我在c中创建了双队列(deque)，我要求用户输入操作代码来执行以下操作，直到他/她想要。: -
- enque_from_back
- deque_from_front
- enque_from_front
- deque_from_back
所有的函数都工作得很好，但是当我调用deque_from_back()程序立即退出。我没有发现发生这种情况的原因。
请参见deque_from_back()函数
// Implementation of double queue using linked list.
#include<stdio.h>
#include<stdlib.h>
typedef struct Queue Queue;
struct Queue{
int data;
Queue *next;
};
typedef enum STATUS STATUS;
enum STATUS {FAILED, SUCCESS, MEMFAILED, UNDER_FLOW};
// Prototype declaration
STATUS enque_from_back(Queue **front,Queue **rear,int val);
void deque_from_front(Queue **front);
STATUS enque_from_front(Queue **front,Queue **rear,int val);
void deque_from_back(Queue ** , Queue **);
void display(Queue *q);
void menu();
// Driver Code
int main(){
Queue *front = NULL, *rear = NULL;
int num,opr_cd;
STATUS flag;
while(opr_cd != 4){
printf("n------------------------------------------------------------------");
menu();
printf("nchoose an option : ");
scanf("%d",&opr_cd);
if(opr_cd < 0 || opr_cd > 5){
printf("nEnter valid operation code.");
continue;
}
// inserting data from end
else if(opr_cd == 1){
printf("nEnter number to enque from back : ");
scanf("%d",&num);
flag = enque_from_back(&front,&rear,num);
if(flag == MEMFAILED) puts("Memory Failed...n");
else printf("%d enqued to end.n",num);
}
// inserting data from start
else if(opr_cd == 3){
printf("nEnter number to enque from start : ");
scanf("%d",&num);
flag = enque_from_front(&front,&rear,num);
if(flag == MEMFAILED) puts("Memory Failed...n");
else printf("%d enqued to start.n",num);
}
// deque data from start
else if(opr_cd == 2){
if(front == NULL){
printf("nQueue is underflow nothing to delete.");
continue;
}
num = front->data;
deque_from_front(&front);
printf("n%d removed from queue",num);
}
// deque data from end
else if(opr_cd == 4){
num = rear->data;
if(front == NULL){
printf("nQueue is underflow nothing to delete.");
continue;
}
deque_from_back(&front,&rear);
printf("n%d removed from queue",num);
}
// displaying data in queue
else if(opr_cd == 5){
display(front);
}
else if(opr_cd == 0){
printf("ntEXITTED PROGRAM....");
return 0;
}
}
return 0;
}
// function to insert item in queue from end
STATUS enque_from_back(Queue **front,Queue **rear,int val){
Queue *tem_queue = (Queue*)malloc(sizeof(Queue));
if(tem_queue == NULL)
return MEMFAILED;
tem_queue->data = val;
tem_queue->next = NULL;
if(*front == NULL)
*front = tem_queue;
else
(*rear)->next = tem_queue;
*rear = tem_queue;
return SUCCESS;
}
// function to insert item in queue from start
STATUS enque_from_front(Queue **front,Queue **rear,int val){
Queue *tem_node = (Queue*)malloc(sizeof(Queue));
if(tem_node == NULL)
return MEMFAILED;
tem_node->data = val;
tem_node->next = *front;
if(*rear == NULL)
*rear = tem_node;
*front = tem_node;
return SUCCESS;
}
//function to delete data from start
void deque_from_front(Queue **front){
Queue *tem_front = *front;
*front = tem_front->next;
free(tem_front);
}
// function to delete from end
void deque_from_back(Queue **front, Queue **last){
Queue *sec_last;
Queue *node_to_delete = *front;
while (node_to_delete->next != NULL){
sec_last = node_to_delete;
node_to_delete = node_to_delete->next;
}
sec_last->next = NULL;
*last = sec_last;
free(node_to_delete);
}
//function to display item in queue.
void display(Queue *q){
if(q == NULL){
printf("nQueue is empty nothing to display");
return;
}
printf("Data in Queue :nn");
for(; q != NULL ; q = q->next)
printf("%d ",q->data);
}
// function to show menu
void menu(){
printf("nn+-------------------------------+n| MENU |n|-------------------------------|n| press 1 -> ENQUE |n| press 2 -> DEQUE |n| press 3 -> ENQUE FROM START |n| press 4 -> DEQUE FROM END |n| press 5 -> DISPLAY QUEUE |n| press 0 -> EXIT |n+-------------------------------+nn");
}
查看您的while条件:while(opr_cd != 4)
选择deque_from_back时。opr_cd变为4。因此它退出程序。
条件应为while(opr_cd!=0)