1、阅读并运行下面的示例程序，掌握标准输入输出流的控制

例1

#include <iostream>
#include <math.h>
using namespace std;
int main()
{
    float a,b,c,disc;
    cout<<"please input a,b,c:";
    cin>>a>>b>>c;
    if (a==0)
        cerr<<"a is equal to zero,error!"<<endl;
    else if ((disc=b*b-4*a*c)<0)
        cerr<<"disc=b*b-4*a*c<0"<<endl;
    else
    {
        cout<<"x1="<<(-b+sqrt(disc))/(2*a)<<endl;
        cout<<"x2="<<(-b-sqrt(disc))/(2*a)<<endl;
    }
    return 0;
}

例2

#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
    int a;
    cout<<"input a:";
    cin>>a;
    cout<<"dec:"<<dec<<a<<endl;
    cout<<"hex:"<<hex<<a<<endl;
    cout<<"oct:"<<setbase(8)<<a<<endl;
    char *pt="China";
    cout<<setw(10)<<pt<<endl;
    cout<<setfill('*')<<setw(10)<<pt<<endl;
    double pi=22.0/7.0;
    cout<<setiosflags(ios::scientific)<<setprecision(8);
    cout<<"pi="<<pi<<endl;
    cout<<"pi="<<setprecision(4)<<pi<<endl;
    cout<<"pi="<<setiosflags(ios::fixed)<<pi<<endl;
    return 0;
}

例3

#include <iostream>
using namespace std;
int main()
{
    int a=21;
    cout.setf(ios::showbase);
    cout<<"dec:"<<a<<endl;
    cout.unsetf(ios::dec);
    cout.setf(ios::hex);
    cout<<"hex:"<<a<<endl;
    cout.unsetf(ios::hex);
    cout.setf(ios::oct);
    cout<<"oct:"<<a<<endl;
    char *pt="China";
    cout.width(10);
    cout<<pt<<endl;
    cout.width(10);
    cout.fill('*');
    cout<<pt<<endl;
    double pi=22.0/7.0;
    cout.setf(ios::scientific);
    cout<<"pi=";
    cout.width(14);
    cout<<pi<<endl;
    cout.unsetf(ios::scientific);
    cout.setf(ios::fixed);
    cout.width(12);
    cout.setf(ios::showpos);
    cout.setf(ios::internal);
    cout.precision(6);
    cout<<pi<<endl;
    return 0;
}

例4-1

#include <iostream>
using namespace std;
int main( )
{
    char *a="BASIC";		//字符指针指向'B'
    for(int i=4; i>=0; i--)
        cout.put(*(a+i));   //从最后一个字符开始输出
    cout.put('\n');
    return 0;
}

例4-2

#include<iostream>
#include<cstdio>
int main()
{
    char *a="BASIC";
    for(int i=4; i>=0; i--)
        putchar(*(a+i));
    putchar('\n');
    return 0;
}

例5

#include <iostream>
using namespace std;
int main( )
{
    float grade;
    cout<<"enter grade:";
    while(cin>>grade)  //能从cin流读取数据
    {
        if(grade>=85)
            cout<<grade<<" GOOD!"<<endl;
        if(grade<60)
            cout<<grade<<" fail!"<<endl;
        cout<<"enter grade:";
    }
    cout<<"The end."<<endl;
    return 0;
}

例6
（1）不带参数的get函数

#include<iostream>
#include<cstdio>
using namespace std;
int main( )
{
    int c;
    cout<<"enter a sentence:"<<endl;
    while((c=cin.get())!=EOF)
        cout.put(c);
    return 0;
}

(2) 有一个参数的get函数

#include<iostream>
#include<cstdio>
using namespace std;
int main( )
{
    char c;
    cout<<"enter a sentence:"<<endl;
    while(cin.get(c))  //读取一个字符赋给字符变量c，如果读取成功，cin.get(c)为真
        cout.put(c);
    cout<<"end"<<endl;
    return 0;
}

(3) 有3个参数的get函数

#include<iostream>
using namespace std;
int main( )
{
    char ch[20];
    cout<<"enter a sentence:"<<endl;
    cin.get(ch,10,'\n');//指定换行符为终止字符
    cout<<ch<<endl;
    return 0;
}

例7

#include <iostream>
using namespace std;
int main( )
{
    char ch[20];
    cout<<"enter a sentence:"<<endl;
    cin>>ch;
    cout<<"The string read with cin is:"<<ch<<endl;
    cin.getline(ch,20,'/');//读19个字符或遇'/'结束
    cout<<"The second part is:"<<ch<<endl;
    cin.getline(ch,20);    //读19个字符或遇'/n'结束
    cout<<"The third part is:"<<ch<<endl;
    return 0;
}

2、阅读并运行下面的示例程序，体会对文本文件的访问。
例11

#include<iostream>
#include <fstream>
#include<cstdlib>
using namespace std;
int main( )
{
    int a[10];
    ofstream outfile("f1.dat",ios::out);//定义文件流对象，打开磁盘文件"f1.dat"
    if(!outfile)                        //如果打开失败，outfile返回0值
    {
        cerr<<"open error!"<<endl;
        exit(1);
    }
    cout<<"enter 10 integer numbers:"<<endl;
    for(int i=0; i<10; i++) //向磁盘文件"f1.dat"输出数据
    {
        cin>>a[i];
        outfile<<a[i]<<" ";
    }
    cout<<"The numbers have been writen to file. "<<endl;
    outfile.close();       //关闭磁盘文件"f1.dat"
    return 0;
}

