第七讲：输入输出与模版

作业习题解答

习题地址：http://cxsjsx.openjudge.cn/hw202007/

A:简单的SumArray

#include <iostream>
#include <string>
using namespace std;
template <class T>
T SumArray(T* a,T* b){
    T c= *a;
    for(T* i=a+1;i<b;i++)
    c+= *i;
    return c;
}
int main() {
    string array[4] = { "Tom","Jack","Mary","John"};
	cout << SumArray(array,array+4) << endl;
	int a[4] = { 1, 2, 3, 4};  //提示：1+2+3+4 = 10
	cout << SumArray(a,a+4) << endl;
	return 0;
}

B:简单的foreach

#include <iostream>
#include <string>
using namespace std;
template<class T1,class T2>
void MyForeach(T1* m, T1* n,T2 h ) {
    for (int i = 0; i < n-m; i++)
         h(*(s + i));
}
void Print(string s)
{
    cout << s;
}
void Inc(int & n)
{
    ++ n;
}
string array[100];
int a[100];
int main() {
    int m,n;
    while(cin >> m >> n) {
        for(int i = 0;i < m; ++i)
            cin >> array[i];
        for(int j = 0; j < n; ++j)
            cin >> a[j];
        MyForeach(array,array+m,Print);         
        cout << endl;
        MyForeach(a,a+n,Inc);         
        for(int i = 0;i < n; ++i)
            cout << a[i] << ",";
        cout << endl;
    }
    return 0;
}

C:简单的Filter

#include <iostream>
#include <string>
using namespace std;
template<class T1,class T2>
T1* Filter(T1*a,T1*b,T1*c,T2 f)
{
    for(T1*p=a;p<b;p++)
    {
        if(f(*p))
        {
            *c=*p;
            c++;
        }
    }
    return c;
}
bool LargerThan2(int n)
{
	return n > 2;
}
bool LongerThan3(string s) 
{
	return s.length() > 3;
}

string as1[5] = {"Tom","Mike","Jack","Ted","Lucy"};
string as2[5];
int  a1[5] = { 1,2,3,4,5};
int a2[5];
int main() {
	string * p = Filter(as1,as1+5,as2,LongerThan3);
	for(int i = 0;i < p - as2; ++i)
		cout << as2[i];
	cout << endl; 
	int * p2 = Filter(a1,a1+5,a2,LargerThan2);
	for(int i = 0;i < p2-a2; ++i)
		cout << a2[i] << ",";
	return 0;
}

D:你真的搞清楚为啥 while(cin >> n) 能成立了吗？

注：operator bool () 提供一个本类型到bool的隐式转换，不允许使用参数。

#include <iostream>
using namespace std;
class MyCin
{
bool flag;
public:
    MyCin():flag(true){}
    MyCin &operator>>(int &n){
        if(!flag) return*this;//不再把第二个数读入
        cin>>n;
        if(n==-1) flag=false;
        return *this;
    }
    operator bool(){return flag;}
};
int main()
{
    MyCin m;
    int n1,n2;
    while( m >> n1 >> n2) 
        cout  << n1 << " " << n2 << endl;
    return 0;
}

E:山寨版istream_iterator

为什么ccin一定要引用？

#include <iostream>
#include <string>

using namespace std;
template <class T>
class CMyistream_iterator
{
private:
    T value;
public:
    istream &ccin;
    CMyistream_iterator(istream &_ccin):ccin(_ccin){
        ccin>>value; //读入第一个数
    }
    T operator *(){
        return this->value;
    }
    void operator++ (int){ //后置++多一个参数
        ccin>>value;
    }
};
int main()  
{ 
	int t;
	cin >> t;
	while( t -- ) {
		 CMyistream_iterator<int> inputInt(cin);
		 int n1,n2,n3;
		 n1 = * inputInt; //读入 n1
		 int tmp = * inputInt;
		 cout << tmp << endl;
		 inputInt ++;   
		 n2 = * inputInt; //读入 n2
		 inputInt ++;
		 n3 = * inputInt; //读入 n3
		 cout << n1 << " " << n2<< " " << n3 << " ";
		 CMyistream_iterator<string> inputStr(cin);
		 string s1,s2;
		 s1 = * inputStr;
		 inputStr ++;
		 s2 = * inputStr;
		 cout << s1 << " " << s2 << endl;
	}
	 return 0;  
}

F:这个模板并不难

#include <iostream>
#include <string>
#include <cstring>
using namespace std;
template <class T>  
class myclass {
private:
    T* p;int size;
public:
    myclass(T* a,int b)
	{
		p=new T[b+1];
		size=b;
		for(int i=0;i<size;i++)
		p[i]=a[i];
		p[size]=0;
	}
    ~myclass( ) {
		delete [] p;
	}
	void Show()
	{
		for( int i = 0;i < size;i ++ ) {
			cout << p[i] << ",";
		}
		cout << endl;
	}
};
int a[100];
int main() {
	char line[100];
	while( cin >> line ) {
		myclass<char> obj(line,strlen(line));;
		obj.Show();
		int n;
		cin >> n;
		for(int i = 0;i < n; ++i)
			cin >> a[i];
		myclass<int> obj2(a,n);
		obj2.Show();
	}
	return 0;
}

G:排序，又见排序!

#include <iostream>
using namespace std;

bool Greater2(int n1,int n2) 
{
	return n1 > n2;
}
bool Greater1(int n1,int n2) 
{
	return n1 < n2;
}
bool Greater3(double d1,double d2)
{
	return d1 < d2;
}

template <class T1,class T2>
void mysort(T1*start,T1*end,T2 p){
	for(int i=1;i<=end-start-1;i++)
	{
		for(int j=0;j<end-start-i;j++)
		{
			if(!p(start[j],start[j+1]))
			{
				T1 temp=start[j];
				start[j]=start[j+1];
				start[j+1]=temp;
			}
		}
	}
}

#define NUM 5
int main()
{
    int an[NUM] = { 8,123,11,10,4 };
    mysort(an,an+NUM,Greater1); //从小到大排序 
    for( int i = 0;i < NUM; i ++ )
       cout << an[i] << ",";
    mysort(an,an+NUM,Greater2); //从大到小排序 
    cout << endl;
    for( int i = 0;i < NUM; i ++ )
        cout << an[i] << ","; 
    cout << endl;
    double d[6] = { 1.4,1.8,3.2,1.2,3.1,2.1};
    mysort(d+1,d+5,Greater3); //将数组从下标1到下标4从小到大排序 
    for( int i = 0;i < 6; i ++ )
         cout << d[i] << ","; 
	return 0;
}