C Pocket Reference

Block and Expression Statements

A block , also called a compound statement, groups a number of statements together into one statement. A block can also contain declarations.

The syntax for a block is:

{[list of declarations][list of statements]}

Here is an example of a block:

{ int i = 0;      /* Declarations  */
  static long a;
  extern long max;

  ++a;            /* Statements    */
  if( a >= max)
  {   . . .    }  /* A nested block */
  . . .
}

The declarations in a block normally precede the statements. However, ANSI C99 permits free placement of declarations.

New blocks can occur anywhere within a function block. Usually a block is formed wherever the syntax calls for a statement, but the program requires several statements. This is the case, for example, when more than one statement is to be repeated in a loop.

An expression statement is an expression followed by a semicolon. The syntax is:

[expression] ;

Here is an example of an expression statement:

 y = x;        // Assignment

The expression—an assignment or function call, for example—is evaluated for its side effects. The type and value of the expression are discarded.

A statement consisting only of a semicolon is called an empty statement , and does not peform any operation. For example:

for ( i = 0;  str[i] != '\0'; ++i )
   ;                     // Empty statement