A block is a compound statement.  It allows more than one statement
  to appear where a single statement ordinarily is used.  It is made
  up of a list of declarations and statements, enclosed in braces:

           { [declaration ...] [statement ...] }

  The declaration list is optional; if it is included, all
  declarations of variables are local to the block and supersede
  previous declarations for the duration of the block.  A block is
  entered normally when control flows into it, or when a goto
  statement transfers control to a label at the beginning of the
  block.  Each time the block is entered normally, storage is
  allocated for auto or register variables.  If, on the other hand, a
  goto statement transfers control to a label inside the block or if
  the block is the body of a switch statement, these storage
  allocations do not occur.  Blocks can be used wherever single
  statements are valid -- for example, as the action clause of an if
  statement:

            if ( i < 1 )
               {                       /* BEGINNING OF BLOCK */
                  char x;
                  for (x = 'a';  x <= 'z';  x++)
                     printf("char = %c\n", x);
               }                       /* END OF BLOCK      */