Comments

The C language supports block comments.

Comments should be used in program code to document the program. This is to explain the neat but esoteric aspects of the program, not only to the programmer himself, but to any successors who find themselves needing to understand the code. Good comments don't repeat the code, they explain it; comments may tell why something is being done, or why it is being done this way. They may summarize the effect of a subprogram.  A compiler treats the content of a comment as if it were not there.

Syntactically, C treats comments as token separators or "white space."  Comments are otherwise ignored by the compiler.

Comments can span lines.

comment

Comments have no meaning to the compiler or to the program. Comments are only for people who read the source code.

• C comments cannot be nested: that is,
  /* This is an outer comment
  /* and this is an illegal nested comment */
  The compiler will interpret this line as outside of a comment */
• Some C compilers do allow nested comments, but this is a non-portable extension. 
• Microsoft® C compilers also allow C++ comment syntax,
  // .∗ EOL
  but this is a non-portable extension. 
• End of line comments ('//') should never be used in preprocessor macro #define statements. 

/* Comments can be on a single line */
/*
      Comments can also 
      span multiple lines.
*/
     x = 4; /* Comments should explain the code, not repeat it. */