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
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
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
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
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
int main()
{
char *a="BASIC";
for(int i=4; i>=0; i--)
putchar(*(a+i));
putchar('\n');
return 0;
}
例5
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
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
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
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
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
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
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
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）
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）
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）
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;
}
