ENGR/CS 101 CS Session Lecture 9 Log into Windows/ACENET (reboot if - - PowerPoint PPT Presentation

ENGR/CS 101 CS Session Lecture 9

 Log into Windows/ACENET (reboot if in

Linux)

 Start Microsoft Visual Studio 2012  Any questions about the exercise from last

time?

Lecture 4 ENGR/CS 101 Computer Science Session 1

Outline

 Problem: Encode a single letter using Caesar

shift cipher

 Substitution Cipher Project

 Textboxes  Getting user input  Computing ciphertext letter  Displaying result

Lecture 4 ENGR/CS 101 Computer Science Session 2

Problem Specification

 Will work our way up to a program to do the

Caesar shift cipher on messages in a file. Today's program will do the following:

 Allow the user to enter a shift key letter in

uppercase

 Allow the user to enter a plaintext letter in

uppercase to be enciphered

 Have a button for the user to click to have the

plaintext letter enciphered

 Display the ciphertext letter

Lecture 4 ENGR/CS 101 Computer Science Session 3

Interface Mockup

 Textboxes to enter

plaintext and shift key, and to display ciphertext

 Button to encipher

plaintext.

 Labels to identify the

textboxes

Lecture 4 ENGR/CS 101 Computer Science Session 4

Create the GUI

 Create a new project. Make sure the

language template is Visual C#.

 Select "Windows Form Application". Give

the project a name like "SubstitutionCipher".

 Make sure the location is on your network

drive.

 Click on OK. You will get the GUI designer

with a blank form. Change the Text property to something like "Substitution Cipher".

Lecture 4 ENGR/CS 101 Computer Science Session 5

Textboxes

 A Textbox is a GUI element that can be used

to get text input from a user. It also can be used to display results. (This is better than a label for larger amounts of output.)

 The text in a Textbox is accessed through the

Text property.

Lecture 4 ENGR/CS 101 Computer Science Session 6

In-class Exercise, Part 1

 Create a simple form with three Textboxes for

the plaintext, ciphertext, and shift key, and a Button for doing the encipher.

 For textboxes containing the plaintext and the

ciphertext, change the Multiline property to

• True. After this, pull on the handles to make

them as large as you like.

 Label and arrange these elements however you

like on the form. Change properties like color and font as you wish.

Lecture 4 ENGR/CS 101 Computer Science Session 7

In-class Exercise, Part 1

 Change the Name properties of the GUI

elements as follows:

 Plaintext textbox is named plaintextBox  Ciphertext textbox is named ciphertextBox  Shift key textbox is named keyBox  Encipher button is named encipherBtn

Lecture 4 ENGR/CS 101 Computer Science Session 8

Program Analysis & Design

 How will the program accomplish the

specifications?

 Identify the data being used

 shift key, plaintext letter, ciphertext letter

 Write the steps of an algorithm

• 1. Get the shift key letter from the user
• 2. Get the plaintext letter from the user
• 3. Compute the ciphertext letter
• 4. Output the ciphertext letter to the screen

Lecture 3 ENGR/CS 101 Computer Science Session 9

Application Data

 Double-click on the Encipher button to

create the handler method stub.

 Unlike the Dot Chaser program, all of the

action happens within the handler when the Encipher button is clicked.

 Declare the application data in the handler

char shiftKey, // key letter plainLetter, // user input cipherLetter; // result

Lecture 4 ENGR/CS 101 Computer Science Session 10

Handler Design

 The specific design of the handler code for the

Encipher button is as follows

• 1. Clear the ciphertext box
• 2. Get the shift key from keyBox.Text
• 3. Get the plaintext letter from plaintextBox.Text
• 4. Compute the ciphertext letter
• 5. Append the cipher letter to the ciphertext box

 Clearing the ciphertext box is simply setting the

Text property of the empty string.

ciphertextBox.Text = "";

Lecture 4 ENGR/CS 101 Computer Science Session 11

Getting User Input

 We will get the user data from the keyBox and

plaintextBox using the Text property like so:

 keyBox.Text  plaintextBox.Text

 Since the input is in the form of a string, it

must be converted to the appropriate type before assignment. Each type has a Parse function for this purpose. E.g.

shiftKey = char.Parse(keyBox.Text); plainLetter = char.Parse(plaintextBox.Text);

Lecture 4 ENGR/CS 101 Computer Science Session 12

Computing the Cipher Letter

 Assume that variable shiftKey holds the key

letter and variable plainLetter holds the letter to be enciphered.

 Since the alphabetic characters have

sequential mapping (i.e., 'A' is first, followed by 'B', etc.), the number of places to shift is the key letter minus 'A'. In C# code, this is:

shiftNumber = shiftKey - 'A';

Lecture 3 ENGR/CS 101 Computer Science Session 13

Computing the Cipher Letter

 To find the cipher letter, we determine the index of

plaintext letter (i.e., where in the alphabet it is when we start counting at 0) using a similar method, then add the shift number.

 This will be the index of the ciphertext letter, except

that the number may be greater than 26. To make it circular, we compute the modulus with respect to

• 26. In code, this is:

index = (plainLetter - 'A' + shiftNumber) % 26;

 The modulus operator symbol is %

Lecture 3 ENGR/CS 101 Computer Science Session 14

Computing the Cipher Letter

 Now we add this new index back to 'A' to find

the ciphertext letter.

 However, C# is strict about types and is

unhappy that we are trying to add a number to a character, so we have to tell the compiler to treat 'A' as a number, then treat the result as a character by casting. The code becomes:

cipherLetter = (char) ((int) 'A' + index);

Lecture 3 ENGR/CS 101 Computer Science Session 15

Displaying the Result

 To display the result, it must be placed in the

Text property of the ciphertext box.

 In preparation for the next phase of the

project, we will do this by concatenating the resulting cipher letter to the ciphertext box Text.

ciphertextBox.Text += cipherLetter;

Lecture 4 ENGR/CS 101 Computer Science Session 16

In-class Exercise, Part 2

 Double-click on the Encipher button to get to

the handler function stub, if you haven't done so already.

 Finish writing the code for the Encipher

button handler. All of the code is shown together on the next two slides.

Lecture 4 ENGR/CS 101 Computer Science Session 17

Encipher Button Handler Code

// Application data char shiftKey, // key letter plainLetter, // user input cipherLetter; // result int shiftNumber, // # of shift places index; // of cipher letter // Clear the ciphertext (result) box ciphertextBox.Text = "";

Lecture 4 ENGR/CS 101 Computer Science Session 18

Encipher Button Handler Code

// Get the key letter and a letter to encipher shiftKey = char.Parse(keyBox.Text); plainLetter = char.Parse(plaintextBox.Text); // Compute the corresponding ciphertext letter shiftNumber = shiftKey - 'A'; index = (plainLetter - 'A' + shiftNumber) % 26; cipherLetter = (char)((int)'A' + index); // Display the result // Append the enciphered letter to ciphertext box ciphertextBox.Text += cipherLetter;

Lecture 4 ENGR/CS 101 Computer Science Session 19

Test the Program

 When you have competed writing the handler

code, try running it with different keys and input.

 What happens if you try to input an entire

word in the plaintext box?

 Next class we will enhance the project to

handle encoding an entire word.

Lecture 4 ENGR/CS 101 Computer Science Session 20