数据结构链式栈进栈出栈代码

以下是链式栈的进栈和出栈代码：

#define datatype int

typedef struct stacknode {
    datatype data;
    struct stacknode *pNext;
} StackNode;

StackNode *init(StackNode *phead) {
    phead = (StackNode *)malloc(sizeof(StackNode));
    phead->pNext = NULL;
    return phead;
}

int isEmpty(StackNode *phead) {
    if (phead->pNext == NULL) {
        return 1;
    }
    else {
        return 0;
    }
}

StackNode *push(StackNode *phead, datatype data) {
    StackNode *pnew = (StackNode *)malloc(sizeof(StackNode));
    pnew->data = data;
    pnew->pNext = phead->pNext;
    phead->pNext = pnew;
    return phead;
}

StackNode *pop(StackNode *phead, datatype *data) {
    if (isEmpty(phead)) {
        printf("The stack is empty!\n");
        return phead;
    }
    else {
        StackNode *ptemp = phead->pNext;
        *data = ptemp->data;
        phead->pNext = ptemp->pNext;
        free(ptemp);
        return phead;
    }
}