Queue in C : Queue « Data Structure Algorithm « C / ANSI-C

1. C / ANSI-C
2. Data Structure Algorithm
3. Queue

Queue in C

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

#define MAX 100

char *p[MAX], *pop(void);
int spos = 0;
int rpos = 0;
void add(void), push(char *q), print(void), remove(void);


void add(void)
{
  char s[256], *p;

  do {
    printf("spos %d: ", spos+1);
    gets(s);
    if(*s==0) {
       break;
    }
    p = (char *) malloc(strlen(s)+1);
    if(!p) {
      printf("Out of memory.\n");
      return;
    }
    strcpy(p, s);
    if(*s) {
       push(p);
    }
  } while(*s);
}

void print(void)
{
  int t;

  for(t=rpos; t < spos; ++t)
    printf("%d. %s\n", t+1, p[t]);
}

void remove(void)
{
  char *p;

  if((p=pop())==NULL) {
     return;
  }
  printf("%s\n", p);
}

void push(char *q)
{
  if(spos==MAX) {
    printf("List Full\n");
    return;
  }
  p[spos] = q;
  spos++;
}

char *pop(void)
{
  if(rpos==spos) {
    printf("No more.\n");
    return NULL;
  }
  rpos++;
  return p[rpos-1];
}

int main(void)
{
  char s[80];
  register int t;

  for(t=0; t < MAX; ++t) {
     p[t] = NULL;
  }

  while(1) {
    printf("Add(A), Print(P), Remove(R), Quit(Q): ");
    gets(s);
    *s = toupper(*s);

    switch(*s) {
      case 'A':
        add();
        break;
      case 'P':
        print();
        break;
      case 'R':
        remove();
        break;
      case 'Q':
        exit(0);
    }
  }
  return 0;
}

           
       

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