没有错误，但是当我执行它时，它显示 a.exe 没有运行

Question

I made a queue ADT program, and it has no error, but when I run this code, it shows that a.exe has stopped working. I use Windows 7 with i5 processor. Please explain the problem.

Here is the code:

#include<stdio.h>
#include<stdlib.h>

typedef struct node_info
{
    void*dataptr;
    struct node_info*next;
}node;

typedef struct 
{
    node* f;
    node* r;
    int count;
}queue;

queue*createq()
{
    queue*qp;
    qp=(queue*)malloc(sizeof(queue));
    if(!qp)
        return NULL;
    qp->count=0;
    qp->f=NULL;
    qp->r=NULL;
    return qp;
}

int enq(queue*qp,void*data)
{
    node*temp;
    temp=(node*)malloc(sizeof(node));
    if(!temp)
        return 0;
    temp->dataptr=data;
    temp->next=NULL;
    if(qp->count==0)
        qp->f=temp;
    else
        qp->r->next=temp;
    qp->r=temp;
    (qp->count)++;
    return 1;
}

void*deq(queue*qp)
{
    if(qp->count==0)
        return 0;
   node*temp;
   void*dout;
   temp=qp->f;
   dout=temp->dataptr;
   qp->f=temp->next;
   if(qp->count==1)
        qp->r=NULL;
    (qp->count)--;
    return dout;
}

void displayq(queue*qp)
{
    node*temp=qp->f;
    if(qp->count==0)
        printf("queue is empty");
    else
    { 
        printf("%d",*(int*)temp->dataptr);
        temp=temp->next;
    }
}

int main (queue*qp)
{
    int ele,choice;
    printf("\nEnter\n1.enqueue\n2.dequeue\n3.display\n\n");
    scanf("%d",&choice);
    while(1)
    {
        switch(choice)
        {
            case 1: 
                printf("enter the element to insert\n");
                scanf("%d",&ele);
                if(enq(qp,&ele))
                printf("%d has been inserted",*(int*)qp->r->dataptr);
                else
                printf("element not inserted");
            case 2:
                if(qp->count==0)
                printf("queue is empty");
                printf("%d is removed",*(int*)(deq(qp)));
            case 3:
                displayq(qp);
        } 
    }
}

Here is a screenshot

Answer 1

Incorrect definition of main

The compiler did emit meaningful warnings, but you decided to ignore them.

Unless this declaration,

int main(queue *qp)

is provided and documented by a certain implementation, it is invalid.

---

From C11:

The function called at program startup is named main. The implementation declares no prototype for this function. It shall be defined with a return type of int and with no parameters:

int main (void) { /* ... */ }

or with two parameters (referred to here as argc and argv, though any names may be used, as they are local to the function in which they are declared):

int main (int argc, char *argv[]) { /* ... */ }

or equivalent; or in some other implementation-defined manner.

---

Always compile with warnings enabled, and consider warnings as errors.

---

To cast or not to cast?

Regarding casting the result of malloc and family:

It is redundant and might hide a bug. These functions returns a generic void pointer, or void * , that is automatically promoted to the correct type.

---

Fall-through:

Every case in a switch requires a break statement or you risk fall-through. (Assuming fall-through is not intentional)

From C11:

6.8.6.3 The break statement

Constraints

1 A break statement shall appear only in or as a switch body or loop body.

Semantics

2 A break statement terminates execution of the smallest enclosing switch or iteration statement.

---

scanf() returns a value:

scanf() returns the number of elements it has successfully processed and converted. You should check if it succeeded.

Aside: Space-bar makes for readability, use it. As is, your code is unreadable and it's hard to decipher where a potential bug might be.