What is a stack (at the logical level)?

Give an example of a stack in everyday life.

1. In problems 1 and 2, find the output of each program fragment. Show your work.

   apstack S;
int x = 2, y = 3;
S.push(x);
S.push(2*y);
S.push(4);
S.pop(y);
S.push(7);
S.pop( );
x = S.top( );
int n = S.length( );
for(int i=0; i<n;i++)
   S.push(n);
while( ! S.isEmpty( ) )
{
   S.pop(y);
   System.out.println(y);
}
System.out.println("x is " +  x);

2. apstack R, S, T;
for(int i=10; i<50; i+=10)
   S.push( i );
T = S;
int a, b;
while ( ! S.isEmpty( ) )
{
   S.pop(a);
   R.push(a);
}
int n = T.length( );
for(int i=0; i<n; i++)
{
   R.pop(a);
   T.pop(b);
   System.out.println(a + " " + b);
}
System.out.println(" R T");

3. Write each of the following functions that print the contents of a stack across a page leaving the stack unchanged.

   void displayTopFirst(apstack S)
//pre- the stack has been initialized
//post- stack's elements are displayed across the page
// without spaces, top first, followed by an end-of-
// line, the stack is unchanged
{
   ...
}

4. void displayTopLast(apstack S)
//pre- the stack has been initialized
//post- stack's elements are displayed across the page
// without spaces, top last, followed by an end-of-line;
// the stack is unchanged
{
   ...
}

5. Write a Boolean function which returns true if an String parameter contains matching and non-overlapping brackets - ( ) [ ] { }; otherwise, the function returns false. For example,
   • "[N(ov)(emb)er]1st" returns true
   • "{Oc[t}ober2]3rd" returns false

   Hint: Push opening symbols onto a stack of characters. When a closing symbol is found, pop the stack to see if the brackets match.

   Boolean bracketsMatch(String str)
{
   ...
}