Embed Size (px)
Citation preview
1
Data Structures
CSCI 132, Spring 2014Lecture 6
Applications using Stacks
2
Recall the Stack classtypedef int Stack_entry;
const int maxstack =10 ; //small value for testing
class Stack {
public:
Stack();
bool empty()const;
Error_code pop();
Error_code top(Stack_entry &item)const;
Error_code push(const Stack_entry &item);
private:
int count ;
Stack_entry entry [maxstack ];
};
3
Implementing push( )
Error_code Stack ::push(const Stack_entry &item)
{
//Implement push() here
}
4
Implementing push( )
Error_code Stack ::push(const Stack_entry &item)
{
Error_code outcome =success ;
if (count >=maxstack) {
outcome =overflow ;
} else {
entry [count ]=item ;
count++;
}
return outcome ;
}
5
Implementing pop( )
Error_code Stack ::pop()
{
}
6
Implementing pop( )
Error_code Stack ::pop()
{
Error_code outcome =success ;
if (count ==0) {
outcome =underflow ;
} else {
count-- ;
}
return outcome ;
}
7
Implementing top( )
Error_code Stack ::top(Stack_entry &item) const
{
//implement top( )
}
8
Implementing top( )
Error_code Stack ::top(Stack_entry &item) const
{
Error_code outcome =success ;
if (count ==0){
outcome =underflow ;
} else {
item =entry [count - 1];
}
return outcome ;
}
9
Implementing empty( )
bool Stack ::empty( )const
{
//implement empty( )
}
10
Implementing empty( )
bool Stack ::empty( )const
{
bool outcome =true;
if (count >0) {
outcome =false;
}
return outcome ;
}
11
Implementing Stack( )
Stack ::Stack()
{ //implement Stack( )
}
12
Implementing Stack( )
Stack ::Stack()
{
count =0 ;
}
13
Reverse Polish Calculator:A stack application
• Numbers are pushed onto a stack as they are entered.
• An arithmetic operation is done on the top two items in the stack, which are popped off the stack. The result is pushed onto the stack.
• Reverse polish arithmetic allows you to do any arithmetic calculation without using parentheses.
• For example, the computation (6 + 2) is written as 6 2 + in reverse polish notation.
14
Example
Regular notation: (6 + 2) / (7 - 3)
Reverse Polish: 6 2 + 7 3 - /
6 66 2 2
287
888+ 7 7 43
3
- /
15
Rules for Calculator use
User enters a command:
?, =, +, -, *, or /
? means the next entry is a number.
= means print the result (top of stack).
All others mean perform the given arithmetic operation.
The main calculator program #include <stack> //stack class from the Standard Template Library
int main (void) {
char command ;
Stack stored_numbers;
cout <<"Enter a command: ";
cin >> command;
command = tolower(command);
while (command != 'q'){
if (command == '?'||command == '='||command == '+' ||
command == '-'||command == '*'||command == '/' ) {
do_command(command, stored_numbers);
} else {
cout <<"Please enter a valid command:"<<endl
<<"[?]push to stack [=]print top "<<endl
<<"[+][-][*][/]are arithmetic operations "<<endl
<<"[Q ]uit."<<endl;
}
cout << "Enter a command: ";
cin >> command;
command = tolower(command);
}
}
17
Processing commands
void do_command(char command ,Stack &numbers)
{
double p ,q ;
switch (command){
case '?':
break;
case '=':
break;
cout <<"Enter a real number:" ;
cin >>p ;
if (numbers.push(p)==overflow) {
cout <<"Warning:Stack full,lost number "<<endl;
}
if (numbers.top(p) == underflow) {
cout << "Stack empty." << endl;
} else {
cout << p <<endl;
}
18
More number processingcase '+':
break;
//Add options for further user commands.
} //end switch
} //end do_command
if (numbers.top(p)==underflow){
cout <<"Stack empty "<<endl ;
} else {
numbers.pop();
if (numbers.top(q)==underflow){
cout <<"Stack has just one entry "<<endl ;
numbers.push(p);
} else {
numbers.pop();
if (numbers.push(q + p)==overflow) {
cout <<"Warning:Stack full,lost result "<<endl ;
}
}
}
