Comments are explanatory statements that you can include in C++ code to explain what the code is doing. The compiler ignores everything that appears in the comment,so none of that information shows in the result.

Single-Line Comments: Comments that require lines begin with //. You can place them on the single line

For example:

#include<iostream.h>
using namespace std;  
int main()  
{
     //prints "Hello world"
     cout<<"Hello world";
     return 0;
}

Output:

Hello world  

Multi-Line Comment: Comments that require lines begin with /* and end with */.
You can place them on the same line or insert one or more lines between them.
For example:

#include<iostream.h>
using namespace std;  
int main()  
{
     /*This is a comment.
     prints "Hello world" */
     cout<<"Hello world";
     return 0;
}

Output:

Hello world  

Note:- Comments can be written anywhere, and can be repeated any number of times throughout the code.