1 #include<iostream>
 2 #include<fstream>
 3 using namespace std;
 4 
 5 int main()
 6 {
 7     char automobile[50];
 8     int year;
 9     double a_price;
10     double d_price;
11 
12     //声明ofstream对象并将其同文件关联起来，若在程序运行前，不存在此文件，则open()将新建一个名为carinfo.txt的文件
13     ofstream outFile;
14     outFile.open("carinfo.txt");
15 
16     cout << "Enter the make and model of automobile: ";
17     cin.getline(automobile, 50);    //cin.getline:不断读取，直到遇到换行符（少于50个字符），在末尾加上一个空字符，换行符被丢弃
18     cout << "Enter the model year: ";
19     cin >> year;
20     cout << "Enter the original asking price；";
21     cin >> a_price;
22     d_price = 0.913*a_price;
23 
24     cout << fixed;    //表示用一般的方式输出浮点数，不用科学计数法,比如num=0.00001，cout输出为1e-005，加了fixed后再输出就为0.000010
25     cout.precision(2);   //第一位精确，第二位四舍五入，比如num = 318.15，precision(2)为3.2e+02,precision(4)为318.2
26     cout.setf(ios_base::showpoint);  //强制显示小数点
27     cout << "Make and model: " << automobile << endl;
28     cout << "Year: " << year << endl;
29     cout << "Was asking $" << a_price << endl;
30     cout << "Now asking $" << d_price << endl;
31 
32     outFile << fixed;
33     outFile.precision(2);
34     outFile.setf(ios_base::showpoint);
35     outFile << "Make and model: " << automobile << endl;
36     outFile << "Year: " << year << endl;
37     outFile << "Was asking $" << a_price << endl;
38     outFile << "Now asking $" << d_price << endl;
39 
40     outFile.close();    //程序使用完该文件后，应将其关闭。如果忘记关闭，程序正常终止时将自动关闭它
41 
42     system("pause");
43     return 0;
44 }

 1 #include<iostream>
 2 #include<fstream>//文件I/O
 3 #include<cstdlib>//exit()
 4 using namespace std;
 5 const int SIZE = 90;
 6 
 7 int main()
 8 {
 9     char filename[SIZE];
10     ifstream inFile;//声明ifstream对象
11     cout << "Enter name of data file:";
12     cin.getline(filename, SIZE);
13     inFile.open(filename);//关联文件
14 
15     if (!inFile.is_open())//文件打开失败
16     {
17         cout << "Could not open the file " << filename << endl;
18         exit(EXIT_FAILURE);
19     }
20     double value, sum = 0.0;
21     int count = 0;
22 
23     inFile >> value;
24     while (inFile.good())//输入正确
25     {
26         ++count;
27         sum += value;
28         inFile >> value;
29     }
30     if (inFile.eof())
31         cout << "End of file reached." << endl;
32     else if (inFile.fail())
33         cout << "Input terminated by data misamatch." << endl;
34     else
35         cout << "Input terminated for unknown reason." << endl;
36     if (count == 0)
37         cout << "No data processed." << endl;
38     else {
39         cout << "Items read: " << count << endl;
40         cout << "Sum: " << sum << endl;
41         cout << "Average: " << sum / count << endl;
42     }
43     inFile.close();
44 
45     system("pause");
46     return 0;
47 }