# C++程式設計期中考複習

###### tags: `C++程式練習`

>存成c.pp檔

## C++ 基本內容:

* 整數 int long : 32位元
* 整數 long long int : 64位元
* 浮點數 float , double

>cin,cout ,iostream,stdexcept,cmath,namespace,iomanip

* 類別與物件
* 類別:總體(概念性)
* 物件:個體(實體性)

## C++切檔案(三片)

### 類別定義(.h檔)

class Temp
{
friend void fun(Temp &,int); //

public:
Temp();
Temp(const Temp &);
private:
int data1;
float data2;

};

> 存成 temp.h 檔

:::success
friend 可以讓 函式 使用 物件 裡的 private參數.
:::

### 類別實作(.cpp檔)

> 讀入 temp.h 檔

#include "temp.h"
Temp::Temp():data1(0),data2(0.0){}
Temp::Temp(const Temp &t)
{
this -> data1 = t.data1;
this -> data2 = t.data2;
}

> 存成 temp.cpp 檔

### 主程式(main())

> 讀入 temp.cpp 檔

# include <iostream>
# include "Temp.cpp"

void fun(Temp &t, int n)
{
t.data1 = n;
}

int main()
{
Temp *t = new Temp();
fun(*t ,100);
}

> 存檔為main.cpp

## C++ 輸出格式

> setw(5):設定輸出格式有幾位(5)
> setfill(' '):將未滿設定位數的以(空格)補齊

#include <iomanip>
#include <iostream>
using manespace std;
        
int main()
{
  int number;
  cin >> number;
  cout << setfill( 'x' ) << setw( 5 ) << number<<endl;
}

> setprecision(4) : 設定輸出的位數(4)
> fixed : 寫在輸出資料前，限制小數位數(取小數點後4位)

#include <iostream>
#include <iomanip>
using namespace std;

int main(void)
{
    double X,Y;
    cin >> X >> Y;
    cout << setprecision(6) << fixed << X/Y << endl ; 
    return 0;
}

## control flow example

> countine : 跳過本次迴圈接下來執行的程式，進入下一次的迴圈
> break : 直接跳出程式中最近的迴圈

#include <iostream>
using namespace std;
class Grade{
    public:
        Grade():size(0),sum(0){}
        void setGrade(int x){
            grade[size++]=x;
        }
        void computeSum(){
            for(int i=0;i<size;i++){
                sum=sum+grade[i];
            }
        }
        float retAvg(){
            if(size!=0) return (float)sum/size;
            else return -1.0;
        }
        void printAvg(){
            float avg = retAvg();
            if((avg<0) cout<<"No valid grade is entered"<<endl;
            else cout<<"The averaged score is: "<<avg<<endl;
        }
    private:
        int grade[1000],size,sum;
};

int main(){
    Grade g1;
    int grade;
    for(;;){
        cout<<"Enter a grade: "<<endl;
        cin>>grade;
        if(grade==-1)break;
        if((grade<0) || (grade>100))continue;
        g1.setGrade(grade);
    }
    g1.computeSum();
    g1.printAvg();
    return 0;
}

## template< typename T > 模板使用

#include <iostream>
using namespace std;
template <typename R,typename M>
void bank(M money,R rate)
{
    cout << money * rate<<endl;;
}

int main()
{   
    int a=1000,b=2;
    float c=1.1,d=2345.1;
    bank(a,b);
    bank(a,c);
    bank(d,c);
    bank(d,b);
    return 0;
}

>寫一個函式做陣列的加總，不限資料型態。

template <typename T>
T sum(T *arr, int len) {
T ans ;
for(int i =0; i<len;i++)
{
ans += arr[i];
}
return ans;
}

> 設計一template function 將陣列由小到大排序

template <typename T>
void sort(T arr[], int len) 
{
  for(int i =0;i<len-1;i++)
  {
    for(int j=1;j<len;j++)
    {
        if(arr[j] < arr[j-1])
        {
          T temp = arr[j-1];
          arr[j-1] = arr[j];
          arr[j] = temp;
        }
    }
  }
}

## throw 出錯誤訊息

> stdexcept 語法 : throw,try,catch

#include <iostream>
#include <iomanip>
#include <stdexcept> // for invalid_argument exception class
using namespace std;
class test
{
public:
    void setGrade( int x )
    {
        // validate grade
        if ( x >= 0 && x <=100 ){
            grade=x;
        }
        else  
            throw invalid_argument("invalid grade");
        }
        void printGrade(){
            cout << setfill( '0' ) << setw( 3 ) << grade<<endl;
        }
private:
    int grade;
};


int main()
{
  test t,*tptr=&t,&reft=t;
  int g;
  
  cout<<"Enter a grade"<<endl;
  cin>>g;
  try
  {
      t.setGrade( g );
      t.printGrade();
  }
  catch ( invalid_argument &e )
  {
      cout << "\n\nException: " << e.what() << endl;   }

  cout<<"Enter a grade"<<endl;
  cin>>g;
  try
  {
      tptr->setGrade( g );
      tptr->printGrade();
  }
  catch ( invalid_argument &e )
  {
      cout << "\n\nException: " << e.what() << endl;
  }
  
  cout<<"Enter a grade"<<endl;
  cin>>g;
  try
  {
      reft.setGrade( g );
      reft.printGrade();
  }
  catch ( invalid_argument &e )
  {
      cout << "\n\nException: " << e.what() << endl;
  }
} 

## friend function　應用

#include <iostream>
#include <iomanip>
using namespace std;
class Time
{
  friend void setT(Time &,int,int,int); // friend declaration
  friend void getT(Time &);
private:
  int hour,minute,second; // data member
};

void setT( Time &c, int h, int m, int s )
{
  c.hour=h;
  c.minute=m;
  c.second=s;
}

void getT( Time &c)
{
  cout<<setfill('0')<<setw(2)<<c.hour<<":";
  cout<<setw(2)<<c.minute<<":";
  cout<<setw(2)<<c.second<<endl;
}

int main()
{
  Time t;
  setT(t,1,1,1); // set time using a friend function
  getT(t); //get time using a friend function
  return 0;
}

## recursive 遞迴實作