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CS 106X – Programming Abstractions in C++Cynthia Bailey Lee
CS2 in C++ Peer Instruction Materials by Cynthia Bailey Lee
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2
Today’s Topics
1. ADTs/Containers: what are they?2. Stack3. Compare Stack and Vector
implementations of the same code4. [Maybe Monday] Stack example: Reverse
Polish Notation evaluator
ADTs
ADTs Programming language independent
models of common containers They encompass not only the nature of
the data, but ways of accessing it
They form a rich vocabulary of nouns and verbs, often drawing on analogies to make their use intuitive, and to give code written in them a certain literary quality
"Hope" is the thing with feathersBY EMILY DICKENSON
“Hope” is the thing with feathers -That perches in the soul -And sings the tune without the words -And never stops - at all -
And sweetest - in the Gale - is heard -And sore must be the storm -That could abash the little BirdThat kept so many warm -
I’ve heard it in the chillest land -And on the strangest Sea -Yet - never - in Extremity,It asked a crumb - of me.
Some ADTs implemented in the Stanford Libraries Vector Grid Graph Map (and HashMap) Set (and HashSet) PriorityQueue Queue Stack
ADT: Grid
static void clearBoard(Grid<bool>& board);
int main(){ Grid<bool> board(8,8); clearBoard(board); //not strictly necessary // …more code to come… return 0;}
static void clearBoard(Grid<bool>& board){ for (int i=0; i<board.numRows(); i++){ for (int j=0; j<board.numCols(); j++){ board[i][j] = false; } }}
queensafety.cpp
Stacks
New ADT: Stacktemplate <typename ValueType> class Stack {
public: Stack(); virtual ~Stack(); int size() const; bool isEmpty() const; void clear(); void push(ValueType value); ValueType pop(); ValueType peek() const; std::string toString();
private:
};
stack.h
-Redacted-
New ADT: Stacktemplate <typename ValueType> class Stack {
public: Stack(); virtual ~Stack(); int size() const; bool isEmpty() const; void clear(); void push(ValueType value); ValueType pop(); ValueType peek() const; std::string toString();
private:
};
stack.h
-Redacted- This image was released by the National Cancer Institute, an agency part of the National Institutes of Health, with the ID 8368
Using a Stack to buffer file inputvoid mystery(ifstream& infile) { Stack<string> lines; string line; while (getline(infile,line)) { lines.push(line); } infile.close(); while (!lines.isEmpty()) { cout << lines.pop() << endl; }}
What does this code do?A. Prints all lines of a
file to cout B. Prints only the first
line of a file to coutC. Prints only the last
line of a file to coutD. Prints all lines of a
file to cout in reverse
E. All/ none/ more than one of the above
void mystery(ifstream& infile) { Stack<string> lines; string line; while (getline(infile,line)) { lines.push(line); } infile.close(); while (!lines.isEmpty()) { cout << lines.pop() << endl; }}
Using a Stack to buffer file inputWhat does this code do?A. Prints all lines of a
file to cout B. Prints only the first
line of a file to coutC. Prints only the last
line of a file to coutD. Prints all lines of a
file to cout in reverse
E. All/ none/ more than one of the above
Why do I need Stack? I could have done that with a Vector!
Stack or Vector?
Vector<string> lines;
lines.insert(lines.size(), line);
cout << lines[lines.size()-1] << endl;lines.remove(lines.size()-1);
void mystery(ifstream& infile) { Stack<string> lines; string line; while (getline(infile,line)) { lines.push(line); } infile.close(); while (!lines.isEmpty()) { cout << lines.pop() << endl; }}
Vector versionvoid mystery2(ifstream& infile) { Vector<string> lines; string line; while (getline(infile,line)) { lines.insert(lines.size(),line); } infile.close(); while (!lines.isEmpty()) { cout << lines[lines.size()-1] << endl; lines.remove(lines.size()-1); }}
Applications of StacksWe’ve seen one (buffering input and giving it back in reverse—LIFO—order). What else are Stacks good for?
Operator Precedence and Syntax Trees Ignoring operator precedence rules, how
many distinct results are there to the following arithmetic expression? 3 * 3 + 3 * 3
A. 1B. 2C. 3D. 4E. More than 4
Reverse Polish Notation Ambiguities don’t exist in RPN Also called “postfix” because the
operator goes after the operands
Postfix (RPN): 4 3 * 4 3 * +
Equivalent Infix: (4*3) + (4*3)
http://commons.wikimedia.org/wiki/File:Hewlett-Packard_48GX_Scientific_Graphing_Calculator.jpg
Reverse Polish Notation This postfix expression:
4 3 * 7 2 5 * + + Is equivalent to this infix expression:A. ((4*3) + (7*2)) + 5B. (4*3) + ((7+2) + 5)C. (4*3) + (7 + (2*5))D. Other/none/more than one
http://commons.wikimedia.org/wiki/File:Hewlett-Packard_48GX_Scientific_Graphing_Calculator.jpg
Stacks and RPN Evaluate this expression with the help of a
stack Encounter a number: PUSH it Encounter an operator: POP two numbers and
PUSH result 4 3 * 7 2 5 * + +
4 3
4
12
*7
12
2
7
12
* ?
?
?
?
?
?
Contents of the stack, reading from top down:
A. 7, 12B. 2, 7, 12C. 10, 7,12D. 10, 5, 2,
7, 12E. Other
5
2
7
12
Stacks and RPN:What does that look like in code?
Evaluate this expression with the help of a stack Encounter a number: PUSH it Encounter an operator: POP two numbers and PUSH result
43*725*++
