ENGR/CS 101 CS Session
Lecture 3
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Log into Windows/ACENET (reboot if in
Linux)
Start Microsoft Visual Studio 2010
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Lecture 3
Windows button -> All Programs ->
02 Programming -> Microsoft Visual Studio 2010
-> Microsoft Visual Studio 2010
Choose C# as default environment, click Start
Visual Studio button
Wait for a long time... (next time should be faster)
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Outline
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Program specification
Program design
Programming languages
Using MS Visual Studio
C# programming language
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Types and variables
Assignment and expressions
Input and output
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Program Specification
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Work our way up to a GUI program to do the
Caesar shift cipher. Today's console
program will do the following:
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Ask the user for an uppercase key letter (to
represent shift A-> key) and an uppercase letter
to encipher with this shift
Output the corresponding ciphertext letter
Example run (user input in bold):
Enter an uppercase key letter: I
Enter an uppercase letter to encipher: G
The corresponding ciphertext letter is: O
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Program Analysis & Design
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How will the program accomplish the
specifications?
Identify the data being used
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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
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Programming Languages
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Syntax: What are the legal "sentences" in the
language?
Semantics: What do the "sentences" mean?
Compilers and interpreters enforce syntax.
Semantics determine whether the
computation is correct.
A program is not "working" if it gives the
wrong results!
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Compiling vs. Interpreting
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Some languages are compiled with a
program called a compiler. Source code file
is translated into a machine code file.
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Examples: C/C++, Java, Pascal, COBOL, Fortran
Other languages are interpreted. An
interpreter is a program that receives
programming language statements and
executes them directly.
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Examples: (original) BASIC, LISP, Prolog, LOGO
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Source Code to
Running Program
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EDITOR -> source code file
-> COMPILER -> object file (+ libraries)
-> LINKER -> executable file
-> LOADER -> running program
Sometimes programs are run individually;
sometimes all work together in an Integrated
Development Environment (IDE)
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Microsoft Visual Studio
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Microsoft Visual Studio is an IDE for
developing applications for Windows in
multiple programming languages
We will be using C#.
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Creating a Console Project
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All C# code belongs to a project. Start with New
-> Project
Each project produces a particular kind of
application. We will be creating a console
application.
After selecting the console application template,
set the Name box to "cs101console". Make
sure the Location is on your network drive,
then click OK. A large text window and a
Solution Explorer panel will appear.
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New Project Dialog
Make sure this is
on your network
drive!
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C# Programs
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The C# IDE tries to be helpful by creating the
parts of code that all C# program have. This
includes:
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using statements that cause (pre-defined) method
names in libraries like System to become known. (A
method is the same thing as a function.)
namespace and class definition names based on the
project name given.
a stub for the Main( ) method. The main program
code goes in this stub. It is the code that is executed
first when a program is run.
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MS VS Project Window
Project code goes here!
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C# Programming Language
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Developed by Microsoft for .NET framework
Syntax similar to C++ and Java
Semantics similar to Java
Object-oriented - won't cover in this class
Built-in support to make GUIs (Graphical
User Interfaces) - will look at this in next class
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Types and Variables
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A variable is a named memory location that
holds a value. All memory is in bits.
A variable has a type that determines how the
bits are interpreted into a value. Numbers are in
binary. Characters are mapped to binary
numbers. E.g., ASCII or Unicode.
C# types include
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int for integers (e.g., 5, -25, 0)
char for characters (e.g. 'A', 'b', '7', '%')
string (e.g. "Hello!")
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Types and Variables
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Variables are declared by giving type and name
Syntax is: <type> <var1>, <var2>, ..., <varn>;
Examples:
char shiftKey,
plainLetter,
cipherLetter;
int shiftNumber,
index;
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//
//
//
//
//
key letter
user input
result
# of shift places
of cipher letter
// marks the beginning of a comment to the end
of the line
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Assignments and Expressions
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Assignment means to store a value into a
variable.
Syntax is: <var> = <expression>;
The expression is evaluated and the result is
stored in the variable. An expression can be:
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A literal. E.g., 12 or 'A'
A variable. E.g., shiftNumber
A function call. (More on this later.)
An expression of one or more literals, variables, or
function calls.
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Assignments and Expressions
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Examples:
shiftKey = 'I';
plainLetter = shiftKey;
shiftNumber = shiftKey - 'A';
shiftKey = char.Parse(System.Console.ReadLine());
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Computing the Cipher Letter
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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';
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Computing the Cipher Letter
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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;
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The modulus operator symbol is %
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Computing the Cipher Letter
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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);
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Output
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C# output is done by calling a built-in function
that takes a string as an argument. There
are two forms:
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System.Console.Write ( ) - displays string to
screen
System.Console.WriteLine ( ) - displays string to
screen followed by a newline character
Strings can created by concatenating the
items to be displayed using +.
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Output
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Examples:
System.Console.Write
("Enter an uppercase key letter: ");
System.Console.WriteLine
("The corresponding ciphertext letter is: "
+ cipherLetter);
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Input
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C# input is done by calling a built-in function
that has no arguments and returns a string
that contains what the user typed in.
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System.Console.Read( )
Since all 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(System.Console.Read());
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Review:
Program Analysis and Design
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Identify the data and types being
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shift key (char), plaintext letter (char), ciphertext letter
(char), shift number (int), index (int)
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 - more details
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Compute shift number
Compute index of ciphertext letter
Compute the ciphertext letter
4. Output the ciphertext letter to the screen
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Putting the Code Together
// This code goes in the place indicated on Slide 12
// Variable declarations
char shiftKey,
// key letter
plainLetter, // user input
cipherLetter;// result
int shiftNumber, // # of shift places
index;
// of cipher letter
// Get the key letter and a letter to encipher
System.Console.Write("Enter an uppercase key letter: ");
shiftKey = char.Parse(System.Console.ReadLine());
System.Console.Write
("Enter an uppercase letter to encipher: ");
plainLetter = char.Parse(System.Console.ReadLine());
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Putting the Code Together
// Continuation from previous slide
// Compute the corresponding ciphertext letter
shiftNumber = shiftKey - 'A';
index = (plainLetter - 'A' + shiftNumber) % 26;
cipherLetter = (char)((int)'A' + index);
// Display the result
System.Console.WriteLine
("The corresponding ciphertext letter is: "
+ cipherLetter);
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Building a Program
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To build (i.e., compile) the program do Build
-> Build Solution
If there are no syntax errors, great! If there
are syntax errors, they will be listed at the
bottom of the screen. Correct and build
again.
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Running a Program
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To run the
program, do
Debug -> Start
Without
Debugging.
This will start
the console
window and
run the
program.
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