CMPT-101. CMPT-101-D2, Spring Course Web Page Course Mailing List. Exams. Assignments

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1 CMPT-101 CMPT-101-D2, Spring 2000 Week 1, Introduction Instructor: Toby Donaldson An introduction to programming and computer science Covers the basic ideas used in (most) major general-purpose programming languages 1 2 Course Web Page The cmpt-101 web page is the main source of information Course outline and schedule Assignments posted there Two important things to do right away: Learn how to download and read PDF files Print and read Russ Tront s guide to Borland C++ (it's a PDF file!) 3 Course Mailing List You are all automatically added to an electronic mailing list Only me and the TAs can send to it The list is archived on the web page Important information (e.g. corrections to assignments) will be posted here Read your regularly! 4 Assignments 5 individual programming assignments 1 project, in teams of up to 3 people Deadlines are strict: no individual extensions computers always seem to crash at the worst possible time, so aim to be finished 2 days before the deadline 5 Exams Exams will be open book You may use the textbook, your notes, or any other reference materials --- even your own brain!! But no electronic devices! Midterm: Wednesday, Feb. 23 (in class, 50 minutes) Final exam: Monday, April 19, 3:30pm 6:30pm (location TBA, 3 hours) 6

2 Two Sections This is CMPT-101-D2 You are the morning section There is also an afternoon section You are not the afternoon section! You must write the proper exams! Different sections have different exams! But assignments are all the same Are the Lectures the Same? Not in minute to minute detail, but the same schedule will be followed You should attend the lecture for the section you are registered in Exams can test anything from the lectures for your section! 7 8 Assignment Lab Accounts All registered students have accounts in the assignment lab ID is same as your Unix ID, and password is initially the first seven digits of your student number If you registered late, go to AQ3143 with your name,unix ID, and student number Grant Dimock or Don Seeley will give you an account Borland C++ (BC++) Use version 5 or higher You can use a different C++ compiler at your own risk! Again: download and read Russ Tront s guide to BC++ BC++ is an integrated development environment (IDE) 9 10 Course Textbook Buy this: we'll be following it roughly one chapter per week It comes with special C++ code that we'll be using Appendix A1: coding style guidelines Appendix A2: C++ summary Other Books The other books on the course outline may be useful to you I recommend that you use at least two books, e.g.: The course textbook A C++ reference book (e.g. the Deitel and Deitel book is a good one) 11 12

3 This is probably the best general C++ reference Written by C++'s creator Warning: not for beginners; I don't recommend this if you haven't programmed before! 13 Bjarne Stroustrup C++ s Designer a programming language is really only a very tiny part of the world, and as such, it ought not to be taken too seriously. Keep a sense of proportion - and most importantly - keep a sense of humor. Among major programming languages, C++ is the richest source of puns and jokes. This is no accident. 14 Deitel and Deitel Useful as a C++ reference Has lots of examples showing how to use features of C++ A lot of point-bypoint summaries Not actual size Some students like this book It has exercises with answers Simple, English explanations Warning: leaves out a few aspects of modern C Every Journey Begins with a Single Step In computer science (CS), the first step is to learn the basics of programming a computer CS is the study of programmable machines Even if you leave CS, programming is a useful (and lucrative!) skill The C++ Programming Language In this course, all the programming will be done in C++ C++ is currently the premier generalpurpose programming language Much (most?) store-bought PC software is written in C++ C++ is big, messy, and complex 17 18

4 Why C++? C++ is Practical Powerful Popular We won't (can't!) go into all the details of C++ Only the most fundamental parts Later courses will cover more advanced features 19 C++ Facts Designed by Bjarne Stroustrup starting in the early 1980s Originally called C with classes Based on C, a lower-level language developed in the 1970s C++ is, practically, a superset of C C++ improves upon many features of C C programmers take note: you will need to unlearn many C programming habits! 20 C++ is General Purpose C++ is practical for many different kind of applications, e.g. operating systems, compilers, databases, graphics, etc. We won't use all of C++'s features; some are Advanced, e.g. templates and inheritance Ensure backwards compatibility with C, e.g. malloc Application specific, e.g. valarray is for numeric processing 21 Learning C++ C++ is a complex, real-world language Need to master many technical details Getting your first program running can be a challenge! Need to know how to use your computer, e.g. creating, copying, deleting files Borland C++ runs under DOS and Windows (95/98/NT) 22 Three Keys to Programming Practice, practice, practice! Write and understand as many (small) programs as you can Re-read the previous point Even experienced programmers need to keep in practice Other things help: experience, knowledge, dedication, imagination, organizational skills, common sense, A First C++ Program The traditional first program to write is one that prints the words Hello, world!on the screen C++ provides a standard way to read and write characters to and from the screen problem solving ability, etc

