Download streams4.2B

Start
File Streams
03/04/11
Stream as Connection to I/O
Example of Creating a Stream
 Program
that outputs a quote to a file
 writefile.cpp
To Connect Stream to File
•
Header File
#include <fstream>
•
Declare stream & open file
ifstream fs_in(“mydata”, ios::in);
ofstream fs_out(“myout”, ios::out);
To Connect Stream to File
3. Input/Output
fs_in >> x;
fs_out << “Hello>\n”;
4. Close
fs_in.close( );
fs_out.close( );
Example of Input
 Write
a program to input a list of positive
numbers from a file, then output the sum.
– Create stream and connect to file.
– Input number from input stream
– While number not negative
– Add number to sum
– Input number from input stream
– Output sum
– Close stream
streams4.2/sum.cpp
Another Problem
Start Here
 Write
a program to input a file of five
temperatures in degrees Celsius. Convert
the temperatures to Fahrenheit and output
them to another file. Use a function to do
the conversion.



What would the algorithm be?
Let's write the program.(f = 9/5c + 32)
celsius.txt
Sentinel Data in a File
 Value
that is not part of the data marks the
end of a list.
 I am going to use '*' as a sentinal to mark
the end of data in some character input in
the next example.
Caesar Cipher
 Using
the Caesar Shift (2 to the right), the
message.
 "RETURN TO ROME"
would be encrypted as,
"TGVWTP VQ TQOG"
 Essentially, add +2 to the ascii value of a
character.
 To decode shift it back by -2
Caesar Cipher
 When
using cin with characters, spaces are
skipped.
 cin.get() inputs the spaces, too.
Caesar Cipher
 Write
a program that inputs a message
from the keyboard and saves the coded
version in a file called code.txt
 Stop input when the sentinel, '*', is found.
 cipher2.cpp uses a cin.get() so that spaces
won't be skipped.
Exercise
 p.
122, #2
 Read sec. 7.3 for Friday.