#define SLIMIT 20

typedef int whatever;

typedef struct

{

whatever stackarray[SLIMIT?];

int top;

}stack;

setstack(ps)

/* Sets stack s to empty. */

stack *ps;

{

(*ps).top = ?;

}

empty(ps)

/* Returns true only if stack s is empty. */

stack *ps;

{

return((*ps).top == -1);

}

push(value,ps)

/* Inserts contents of value as

the top entry on stack s.

/*

whatever value;

stack *ps;

{

if((*ps).top == (SLIMIT-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 copies its contents into value.

*/

stack *ps;

whatever *pvalue;

{

if(empty(ps))

underflow(ps);

else

{

*pvalue = (*ps).stackarray[(*ps).top];

(*ps).top = (*ps).top - 1;

}

}

whatever item(i,ps)

/* Returns a copy of the ith

entry in stack s. When i is

zero it returns a copy of

the top entry.

*/

stack *ps;

{

return((*ps).stackarray[(*ps).top-i]);

}

overflow(ps)

/* Prints a message if the stack overflows. */

stack *ps;

{

printf("\n stack overflow ");

}