5 The User (a human) Some Important Objects Screen cout Keyboard cin C++ program The screen and keyboard are the two most common I/O devices, and for this course they will be the main way that a program interacts with the outside world. 25 C++ Input/Output Names The standard output object is named cout Means "console output" The standard input object is named cin Means "console input" cin and cout are for character-based I/O (can t do graphics with them) 26 Hello World! // hello1.cpp // Prints "Hello, world! " on // one line on the screen #include <iostream.h> int main() { cout << "Hello, world!\n"; } 27 Hello Bonnie! // hello2.cpp #include <iostream.h> #include <string> int main() { string name("bonnie"); cout << "Hello, " << name << \n ; } 28 Hello Somebody! // hello3.cpp #include <iostream.h> #include <string> int main() { string name; cout << "What is your name?\n"; cin >> name; cout << "Hello, " << name << \n ; } 29 Hello Bonnie and Clyde! // hello4.cpp #include <iostream.h> #include <string> int main() { string first_name; string second_name; cout << "Enter 2 names (separated by a space): "; cin >> first_name; cin >> second_name; cout << "Hello, " << first_name << " and " << second_name << \n ; } 30

6 One Plus One // oneplusone.cpp #include <iostream.h> int main() { cout << "1 plus 1 is " << (1+1) << \n ; } 31 X plus Y // xplusy.cpp #include <iostream.h> int main() { cout << "Please enter an int: "; int x; // declares the variable x; has a junk value cin >> x; cout << "Please enter another int: "; int y; cin >> y; cout << x << " plus " << y << " is " << (x+y) << \n ; } 32 Programs and Algorithms A program implements an algorithm Programs are sometimes referred to as implementations A program must be written in a particular programming language (like C++) CMPT-101 teaches basic methods for implementing algorithms 33 Algorithms An algorithm is a description of a step by step process Every step must be precisely understood An algorithm takes input and produces output An algorithm is an abstract idea, and the same algorithm can have many different implementations 34 How do You do Laundry? Making Change Write an algorithm for doing the laundry Take out your pocket change, and make two piles of equal value; try it now! 35 36

7 When is Easter? The Gregorian Calendar At the first council of Nicaea (A.D. 325) it was decided that Easter would be the first Sunday after the first full moon after the vernal equinox Different calendars calculate Easter (and other dates) in different ways We'll stick to the traditional Western calendar 37 In 1582, Pope Gregory XIII introduced the calendar we still use today The previous calendar is the Julian calendar A main reason for this new calendar was to make Easter occur in spring! A Julian year is slightly longer than an actual year 38 When is Easter? Calculating what day of the year Easter occurs on is surprisingly difficult We'll look at an algorithm for determining Easter, given a particular year We won't worry about how this algorithm was discovered, just how it can be implemented in C++ 39 Easter Dates, 1900 to 1943 Year Date Year Date Year Date / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /25 40 Easter Dates, 1944 to 1988 Easter Dates, 1989 to 2033 Year Date Year Date Year Date / / /21 Year Date Year Date Year Date / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /17 42

8 Easter Dates, 2034 to 2078 Easter Dates, 2079 to 2099 Year Date Year Date Year Date / / / / / / / / / / / / / / / / / / / / /29 Year Date Year Date Year Date / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / An Easter Algorithm What day will Easter fall on in the year 2085? Answer: March 22 Here is an algorithm that will give the date of Easter for any year from 1900 to An Easter Algorithm Step 1: Call the year Y. Subtract 1900 from Y and call the difference N. Step 2: Divide N by 19. Call the remainder A. Step 3: Divide (7A+1) by 19. Ignore the remainder and call the quotient B. Step 4: Divide (11A+4-B) by 29. Call the remainder M. Step 5: Divide N by 4. Ignore the remainder and call the quotient Q. Step 6: Divide (N+Q+31-M) by 7. Call the remainder W. Step 7: The date of Easter is 25-M-W. If the result is positive, the month is April. If it is negative, the month is March. 0 means March 31, -1 means March 30, -2 as March 29 and so on to -9 for March Algorithm Execution You can "run" this algorithm by hand You can write the intermediate values on a piece of paper, or just remember them The inventor of this algorithm claims he used it as a party trick! Usually a good idea to try an algorithm by hand Easter 1999 is April 4th Y = 1999 N = Y = = 99 A = N mod 19 = 99 mod 19 = 4 B = (7A + 1) div 19 = 29 div 19 = 1 M = (11A B) mod 29 = 47 mod 29 = 18 Q = N div 4 = 99 div 4 = 24 W = (N + Q M) mod 7 = 136 mod 7 = 3 E = 25 - M - W = = 4 48