例12

#include<iostream>
#include <fstream>
#include<cstdlib>
using namespace std;
int main( )
{
    int a[10],max,i,order;
    ifstream infile("f1.dat",ios::in);
    //定义输入文件流对象，以输入方式打开磁盘文件f1.dat
    if(!infile)
    {
        cerr<<"open error!"<<endl;
        exit(1);
    }
    for(i=0; i<10; i++)
    {
        infile>>a[i];  //从磁盘文件读入10个整数，顺序存放在a数组中
        cout<<a[i]<<" ";
    }          //在显示器上顺序显示10个数
    cout<<endl;
    max=a[0];
    order=0;
    for(i=1; i<10; i++)
        if(a[i]>max)
        {
            max=a[i];                //将当前最大值放在max中
            order=i;                 //将当前最大值的元素序号放在order中
        }
    cout<<"max="<<max<<endl<<"order="<<order<<endl;
    infile.close();
    return 0;
}

例13

#include<iostream>
#include<fstream>
#include<cstdlib>
using namespace std;
void save_to_file( );
void get_from_file();
int main( )
{
    save_to_file( );
    //调用save_to_file( )，从键盘读入一行字符并将其中的字母存入磁盘文件f2.dat
    get_from_file( );
    //调用get_from_file()，从f2.dat读入字母字符，改为大写字母，再存入f3.dat
    return 0;
}

// save_to_file函数从键盘读入一行字符，并将其中的字母存入磁盘文件
void save_to_file( )
{
    ofstream outfile("f2.dat");
    //定义输出文件流对象outfile，以输出方式打开磁盘文件f2.dat
    if(!outfile)
    {
        cerr<<"open f2.dat error!"<<endl;
        exit(1);
    }
    char c[80];
    cin.getline(c,80);		   //从键盘读入一行字符
    for(int i=0; c[i]!=0; i++) //对字符逐个处理，直到遇′/0′为止
        if((c[i]>=65 && c[i]<=90)||(c[i]>=97 && c[i]<=122))//如果是字母字符
        {
            outfile.put(c[i]);       //将字母字符存入磁盘文件f2.dat
            cout<<c[i];
        }                            //同时送显示器显示
    cout<<endl;
    outfile.close();                 //关闭f2.dat
}

//从磁盘文件f2.dat读入字母字符，将其中的小写字母改为大写字母，再存入f3.dat
void get_from_file()
{
    char ch;
    ifstream infile("f2.dat",ios::in);
    //定义输入文件流outfile，以输入方式打开磁盘文件f2.dat
    if(!infile)
    {
        cerr<<"open f2.dat error!"<<endl;
        exit(1);
    }
    ofstream outfile("f3.dat");
    //定义输出文件流outfile，以输出方式打开磁盘文件f3.dat
    if(!outfile)
    {
        cerr<<"open f3.dat error!"<<endl;
        exit(1);
    }
    while(infile.get(ch))//当读取字符成功时执行下面的复合语句
    {
        if(ch>=97 && ch<=122)          //判断ch是否为小写字母
            ch=ch-32;                  //将小写字母变为大写字母
        outfile.put(ch);               //将该大写字母存入磁盘文件f3.dat
        cout<<ch;                      //同时在显示器输出
    }
    cout<<endl;
    infile.close( );                 //关闭磁盘文件f2.dat
    outfile.close();                 //关闭磁盘文件f3.dat
}

3、请写出下面程序的输出结果

（1）

#include <iostream> 
#include <fstream> 
using namespace std;
int main()
 {     
    fstream outfile,infile;     
    outfile.open("data.dat",ios::out);     
    outfile<<"1111111111"<<endl;     
    outfile<<"aaaaaaaaaa"<<endl;     
    outfile<<"AAAAAAAAAA"<<endl;
    outfile<<"**********"<<endl;
    outfile.close();     
    infile.open("data.dat",ios::in);     
    char line[80];     
    int i=0;     
    while(!infile.eof())     
    {         
        i++;         
        infile.getline(line,sizeof(line));         
        cout<<i<<": "<<line<<endl;     
    }     
    infile.close(); 
    return 0;
}

（2）说出程序的功能，并上机验证（请自建a.txt）

#include <iostream>
#include <fstream>
using namespace std;
int main()
{
    ifstream readFile;
    ofstream writeFile;
    char ch;
    readFile.open("a.txt", ios::in);
    writeFile.open("b.txt", ios::out);
    while (readFile.get(ch))
        writeFile.put(ch);
    readFile.close();
    writeFile.close();
    cout << "Finish!" << endl;
    return 0;
}

（3）

#include <iostream>
#include <fstream>
#include<cstring>
using namespace std;
int main()
{
    ifstream readFile;
    ofstream writeFile;
    char ch[100];
    readFile.open("a.txt", ios::in);
    writeFile.open("b.txt", ios::out);
    while (!readFile.eof())
    {
        readFile.getline(ch,100,'\n');
        writeFile.write(ch,strlen(ch));
        writeFile.write("\n",1);
    }
    readFile.close();
    writeFile.close();
    cout << "Finish!" << endl;
    return 0;
}