虽然这里只使用了括号的计数，实现加减法则来配对括号。思想可以扩展：利用栈来实现括号的配对是十分简单的。

/*
** Check the pairing of braces in a C program.
*/

#include <stdio.h>
#include <stdlib.h>

int
main()
{
 int ch;
 int braces;

 braces = 0;

 /*
 ** Read the program character by character.
 */
 while( (ch = getchar()) != EOF ){
  /*
  ** Opening braces are always legal.
  */
  if( ch == ‘{‘ )
   braces += 1;

  /*
  ** A closing brace is legal only if matched to an
  ** opening brace.
  */
  if( ch == ‘}’ )
   if( braces == 0 )
    printf( “Extra closing brace!/n” );
   else
    braces -= 1;
 }

 /*
 ** No more input: make sure there aren’t any opening braces
 ** that were not matched.
 */
 if( braces > 0 )
  printf( “%d unmatched opening brace(s)!/n”, braces );

 return EXIT_SUCCESS;
}