1. Speaker: Liu Yu-Jiun Date: 2009/04/08
Recitation Course 0408
Speaker: Liu Yu-Jiun
Date: 2009/04/08

2. Outline
Ch 6 重點整理
HW2 pseudo code
HW2 評分新制

3. Functions Called methods or procedures in other languages
Allow programmers to modularize a program by separating its tasks into self-contained units
Statements in function bodies are written only once
Reused from perhaps several locations in a program
Hidden from other functions
Avoid repeating code
Enable the divide-and-conquer approach
Reusable in other programs
User-defined or programmer-defined functions

4. Function (Cont.) A function is invoked by a function call
Called function either returns a result or simply returns to the caller
Function calls form hierarchical relationships

5. <cmath>
Global functions，不屬於任何的類別，只要把標頭檔include進來就可以在程式任何地方使用這些函式

6. Return control Three ways to return control to the calling statement:
If the function does not return a result:
Program flow reaches the function-ending right brace (}) or
Program executes the statement return;
If the function does return a result:
Program executes the statement return expression;
expression is evaluated and its value is returned to the caller

7. Function Prototypes and Argument Coercion7
Function Prototypes and Argument Coercion
Function prototype
Also called a function declaration
Indicates to the compiler:
Name of the function
Type of data returned by the function
Parameters the function expects to receive
Number of parameters
Types of those parameters
Order of those parameters 7

8. Outline (1 of 4) #include and using for function time8
Outline
fig06_11.cpp
(1 of 4)
#include and using for function time
Enumeration to keep track of the game status
Declaring a variable of the user-defined enumeration type
Seeding the random number generator with the current time 8

9. Outline (2 of 4) Assigning an enumeration constant to gameStatus9
Outline
fig06_11.cpp
(2 of 4)
Assigning an enumeration constant to gameStatus
Comparing a variable of an enumeration type to an enumeration constant 9

10. Function that performs the task of rolling the dice10
Outline
fig06_11.cpp
(3 of 4)
Function that performs the task of rolling the dice 10

11. 11
Outline
fig06_11.cpp
(4 of 4) 11

12. HW2 pseudo code

13. #include <iostream> using namespace std; class RationalNumber{
// rational.h
#include <iostream>
using namespace std;
class RationalNumber{
friend ostream& operator<< (ostream &, const RationaNumber&);
friend istream& operator>> (istream &, RationalNumber&);
public:
RationalNumber();
RationalNumber(int = 0, int = 1);
RationalNumber operator+(const RationalNumber&);
RationalNumber operator-(const RationalNumber&);
RationalNumber operator*(const RationalNumber&);
RationalNumber operator%(const RationalNumber&);
private:
int numerator;
int denominator;
bool sign;
void reduction(void);
int gcd(int, int); };
可以存取類別中的成員與成員函式
1.是哪個類別的朋友，就宣告在哪個類別中
2.不是成員函式，所以寫函式內容時，不用加”類別名稱::”
3.呼叫friend函式時，不用”object.”
const : constant
修飾後面的東西，確保後面的東西不會被更改。

14. 課本習題6.45 // rational.cpp // 運算部分
RationalNumber RationalNumber::operator+(const RationalNumber& in){
n1 = (sign)?(this->numerator):(0 - this->numerator);
n2 = (in.sign)?(in.numerator):(0 - in.numerator);
tmp_d = this->denominator * in.denominator;
tmp_n = n1 * in.denominator + n2 * this->denominator;
RationalNumber rev(tmp_n, tmp_d);
rev.reduction(); //把結果約個分
return rev; }
RationalNumber RationalNumber::operator-(const RationalNumber& in){
....
RationalNumber RationalNumber::operator*(const RationalNumber& in){
RationalNumber RationalNumber::operator%(const RationalNumber& in){
// 約分部份，把最後算出來的結果約個分
void reduction(){
.....
int gcd(int x, int y){
return ((y != 0) ? gcd(y, x%y) : x);
?: (c++內唯一的三元運算子)
(condition) ? (value if true) : (value if false)
誰呼叫它，誰就是”this”。
“this”是一個指標，指向物件。
課本習題6.45

15. 這兩個運算子多載函式是friend，所以前面不用加上”Rational::”
// rational.cpp
// 輸入、輸出部分
istream& operator>>(istream& in, RationalNumber& val){
int n, d;
char ch;
if (!(in >> n))
return in;
ch = in.get();
if (ch != '/'){
do something.... }
else{
in >> d;
val.numerator = abs(n);
val.denominator = abs(d);
ostream& operator<<(ostream& out, const RationaNumber& val){
if (sign == 0){
out << "-";
if (val.denominator == 1){
out << val.numerator;
else {
out << val.numerator << "/" << val.denominator;
return out;
這兩個運算子多載函式是friend，所以前面不用加上”Rational::”
>>的部份比較需要處理，應該還需要記錄sign值

16. #include <iostream>
#include "rational.h"
using namespace std;
int main(){
RationalNumber r1, r2, ans;
char opr;
while(cin >> r1){
cin >> opr;
cin >> r2;
// 可以在這邊就檢查是否有除以零的情況...
if (opr == '+'){
ans = r1 + r2; }
else if (opr == '-'){
ans = r1 - r2;
cout << ans;
一堆的if...else if...else if...else...，可以換成switch。
switch(opr){
case ‘+’:
ans = r1 + r2;
break;
case ‘-’:
ans = r1 – r2;
default:
// 這裡就是非四則運算符號的情況處理 }

17. HW2 評分新制 Upload to system Demo Final score = max (upload, demo)
Deadline: 4/15 11:59 p.m.
Demo
Time: 4/15 7:30~10:00 p.m.
Explain your code to get 2 points.
Answer 1 question to get 1 point, total 3 questions.
Pass 1 example to get 1 point, total 3 examples.
The highest score of demo is 8 points.
Final score = max (upload, demo)