01: #include <string>
02: #include <iostream>
03: #include <fstream>
05: using namespace std;
06: 
07: /**
08:    Reads numbers from a file and finds the maximum value
09:    @param in the input stream to read from
10:    @return the maximum value or 0 if the file has no numbers
11: */            
12: double read_data(istream& in)
13: {  double highest;
15:    double next;
16:    if (in >> next) highest = next;
18:    else return 0;
20: 
21:    while (in >> next)
23:       if (next > highest) highest = next;
27:    return highest;
28: }
29: 
30: int main()
31: {  double max;
33: 
34:    string input;
35:    cout << "Do you want to read from a file? (y/n) ";
36:    cin >> input;
37: 
38:    if (input == "y")
39:    {  string filename;
41:       cout << "Please enter the data file name: ";
42:       cin >> filename;
43: 
44:       ifstream infile;
45:       infile.open(filename.c_str());
46: 
47:       if (infile.fail()) 
48:       {  cout << "Error opening " << filename << "\n";
50:          return 1;
51:       }
52: 
53:       max = read_data(infile);
54:       infile.close();
55:    }
56:    else max = read_data(cin);
58: 
59:    cout << "The maximum value is " << max << "\n";
61:    return 0;
62: }