File I/O

• A file is a collection of data stored on the disk
• We may wish to read from a file
• We may wish to create a file.
• This is very close to the I/O we have been doing.
  • We need an additional header: #include <fstream>
  • We need a new type
    • ifstream inputfile;
    • ofstream outputfile;
  • We need to open the files
    • inputfile.open("myfile"); // open for input
    • outputfile.open("newfile"); // open for output
    • CAUTION: opening an output file erases any existing file by that name.
  • We need to read from/ write to the files.
    • inputfile >> avar; // read avar from the input file.
    • outputfile << aver; // wwrite avar to the output file.
  • We should close them when we are done.
    • inputfile.close();
    • outputfile.close();
  • All of the rules for I/O that we have learned still apply, (reading the wrong values and such)
  • Open takes a C string not a C++ string.
    • C strings come in 131
    • For now:

      string   filename;
      ifstream infile;
      
      cout << "Enter the name of your input file: ";
      cin >> filename;
      cout << " Opening " << filename << " for input." << endl;
      infile.open(file.c_str());
      	    

Assume a person's information is stored in a datafile, write a program that will read this information and print a formatted copy to the screen and to a file. You should prompt for the input and output file names.

The file format is :

name name birth day occupation height weight

Example Input:

Smith John 10/10/80 Student 5'10 180

Sample Output:

John Smith,
     Born: 10/10/80
     Occupation: Student
     Height:   5'10, Weight 180

Program Design

• Object Oriented Desgn: A technique for developing software in which the solution is expressed in terms of objects (self containted entities composed of data and operations on that data)
• Functional Decompisition: A technique for developing software in which the problem is divided into more easily handled subprograms, the soultions of which create a solution to the overall problem.
• OOP -start at the bottom and work your way up.
• FD - start at the top and work your way down.
• C++ is an Object Oriented Language.
• You have seen some of this
  • ifstream infile;
  • string filename;
  • infile.open(filename.c_str());
• You will see MUCH more in 131
• Read pages 173 - 182
• Object Oriented Design
  • Create objects that solve small problems.
  • You can use existing classes, or create your own.
  • You may even derive new classes from old ones.
  • We need more C++ to be able to do this correctly.
• Functional Decompisition
  • Try breaking the program into a series of steps.
  • Each step is either simple, code it, or complex
  • Break the complex steps down further.
  • Structure chart.
  • 
  • Zimmer's Program Guidelines

Two more programming problems for the day: Both are from Essential C++ for Engineers and Scientists from Jeri R Hanly.

• Write a program that predicts the score needed on a final exam to achieve a desired grade in a course. The program should interact with the user as follows:

   Enter desired grade=>
   Enter minimum average required for a _=>
   Enter your current average in the course=>
   Enter how much the final counts as a percentage of the course grade=>
  
   You need a score of __.__ on the final to get a _.
  

• Metro City Planner, Inc. proposes that a community conserve its water supply by replacing all the community's toilets by low-flush models that use only 2 leters of water per flush. Assume that there is about 1 tolet for every 3 persons, that existing toilets use an average of 15 leters per flush, that a toilet is flushed on average of 14 times per day, and that the cost of installing a new toilet is $150. Write a program that would estimate the magnitude (liters/day) and cost of the water saved based on the commuity's population.