ENGR/CS 101 CS Session Lecture 3 - University of Evansvilleuenics.evansville.edu/~hwang/f12-courses/engrcs101/lecture03-slide… · Examples: C/C++, Java, Pascal, COBOL, Fortran Other

ENGR/CS 101 CS Session

Lecture 3

Log into Windows/ACENET (reboot if in

Linux)

Start Microsoft Visual Studio 2010

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)

Lecture 3 ENGR/CS 101 Computer Science Session 1

Outline

Program specification

Program design

Programming languages

Using MS Visual Studio

C# programming language

Types and variables

Assignment and expressions

Input and output


Program Specification

Work our way up to a GUI program to do the

Caesar shift cipher. Today's console

program will do the following:

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


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


Programming Languages

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!


Compiling vs. Interpreting

Some languages are compiled with a

program called a compiler. Source code file

is translated into a machine code file.

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.

Examples: (original) BASIC, LISP, Prolog, LOGO


Source Code to

Running Program

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)


Microsoft Visual Studio

Microsoft Visual Studio is an IDE for

developing applications for Windows in

multiple programming languages

We will be using C#.


Creating a Console Project

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.


New Project Dialog


Make sure this is

on your network

drive!

C# Programs

The C# IDE tries to be helpful by creating the

parts of code that all C# program have. This

includes:

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.


MS VS Project Window


Project code goes here!

C# Programming Language

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


Types and Variables

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

int for integers (e.g., 5, -25, 0)

char for characters (e.g. 'A', 'b', '7', '%')

string (e.g. "Hello!")


Types and Variables

Variables are declared by giving type and name

Syntax is: <type> <var1>, <var2>, ..., <varn>;

Examples: char shiftKey, // key letter

plainLetter, // user input

cipherLetter; // result

int shiftNumber, // # of shift places

index; // of cipher letter

// marks the beginning of a comment to the end

of the line


Assignments and Expressions

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:

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.


Assignments and Expressions

Examples: shiftKey = 'I';

plainLetter = shiftKey;

shiftNumber = shiftKey - 'A';

shiftKey = char.Parse(System.Console.ReadLine());


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:




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 %



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);


Output

C# output is done by calling a built-in function

that takes a string as an argument. There

are two forms:

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 +.


Output

Examples: System.Console.Write

("Enter an uppercase key letter: ");

System.Console.WriteLine

("The corresponding ciphertext letter is: "

+ cipherLetter);


Input

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.

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());


Review:

Program Analysis and Design

Identify the data and types being

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 Compute shift number

Compute index of ciphertext letter

Compute the ciphertext letter

4. Output the ciphertext letter to the screen


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());


Putting the Code Together

// Continuation from previous slide

// Compute the corresponding ciphertext letter


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

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

// Display the result

System.Console.WriteLine

("The corresponding ciphertext letter is: "

+ cipherLetter);


Building a Program

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.


Running a Program

To run the

program, do

Debug -> Start

Without

Debugging.

This will start

the console

window and

run the

program.


Documents

ENGR/CS 101 CS Session Lecture 3 - University of Evansvilleuenics.evansville.edu/~hwang/f12-courses/engrcs101/lecture03-slide… · Examples: C/C++, Java, Pascal, COBOL, Fortran Other