函数不返回

Question

struct m_queue{
       int ndata;
       struct m_queue* pnext;
       struct m_queue* pdown;
       };

 int search(struct m_queue* list,int key){  //returns the index where it founded the key, return -1 if key is not found
        struct m_queue* temp;//searches horizontal
        struct m_queue* run;//searches downward
        int i;
        temp = list;

        run = temp->pdown;

        getch();
        while(temp!=NULL){

            getch();
            while(run!=NULL){
                if(run->ndata == key)
                    return temp->ndata;
                else
                    run = run->pdown;
            }
            temp = temp->pnext;
            run = temp->pdown;

        }
        printf("returning -1");
        getch();
        return -1;

    }

i checked the other functions already and i'm pretty sure there's no flaw but whenever i debug my program it always highlight the segment "run = temp->pdown". this functions doesn't return -1 it just return if it found the key. this was coded in c language

Answer 1

If temp is NULL , run = temp->pdown; is an invalid operation.

}
temp = temp->pnext;
if (temp!=NULL)  //add this line
    run = temp->pdown;

Answer 2

The problem lies in these lines:

      temp = temp->pnext;
      run = temp->pdown;

what happens when temp is NULL? You are trying to access temp->pdown without checking whether temp is NULL.

Answer 3

   //run = temp->pdown;                    //this statement not needed

    getch();
    while(temp!=NULL){
        run = temp->pdown;                 //add this statement
        getch();
        while(run!=NULL){
            if(run->ndata == key) 
               return temp->ndata;
            else
                run = run->pdown;
        }
        temp = temp->pnext;
       // run = temp->pdown;              // this statement not needed
  }

make this change to avoid accessing temp when it is NULL.