073.队列实例

#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>
#define MAX 100
char *p[MAX], *qretrieve(void);
int spos = 0;
int rpos = 0;
void enter(void), qstore(char *q), review(void), delete_ap(void);
int main(void)
{
  char s[80];
  register int t;
  for(t=0; t < MAX; ++t) p[t] = NULL; /* init array to nulls */
  for(;;) {
    printf("Enter, List, Remove, Quit: ");
    gets(s);
    *s = toupper(*s);
    switch(*s) {
    case 'E':
      enter();
      break;
    case 'L':
      review();
      break;
    case 'R':
      delete_ap();
      break;
    case 'Q':
      exit(0);
    }
  }
  return 0;
}
/* Enter appointments in queue. */
void enter(void)
{
  char s[256], *p;
  do {
    printf("Enter appointment %d: ", spos+1);
    gets(s);
    if(*s==0) break; /* no entry */
    p = (char *) malloc(strlen(s)+1);
    if(!p) {
      printf("Out of memory.\n");
      return;
    }
    strcpy(p, s);
    if(*s) qstore(p);
  } while(*s);
}
/* See what's in the queue. */
void review(void)
{
  register int t;
  for(t=rpos; t < spos; ++t)
    printf("%d. %s\n", t+1, p[t]);
}
/* Delete an appointment from the queue. */
void delete_ap(void)
{
  char *p;
  if((p=qretrieve())==NULL) return;
  printf("%s\n", p);
}
/* Store an appointment. */
void qstore(char *q)
{
  if(spos==MAX) {
    printf("List Full\n");
    return;
  }
  p[spos] = q;
  spos++;
}
/* Retrieve an appointment. */
char *qretrieve(void)
{
  if(rpos==spos) {
    printf("No more appointments.\n");
    return NULL;
  }
  rpos++;
  return p[rpos-1];
}