How to add comments in C++

By Ranjeet V

This tutorial will teach you how to add comments in your C++ program. Comments are used in a program to explain the code. Comments have no real effect on your program. The compiler ignores the comments and does not process it.

Add Comments in C++

There are two types of comment in C++:

• Single line comment
• Multi-line comment

How to add single line comment in C++: 

To add single line comment in your program, you can use //. The compiler ignores everything that comes in the line after //.

see the code below.

#include <iostream>
using namespace std;

int main()
{
  printf("Codespeedy.");  //prints Codespeedy
  return 0;
}

The output of the above code will be:

Codespeedy.

Now if we remove //prints Codespeedy, there’ll be no change in the output as you can see here.

#include <iostream>
using namespace std;

int main()
{
  printf("Codespeedy.");  
  return 0;
}

Output:

Codespeedy

How to add a multi-line comment in C++:

To add a multi-line comment in a C++ program, use /* and */.
/* is used where the multi-line comment starts and */ is used where the comment ends. See the code for a better understanding.

#include <iostream>
using namespace std;

int main()
{
  printf("Codespeedy.");  
  /*It
        prints
  Codespeedy.*/
  return 0;
}

The output of this code is:

Codespeedy.

Here you can see that as soon as the compiler encounters a /* symbol, it ignores everything until it reaches a */ symbol.

Now, if we remove /* and */ symbols and everything between it, It will still print Codespeedy.

#include <iostream>
using namespace std;

int main()
{
  printf("Codespeedy.");  
  
  return 0;
}

Now the output is:

Codespeedy.

We can use /* and */ for a single line comment as well. See the example code.

#include <iostream>
using namespace std;

int main()
{
  printf("Codespeedy.");    /*prints Codespeedy.*/
  return 0;
}

Output:

Codespeedy.

Nested Comments:

If you use nested comments in your C++ program, chances are that it might show an error. Let’s take a look at this example.

#include <iostream>
using namespace std;
int main()
{
  printf("Codespeedy.");  
  /*prints
  /*nested
  comment*/
  Codespeedy.*/
  return 0;
}

Now your compiler will throw an error because it does not consider the 9th line ( Codespeedy*/) a comment. The key point here is that the comment starts when it encounters a /* symbol which is in the 6th line and ends as soon as it finds a */ symbol which is in the 8th line of code. Thus the comment ends there and since there is no /* symbol afterwards, the next statement is not considered a comment. Hence an error is thrown by the compiler.

Therefore the use of nested comments should be avoided in C++.

Also read:

• An Overview of C++ Programming Language
• Command Line Arguments in C++