CS31 Discussion 1E Spring 17: week 05 TA: Bo-Jhang Ho - PowerPoint PPT Presentation

CS31 Discussion 1E Spring 17’: week 05 TA: Bo-Jhang Ho bojhang@cs.ucla.edu Credit to former TA Chelsea Ju

Road map of CS31 String Array Function Class Variable If / else Loops Pointer

Today’s Agenda } Use project 3 to get more insights about functions } Peer discussion

When we talk about function… } How function are executed in a program } Consumer-Provider relation

An example of a function int square(int a) { return a * a; } int main() { int a = 3; int b = 6; cout << square(a + b) << endl; return 0; } } Are two variable a’s the same?

An example of a function int square(int a) { return a * a; } int main() { int a = 3; int b = 6; cout << square(a + b) << endl; return 0; } } Different functions have their own variable sets } Try it on VC++ / Xcode

What is your role? User Provider } How to use the function? } What’s the goal of the function? } How do you expect users to use this function? } How do you implement it?

User Math example 10 1 + 2.7 cout <<

User Math example #include <iostream> using namespace std; int main() { cout << ???????????????????? << endl; return 0; }

User Math example } Step 1: Use your own words to ask Google

User Math example } Step 1: Use your own words to ask Google } Step 2: Read the parameter description carefully

User Math example #include <iostream> #include <cmath> using namespace std; int main() { cout << (1 + pow(2.7, 10.0)) << endl; return 0; }

User Dice throw example cout <<

User Dice throw example } Step 1: Use your own words to ask Google

User Dice throw example } Step 1: Use your own words to ask Google } Step 2: Read the parameter description carefully

User Math example #include <iostream> #include <cstdlib> using namespace std; int main() { cout << (rand() % 6 + 1) << endl; return 0; }

User Math example #include <iostream> #include <cstdlib> using namespace std; int main() { cout << (rand() % 6 + 1) << endl; return 0; } } Question: why it always give the same value?

User Project 3 warm-up } What’s the difference between #include “…” and #include <...>?

User Project 3 warm-up } *.h shows the “interface” of the functions } And this is what you need only } *.cpp should be included to make the program complete } You’re welcome to check the details, but it’s not necessary

Provider Questions you have to ask yourself when developing a function } What’s the goal of the function? } How do you expect users to use this function? } What information have to pass to your function? } What message are you going to pass back? } How do you implement it?

Provider 1. What’s the goal of the function

Provider 2. How people are going to use this function A: Hey, I will give you a base and an exponent B: Sure, I will give you the result

Provider 2. How people are going to use this function

Provider 2. How people are going to use this function Please pass a coordinate (r, c) to me, remember to mention whether it’s a horizontal line or a vertical line, also give me the length as well as the character. Let me know the mode: I can support both foreground and background. If I can successfully draw a line based on the parameters you gave me, I tell you true, otherwise I reply false.

Provider 2. How people are going to use this function distance true dir plotChar Start at (r, c) false

Provider 3. How to implement } Modular design!

Provider 3. How to implement } Modular design!

Provider 3. How to implement } Modular design!

Determine function call graph void printSpaceStarLine(int numSpaces, int numStars); void printLayer(int startNumSpaces, int startNumStars) { printSpaceStarLine(startNumSpaces, startNumStars); printSpaceStarLine(startNumSpaces - 1, startNumStars + 2); printSpaceStarLine(startNumSpaces - 2, startNumStars + 4); } int main() { printLayer(5, 1); // * // *** // ***** printLayer(4, 3); // *** // ***** // ******* printLayer(3, 5); // ***** // ******* // ********* printLayer(2, 7); // ******* // ********* //*********** printSpaceStarLine(4, 3); // *** printSpaceStarLine(4, 3); // *** return 0; }

Determine function call graph void printSpaceStarLine(int numSpaces, int numStars); void printLayer(int startNumSpaces, int startNumStars) { printSpaceStarLine(startNumSpaces, startNumStars); printSpaceStarLine(startNumSpaces - 1, startNumStars + 2); printSpaceStarLine(startNumSpaces - 2, startNumStars + 4); } int main() { printLayer(5, 1); printLayer(4, 3); printLayer(3, 5); printLayer(2, 7); printSpaceStarLine(4, 3); printSpaceStarLine(4, 3); return 0; } main() paintLayer() paintSpaceStarLine() Call direction

Determine function call graph int factorial(int n) { void printFactorial(int n) { int prod = 1; int prod = 1; for (int i = 2; i <= n; i++) for (int i = 2; i <= n; i++) prod *= i; prod *= i; return prod; for (int k = 1; k <= 6; k++) { } cout << "The factorial of " << k << " is " int main() { << factorial(k) << endl; for (int k = 1; k <= 6; k++) { } cout << "The factorial of " } << k << " is " << factorial(k) << endl; int main() { } for (int k = 1; k <= 6; k++) } printFactorial(k); } Function fun question 5 Function fun question 4 main() factorial() main() printFactorial() Call direction

Determine function call graph int factorial(int n) { int prod = 1; for (int i = 2; i <= n; i++) prod *= i; return prod; } void printFactorial(int n) { for (int k = 1; k <= n; k++) { cout << "The factorial of " << k << " is " << factorial(k) << endl; } } int main() { for (int k = 1; k <= 6; k++) printFactorial(k); } main() printFactorial() factorial()

Provider 3. How to implement Always pay attention to what are available to you!

Provider Project 3 warm-up draw() clearGrid() setChar() getChar()

Provider Project 3 warm-up main() draw() clearGrid() setChar() getChar()

Provider Project 3 – Phase 2 plotLine() What’s the call relation here? draw() clearGrid() setChar() getChar()

Provider Project 3 – Phase 2 plotLine() draw() clearGrid() setChar() getChar()

Provider Project 3 – Phase 3 main() executeCommands() plotLine() draw() clearGrid() setChar() getChar()

Provider Project 3 – Phase 3 main() executeCommands() C F@ B@ H00 V00 plotLine() draw() clearGrid() setChar() getChar()

Provider Project 3 – Phase 3 main() executeCommands() C F@ B@ H00 V00 plotLine() draw() clearGrid() setChar() getChar()

Provider Project 3 - executeCommands() } A parser question Give me the "35 + 27 * 69" calculation result T ell me the "report.docx" "report.png" file type Generate a "int main() { return 0; }" program

Provider Project 3 - executeCommands() } A parser question } A typical approach: } Tokenize } Interpret / convert tokens "v2b h12fHh1fih0"

Provider Project 3 - executeCommands() } A parser question } A typical approach: } Tokenize } Interpret / convert tokens "v2b h12fHh1fih0"

Provider Project 3 - executeCommands() } A parser question } A typical approach: } Tokenize } Interpret / convert tokens } Why parsing is hard? } The length of tokens vary } There can be many exceptions and hard to come out a unified parsing strategy } In most cases, there are constraints across tokens (but not in this assignment) } Have to report “precise” error position

Provider Project 3 - executeCommands() } Write down a lot of both good examples and bad examples

Provider Project 3 - executeCommands() } Tokenize: Look forward strategy } Separate into several cases: } C } F@ } B@ } H-- "v2b h12fHh1fih0" } H2 } H22 } H-2 } H-22 } V

Discussion time } Find a partner and tell him/her what you have done, what program you encounter now } Brain storming the solution } Read code, use debugger help you, give suggestions