ENGR/CS 101 CS Session Lecture 3

Transcription

1 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 > 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

2 Registration Session The registration session has been moved to next class, Wednesday, November 2 (instead November 7 in the syllabus) Students should try to pre-register for courses. Guidebooks are available in EECS office. Students will meet in groups based on major: CS students - KC-267 with Dr. Hwang CoE students - KC-137 with Dr. Mitchell EE students - KC-136 with Dr. Howe Lecture 3 ENGR/CS 101 Computer Science Session 2

3 Outline Program specification Program design Programming languages Using MS Visual Studio C# programming language Types and variables Assignment and expressions Input and output Lecture 3 ENGR/CS 101 Computer Science Session 3

4 Program Specification Work our way up to a GUI program to apply the Vigenere cipher to a text file. 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 Lecture 3 ENGR/CS 101 Computer Science Session 4

5 Program 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 5

6 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! Lecture 3 ENGR/CS 101 Computer Science Session 6

7 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 Lecture 3 ENGR/CS 101 Computer Science Session 7

8 Source Code to Running Program EDITOR -> programming language source 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) Lecture 3 ENGR/CS 101 Computer Science Session 8

9 Microsoft Visual Studio Microsoft Visual Studio is an IDE for developing applications for Windows in multiple programming languages, including C#. Free Express versions of each individual compiler are available. Link to the download page on the CS session webpage. EECS students can get the full version through UE's MS Alliance program (see Jeff Cron). Lecture 3 ENGR/CS 101 Computer Science Session 9

10 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. Lecture 3 ENGR/CS 101 Computer Science Session 10

11 New Project Dialog Make sure this is on your network drive! Lecture 3 ENGR/CS 101 Computer Science Session 11

12 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 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. Lecture 3 ENGR/CS 101 Computer Science Session 12

13 MS VS Project Window Project code goes here! Lecture 3 ENGR/CS 101 Computer Science Session 13

14 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 next class Lecture 3 ENGR/CS 101 Computer Science Session 14

15 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!") Lecture 3 ENGR/CS 101 Computer Science Session 15

16 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 Lecture 3 ENGR/CS 101 Computer Science Session 16

17 Assignment 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. Lecture 3 ENGR/CS 101 Computer Science Session 17

18 Assignment and Expressions Examples: shiftkey = 'I'; plainletter = shiftkey; shiftnumber = shiftkey 'A'; shiftkey = char.parse(system.console.readline()); Lecture 3 ENGR/CS 101 Computer Science Session 18

19 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 19

20 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 20

21 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 21

22 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 +. Lecture 3 ENGR/CS 101 Computer Science Session 22

23 Output Examples: System.Console.Write ("Enter an uppercase key letter: "); System.Console.WriteLine ("The corresponding ciphertext letter is: " + cipherletter); Lecture 3 ENGR/CS 101 Computer Science Session 23

24 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()); Lecture 3 ENGR/CS 101 Computer Science Session 24

25 Review: Program Design Identify the data being used - what are their types? 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 Lecture 3 ENGR/CS 101 Computer Science Session 25

26 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 from user 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()); Lecture 3 ENGR/CS 101 Computer Science Session 26

27 Putting the Code Together // 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); Lecture 3 ENGR/CS 101 Computer Science Session 27

28 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. Lecture 3 ENGR/CS 101 Computer Science Session 28

29 Running a Console Program To run the program, do Debug -> Start Without Debugging. This will start the console window and run the program. Lecture 3 ENGR/CS 101 Computer Science Session 29