basic operations for the stack
setstack(ps)
/* Sets stack s to empty */
stack *ps;
{
(*ps).top = -1;
}
empty(ps)
/* Returns true only if
stack s is empty.
*/
stack *ps;
{
return((*ps).top == -1);
}
push(value,ps)
/* Inserts contents of value as
top entry of stack s.
*/
whatever value;
stack *ps;
{
if ((*ps).top == (LIMIT - 1))
overflow(ps);
else
{
(*ps).top = (*ps).top + 1;
(*ps).stackarray[(*ps).top] = value;
}
}
pop(ps,pvalue)
/* Removes the top entry of stack s
and places its contents in value.
*/
stack *ps;
whatever *pvalue;
{
if (empty(ps))
underflow(ps);
else
{
*pvalue = (*ps).stackarray[(*ps).top];
(*ps).top = (*ps).top - 1;
}
}
overflow(ps)
/* Prints a message when
the stack overflows.
*/
stack *ps;
{
printf("\n stack overflow \n");
}
underflow(ps)
/* Prints a message when
the stack underflows.
*/
stack *ps;
{
printf("\n stack underflow \n");