C/Data Structure Algorithm/Queue
A circular queue example using a keyboard buffer
/*
C: The Complete Reference, 4th Ed. (Paperback)
by Herbert Schildt
ISBN: 0072121246
Publisher: McGraw-Hill Osborne Media; 4 edition (April 26, 2000)
*/
/* A circular queue example using a keyboard buffer. */
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#define MAX 80
char buf[MAX+1];
int spos = 0;
int rpos = 0;
void qstore(char q);
char qretrieve(void);
int main(void)
{
register char ch;
int t;
buf[80] = "\0";
/* Input characters until a carriage return is typed. */
for(ch=" ",t=0; t<32000 && ch!="\r"; ++t) {
if(_kbhit()) {
ch = _getch();
qstore(ch);
}
printf("%d ", t);
if(ch == "\r") {
/* Display and empty the key buffer. */
printf("\n");
while((ch=qretrieve()) != "\0") printf("%c", ch);
printf("\n");
}
}
return 0;
}
/* Store characters in the queue. */
void qstore(char q)
{
if(spos+1==rpos || (spos+1==MAX && !rpos)) {
printf("List Full\n");
return;
}
buf[spos] = q;
spos++;
if(spos==MAX) spos = 0; /* loop back */
}
/* Retrieve a character. */
char qretrieve(void)
{
if(rpos==MAX) rpos = 0; /* loop back */
if(rpos==spos) return "\0";
rpos++;
return buf[rpos-1];
}
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;
}