queue_twostack.c

#include <stdio.h>
#define STACKSIZE 100

int stack_one[STACKSIZE];
int sp_one=-1;
void push_one(int item){
	stack_one[++sp_one]=item;
}
int pop_one(void){
	return stack_one[sp_one--];
}
int empty_one(void){
	return sp_one==-1;
}
int full_one(void){
	return sp_one==STACKSIZE-1;
}

int stack_two[STACKSIZE];
int sp_two=-1;
void push_two(int item){
	stack_two[++sp_two]=item;
}
int pop_two(void){
	return stack_two[sp_two--];
}
int empty_two(void){
	return sp_two==-1;
}
int full_two(void){
	return sp_two==STACKSIZE-1;
}

void enqueue(int item){
	if(full_queue()){
		printf("Full!\n");
		return;
	}
	if(!full_one())
		push_one(item);
	else{
		while(!full_two() && !empty_one())
			push_two(pop_one());
		push_one(item);
	}
}

int dequeue(void){
	int retval;
	if(empty_two()){
		while(!empty_one()){
			retval=pop_one();
			push_two(retval);
		}
	}
	if(empty_two()){
		printf("Queue empty.\n");
		return -1;
	}else
		retval=pop_two();
	return retval;
}

int empty_queue(){
	return empty_one() && empty_two();
}

int full_queue(){
	return full_one() && full_two();
}

int main(int argc, char const *argv[])
{
	int data[]={1,2,3,4,5,6,7,8,9,10};
	int size=sizeof(data)/sizeof(int);
	int i=0;
	while(i<6)
		enqueue(data[i++]);
	while(!empty_queue())
		printf("%d\n",dequeue());
	while(i<size)
		enqueue(data[i++]);
	while(!empty_queue())
		printf("%d\n",dequeue());
	return 0;
}