CSCI 261 - Programming Concepts - Lab 6B

CSCI 261 - Programming Concepts (C++) Fall 2017 - Lab 6B Quick Links: Canvas \| CS @ Mines \| Cloud9 \| Piazza \| zyBooks
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This lab is due by Friday, November 10, 2017 11:59 PM . Concepts The focus of this assignment is on one concept: how to read data from an "input file stream" or ifstream object. Working with Data Today's class discussed how data is often treated as "streams" of information that can be read a piece at a time. The files we will read in CSCI 261 are simple text files; for lab today, the simple text file contains a series of characters. Remember that whenever you work with a file stream as input, we call them `ifstream` objects. There will always be four things you will do whenever working with an `ifstream` . Open the file, check for an error, read its data, and close the file. The typical pattern for this is as follows: #include <iostream> #include <fstream> using namespace std; int main() { int age; ifstream myCatsAges("filename"); // declare ifstream object and open the file // check for an error if ( myCatsAges.fail() ) { cerr << "Error opening input file"; exit(1); } // read the data and do something with it while ( !myCatsAges.eof() ) { myCatsAges >> age; cout << "One cat is " << age << " years old.\n"; } myCatsAges.close(); // close the file return 0; } Remember, once you have an `ifstream` object (like `myCatsAges` shown above) you use it in a manner similar to using `cin` . Instructions The cows have been kidnapped by aliens! The only clue to their whereabouts is a strange "ciphered" message, stored in the file secretMessage.txt. Fortunately, our in-house cryptanalysis expert, D. Cipher, has discovered the key: "The key isn't very advanced, mmmkay? To decipher the message," she says, " you should take each character and replace all `~` (tilde) characters with a space, and shift all characters up by one, mmmkay?" Your goal for this assignment is to create a program that reads the ciphered text file and then writes a deciphered version to a file called `decipheredMessage.txt` . For each character in the file, your program should implement the following replacement algorithm: If the character read is a newline character `'\n'`, then you should write the newline character to the file. Otherwise, if the character read is a `~`, you should write a space to the file. Otherwise, write the character read "offset" by +1. To see if your implementation works, you should be able to open the file `decipheredMessage.txt` and see the information about the missing cows. Hints Where to place the input file Any input file needs to be placed at the project level, which should be the same directory as your `main.cpp` file. You should see both your input file AND main.cpp file in the same directory. Reading whitespace characters In order to capture and replace whitespace characters, you will not use the `>>` operator with the input filestream. Instead, you will use the `get()` function like this: while ( secretMessage.get(c) ) { // ...mmkay } This example assumes your `ifstream` is called `secretMessage` and you have a `char` variable declared that is called `c` . Selection statement Note that one requirement is to model the logic of the deciphering algorithm using a proper `if/else-if/else` construct. A `switch` statement could also be used. Casting to `char` Remember, `cout` and `ofstream` objects are sensitive to the datatype of the value to be printed or written to a file. Consider the following: cout << ('a' + 2); What is printed to the screen? The number 99. Why? Because a `char` plus an `int` yields an `int` , and then the int is "sent" to `cout` . To print the character `c` to the screen, you will need to use casting, like this: cout << char('a' + 2); Ahhh, much better. Lab Submission You will submit your solution to this lab with the rest of A6. Detailed instructions for doing this are posted in Assignment 6. This lab is due by Friday, November 10, 2017 11:59 PM .
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