Thread: Stacks

Code:

#define SIZE 10

struct student 
{
    int id;
    char surname[20];
};

struct stack
{
    struct student array[SIZE];
    int top;
};

from the above data structures i need to implement the following:-
1. void initialise(struct stack *s);
2. int full(struct stack *s);
3. struct student *pop(struct stack *s);


Please check if it below is correct:-

Code:

void initialise(struct stack *s)
{
    s->top == -1;
}

int full(struct stack *s)
{
    return(s->top == SIZE - 1);
}

/*im not confident if the function below is right*/
struct student *pop(struct stack *s)
{
    if(empty(s))
    {
        fprintf(stderr, "Stack underflow\n");
        exit(1);
     }
     return &s->array[(s->top)--];
}

Please advice. Thank you
-hermit-

hmm...got abit de-railed there, that wasnt my question. I wanted to know if the pop function is ok?

Sorry that was a typo, you are right it should be:-

Code:

{
 .....
     if(empty(s))
     {
        fprintf(stderr, "stack underflow\n");
        exit(1);
     }
}

Not really, as the non-pointer version creates a copy.

Lets, say that STACK is implemented as dynamic linked list. Below are the stuctures:-

Code:

struct student
{
     int id;
     char surname[20];
};

struct data
{
    struct student *stud;
    struct data *next;
};

struct stack
{
    struct data *top;
    int size;
};

how would i write the following functions?

void initialise(struct stack *s);
struct student *stack_top(struct stack *s);
struct student *pop(struct stack *s);

let me take a guess? Im abit confused with this one:-

Code:

void initialise(struct stack *s)
{
      s->top == NULL;
      s->size = -1;
}

Really need some help here.... thank you guys

what about the other two functions?

Code:

struct student *stack_top(struct stack *s)
{
      if(s->top == NULL)
           return NULL;

     return (s->top->stud);
}

Please advice. THANKS

Code:

struct student *pop(struct stack *s)
{ 
        struct student *student;    
        struct data * data;  
  
        student = stack_top(s);  
  
       if (student == NULL)  
      {  
         ....  
      }  
       data = s->top;     
       s->top = data->next;  
       free(data);  
       return student;  
}

i have worked it out too