  cout << 65 ;
  

  return 0;
}

ERROR

This error occurred because we tried to add a multi-line comment using a // which is used to take a single line as a comment because of which these two lines are read by the compiler as a code, hence throwing an error.

"to print the marks scored by
a student"

Let's try another one.

#include <iostream>
using namespace std;

int main(){

  /*
    This is a comment
    /*
      This is a comment inside a comment
    */
  */

  cout << "Hey, there!";

  return 0;
}

Quiz

#include <iostream>
using namespace std;

  int main(){

    cout << comments ; // print the output

    return 0;
  }

#include <iostream>
using namespace std;

int main(){

  // cout << "Hello World";

  cout << 10;
  

  return 0;
}

Code without comments is like a book without a title; it leaves you guessing and lost in its pages.