If we attempt to pop an empty stack, we say the stack underflows, which is normally an error.If S.top exceeds n, the stack overflows.

 

STACK-EMPTY(S)

if S.top ==

    return TRUE

else return FALSE

PUSH(S, x)

S.top = S.top +

S[S.top] = x

POP(S)

if STACK-EMPTY(S)

    error 'underflow'

else S.top = S.top -

    return S[S.top + ]

//we can implement  a stack of at mostnelements withan arraySŒ1::n.

DIY-FULL(S)

if S.top < n

    return FLASE

else return TRUE

DIY-POP(S)

if STACK-EMPTY(S)

    error 'underflow'

else if DIY-FULL(S)

    error 'overflow'

else S.top = S.top -

     return S[S.top + ]