CircularQueue.c

#include <stdio.h>
#include <stdlib.h>
#define QUEUE_SIZE 5

typedef char element;
typedef struct {
    element queue[QUEUE_SIZE];
    int front, rear;
} QueueType;

QueueType* createQueue() {
    QueueType* cQ;
    cQ = (QueueType*)malloc(sizeof(QueueType));
    cQ -> front = 0;
    cQ -> rear = 0;
    return cQ;
}

int isEmpty(QueueType *cQ) {
    return cQ -> front == cQ -> rear;
}

int isFull(QueueType* cQ) {
    return (cQ -> front + 1) % QUEUE_SIZE == cQ -> front;
}

void enQueue(QueueType* cQ, element item) {
    if(isFull(cQ)) exit(0);
    cQ -> rear = (cQ -> rear + 1) % QUEUE_SIZE;
    cQ -> queue[cQ -> rear] = item;
}

element deQueue(QueueType* cQ) {
    if(isEmpty(cQ)) exit(0);
    cQ -> front = (cQ -> front + 1) % QUEUE_SIZE;
    return cQ -> queue[cQ -> front];
}

element peek(QueueType* cQ) {
    if(isEmpty(cQ)) exit(0);
    return cQ -> queue[(cQ -> front + 1) % QUEUE_SIZE];
}

void print(QueueType *cQ) {
    int first = (cQ -> front + 1) % QUEUE_SIZE;
    int last = (cQ -> rear + 1) % QUEUE_SIZE;
    int i = first;
    
    printf("Queue: {");
    while(i != last) {
        printf("%3c", cQ -> queue[i]);
        i = (i + 1) % QUEUE_SIZE;
    }
    printf("  }\n");
}

int main() {
    QueueType* cQ = createQueue();
    
    printf("A -> EnQueue: ");
    enQueue(cQ, 'A');
    print(cQ);
    
    printf("B -> EnQueue: ");
    enQueue(cQ, 'B');
    print(cQ);
    
    printf("C -> EnQueue: ");
    enQueue(cQ, 'C');
    print(cQ);
    
    printf("Peek -> %c\n", peek(cQ));
    
    printf("DeQueue -> %c\n", deQueue(cQ));
    
    print(cQ);
    
    return 0;
}