four06% cat -n scan.c
     1	/* scan.c: scanner implementation.
     2	 * Recognizes C-type comments
     3	 * Based on a finite-state automaton.
     4	 * Uses gotos for implementation.
     5	 */
     6	#include <stdio.h>
     7	#include <string.h>
     8	#include <stdlib.h>
     9	#include "scan.h"
    10	char * makestr(char ch);
    11	void scan(char *s)
    12	{
    13	
    14	   char ch;
    15	   strcpy(s, "/*");
    16	
    17	
    18	   L0: ch = getchar();
    19	      if (ch == '/') goto L1;
    20	      else goto L0;
    21	   L1: ch = getchar();
    22	      if (ch == '*') goto L2;
    23	      else goto L0;
    24	   L2: ch = getchar();
    25	      strcat(s, makestr(ch));
    26	      if (ch == '*') goto L3;
    27	      else goto L2;
    28	   L3: ch = getchar();
    29	      strcat(s, makestr(ch));
    30	      if (ch == '*') goto L3;
    31	      else if (ch == '/') goto L4;
    32	      else goto L2;
    33	   L4: return;
    34	}
    35	
    36	
    37	/* makestr: convert a char to a string */
    38	char *makestr(char ch)
    39	{
    40	   char *r = (char *) malloc(2);
    41	   r[0] = ch;
    42	   r[1] = '\0';
    43	   return r;
    44	}
four06% cat -n scan.h
     1	/* scan.h: scanner header file */
     2	void scan(char *s);
four06% cat -n comment.c
     1	/* comment.c: driver to test comment scanner */
     2	#include <stdio.h>
     3	#include <string.h>
     4	#include "scan.h"
     5 void main(void)
     6	{
     7	   char s[50];
     8	   for ( ; ; ) {
     9	      scan(s);
    10	      printf("Next comment:\"%s\"\n", s);
    11	      if (strcmp(s, "/*quit*/") == 0) break;
    12	   }
    13	}
four06% cat -n scan2.c
     1	/* scan2.c: scanner implementation.
     2	 * Recognizes C-type comments
     3	 * Based on a finite-state automaton.
     4	 * No gotos in this version, but state variable instead.
     5	 */
     6	#include <stdio.h>
     7	#include <string.h>
     8	#include <stdlib.h>
     9	#include "scan.h"
    10	char * makestr(char ch);
    11	void scan(char *s)
    12	{
    13	   int state = 0;
    14	   char ch;
    15	   strcpy(s, "/*");
    16	   while (state != 4) {
    17	      switch (state) {
    18	      case 0: ch = getchar();
    19	              if (ch == '/') state = 1;
    20	              else state = 0; break;
    21	      case 1: ch = getchar();
    22	              if (ch == '*') state = 2;
    23	              else state = 0; break;
    24	      case 2: ch = getchar();
    25	              strcat(s, makestr(ch));
    26	              if (ch == '*') state = 3;
    27	              else state = 2; break;
    28	      case 3: ch = getchar();
    29	              strcat(s, makestr(ch));
    30	              if (ch == '*') state = 3;
    31	              else if (ch == '/') state = 4;
    32	              else state = 2; break;
    33	      case 4: return; break;
    34	      } /* end of switch */
    35	   } /* end of while */
    36	}
    37	/* makestr: convert a char to a string */
    38	char *makestr(char ch)
    39	{
    40	   char *r = (char *) malloc(2);
    41	   r[0] = ch;
    42	   r[1] = '\0';
    43	   return r;
    44	}
four06% cc -o comment2 comment.c scan2.c
four06% cat comment.source
 x = 47 / 13 * 12; /**/
 /***/ /****/ /*/ ?? * / */
 /* abc; */    /* over
  two lines */ JUNK! 3.14159; /*quit*/
four06% comment2 < comment.source
Next comment:"/**/"
Next comment:"/***/"
Next comment:"/****/"
Next comment:"/*/ ?? * / */"
Next comment:"/* abc; */"
Next comment:"/* over
  two lines */"
Next comment:"/*quit*/"