SLIDE 1
CS31 Discussion 1E
Spring 17’: week 05
TA: Bo-Jhang Ho
bojhang@cs.ucla.edu
Credit to former TA Chelsea JuRoad map of CS31
Variable If / else Loops Pointer Array Function Class String
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 - - 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 Todays Agenda } Use project 3 to get more
SLIDE 2
SLIDE 3
Today’s Agenda
} Use project 3 to get more insights about functions } Peer discussion
SLIDE 4
When we talk about function…
} How function are executed in a program } Consumer-Provider relation
SLIDE 5
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?
SLIDE 6
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
SLIDE 7
What is your role?
} How to use the function?
User Provider
} What’s the goal of the
function?
} How do you expect users
to use this function?
} How do you implement
it?
SLIDE 8
Math example
User
1 + 2.7
cout <<
10
SLIDE 9
Math example
User
#include <iostream> using namespace std; int main() { cout << ???????????????????? << endl; return 0; }
SLIDE 10
Math example
User
} Step 1: Use your own words to ask Google
SLIDE 11
Math example
User
} Step 1: Use your own words to ask Google } Step 2: Read the parameter description carefully
SLIDE 12
Math example
User
#include <iostream> #include <cmath> using namespace std; int main() { cout << (1 + pow(2.7, 10.0)) << endl; return 0; }
SLIDE 13
Dice throw example
User
cout <<
SLIDE 14
Dice throw example
User
} Step 1: Use your own words to ask Google
SLIDE 15
Dice throw example
User
} Step 1: Use your own words to ask Google } Step 2: Read the parameter description carefully
SLIDE 16
Math example
User
#include <iostream> #include <cstdlib> using namespace std; int main() { cout << (rand() % 6 + 1) << endl; return 0; }
SLIDE 17
Math example
User
#include <iostream> #include <cstdlib> using namespace std; int main() { cout << (rand() % 6 + 1) << endl; return 0; }
} Question: why it always give the
same value?
SLIDE 18
Project 3 warm-up
User
} What’s the difference between
#include “…” and #include <...>?
SLIDE 19
Project 3 warm-up
User
} *.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
SLIDE 20
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
SLIDE 21
- 1. What’s the goal of the function
Provider
SLIDE 22
- 2. How people are going to use this function
Provider
A: Hey, I will give you a base and an exponent B: Sure, I will give you the result
SLIDE 23
- 2. How people are going to use this function
Provider
SLIDE 24
- 2. How people are going to use this function
Provider
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.
SLIDE 25
- 2. How people are going to use this function
Provider
Start at (r, c) dir distance plotChar true false
SLIDE 26
- 3. How to implement
} Modular design!
Provider
SLIDE 27
- 3. How to implement
} Modular design!
Provider
SLIDE 28
- 3. How to implement
} Modular design!
Provider
SLIDE 29
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; }
SLIDE 30
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
SLIDE 31
Determine function call graph
int factorial(int n) { int prod = 1; for (int i = 2; i <= n; i++) prod *= i; return prod; } int main() { for (int k = 1; k <= 6; k++) { cout << "The factorial of " << k << " is " << factorial(k) << endl; } } void printFactorial(int n) { int prod = 1; for (int i = 2; i <= n; i++) prod *= i; 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 4 Function fun question 5
main()
Call direction
factorial() main() printFactorial()
SLIDE 32
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); }
factorial() main() printFactorial()
SLIDE 33
- 3. How to implement
Provider
Always pay attention to what are available to you!
SLIDE 34
Project 3 warm-up
Provider
setChar() clearGrid() getChar() draw()
SLIDE 35
Project 3 warm-up
Provider
setChar() clearGrid() getChar() draw() main()
SLIDE 36
Project 3 – Phase 2
Provider
setChar() clearGrid() getChar() draw() plotLine()
What’s the call relation here?
SLIDE 37
Project 3 – Phase 2
Provider
setChar() clearGrid() getChar() draw() plotLine()
SLIDE 38
Project 3 – Phase 3
Provider
setChar() clearGrid() getChar() draw() plotLine() executeCommands() main()
SLIDE 39
Project 3 – Phase 3
Provider
setChar() clearGrid() getChar() draw() plotLine() executeCommands() main()
C F@ B@ H00 V00
SLIDE 40
Project 3 – Phase 3
Provider
setChar() clearGrid() getChar() draw() plotLine() executeCommands() main()
C F@ B@ H00 V00
SLIDE 41
Project 3 - executeCommands()
Provider
} A parser question
"35 + 27 * 69" "report.docx" "report.png" "int main() { return 0; }" Give me the calculation result T ell me the file type Generate a program
SLIDE 42
Project 3 - executeCommands()
Provider
} A parser question } A typical approach:
} Tokenize } Interpret / convert tokens
"v2b h12fHh1fih0"
SLIDE 43
Project 3 - executeCommands()
Provider
} A parser question } A typical approach:
} Tokenize } Interpret / convert tokens
"v2b h12fHh1fih0"
SLIDE 44
Project 3 - executeCommands()
Provider
} 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
SLIDE 45
Project 3 - executeCommands()
Provider
} Write down a lot of both good examples and bad
examples
SLIDE 46
Project 3 - executeCommands()
Provider
} Tokenize: Look forward strategy } Separate into several cases:
} C } F@ } B@ } H--
} H2 } H22 } H-2 } H-22
} V
"v2b h12fHh1fih0"
SLIDE 47
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