Character stack ADT program

how can I write a program, using ADT that process a text strings,

Code:

void push(char ch); // pushes the character ch onto the stack;

char pop(); // pops and returns the top character;

int isEmpty(); // returns 1 if the stack is empty, 0 otherwise;

int reverseSentence(char str[]); // main function;

ie, if

Code:

str

is "ABC D2EF. GHI3J. KLM", then after calling the function

Code:

str

becomes "FED CBA. JIHG. MLK". The function should also return 3, indicating that there are 3 sentences.

Can someone spent a little time to help on my question? thk a lot.

A stack ADT is dreadfully simple if you don't worry about error handling.

Code:

static char   stack[BUFSIZ];
static size_t top = 0;

static void
push(char ch)
{
  stack[top++] = ch;
}

static char
pop(void)
{
  return stack[--top];
}

static int
isEmpty(void)
{
  return top == 0;
}

As for the reverseSentence function, really all you have to do is walk down the sentence looking for punctuation. Before you find a sentence terminator, push each character on to the stack. Once you find the terminator, start popping and saving to the beginning of the sentence. You would probably need two indices. The first would be your index for pushing and searching, the second would be your index for saving the beginning of a sentence and rewriting the reversed sentence. Something like this:

Code:

pusher := string

while not end do
  saver := pusher
  while not end and string[pusher] != '.' do
    push(string[pusher])
    pusher := pusher + 1
  loop
  while not isEmpty() do
    string[saver] := pop()
    saver := saver + 1
  loop
  pusher := pusher + 1; # Remove '.'
  while not end and isspace(string[pusher]) do
    pusher := pusher + 1
loop