9 Easter 2000 is April 23rd Y = 2000 N = Y = = 100 A = N mod 19 = 100 mod 19 = 5 B = (7A + 1) div 19 = 36 div 19 = 1 M = (11A B) mod 29 = 58 mod 29 = 0 Q = N div 4 = 100 div 4 = 25 W = (N + Q M) mod 7 = 156 mod 7 = 2 E = 25 - M - W = = 23 Writing a Program Our goal is to convert the Easter algorithm into a C++ program We will do this in multiple steps, each more refined than the next First, let's imagine how we would like our program to look on the computer's screen Sample Easter Program Screen Please enter a year from 1900 to 2099 (inclusive), and I will tell you the date for Easter: 1999 In 1999, Easter Sunday is April 4th. Discussion For now, assume that the user enters a legal integer But nothing stops them from entering a string like "nineteen ninety nine" If a year outside the range is entered, an error message should be printed Note that the Easter algorithm says nothing about invalid input, but our program must Designing a Solution Flowcharts Before programming the algorithm in C++, it's always a good idea to design the program in a language other than C++ We will mainly use pseudocode, which is an English-like way of describing algorithms There are other methods, for instance... A pictorial way to represent algorithms Run Easter algorithm on Year Print Easter date on screen Yes Get Year from user Is Year from ? No Print error mesage on screen 53 54

10 Flowcharts A diamond represents a decision Each box can represent multiple statements Flowcharts are impractical for anything but small programs Other pictorial design methods exist, especially in object-oriented design Pseudocode Pseudocode is a structured English description of an algorithm This is starting to look like C++ code, but we don't (yet) worry about all the details of C++ Good pseudocode clearly details the important parts of a program Easter Program Pseudocode Get Year from user If Year not in the range then Print an error message Else Run the Easter algorithm on Year Print the date of Easter to the screen End if Pseudocode Notes The indentation is important; it shows independent blocks of code The "if-structure" consists of two code blocks, only one of which is executed The "End if" tag marks the end of the "else" part of the if-structure Pseudocode is very important --- get into the habit of using it! Pseudocode to C++ Getting the Year Our goal is to translate the Easter pseudocode into C++ code We will not do this all at once, but instead we'll do it step by step This is called top-down stepwiserefinement We will use this method again and again throughout the course 59 We will ask the user to enter a year We will store this as an int in the variable Year int Year; cout << "Please enter a year from " << "1900 to 2099 (inclusive): "; cin >> Year; 60

11 Notes on ints The line int Year; declares Year to be a variable of type int It's initial value is unknown --- it could be any int value at all In BC++, ints are 32 bits long Other versions of C++ may differ 61 An int in Memory Year Year refers to a memory location that is interpreted as an integer. The exact encoding may differ depending on your C++ compiler, but positive ints are usually just binary numbers. Negative ints are usually represented in a special complement form. C++ programmers usually need not worry about these details. 62 Checking for a Valid Year We want to print an error message if Year is out of range In other words, we check if this is true: (Year < 1900) or (Year > 2099) If it is, we print an error message; otherwise, we run the Easter algorithm The if-statement The if-statement lets us make decisions if ((Year < 1900) or (Year > 2099)) { cout << "Oops! You entered an invalid year!\n"; } else { // Easter algorithm goes here } // if Notes on the if-statement This is an if-else statement The logical expression (Year < 1900) or (Year > 2099) is called the condition of the if-statement In BC++, or is not recognized as a keyword, although it is legal C++ You can use instead of or, && instead of and,! instead of not 65 Code Blocks A block of code begins with a { and ends with a } This is how C++ groups multiple statements together Every new code block should be indented See style guide in Appendix A1, and on web page (in slightly modified form) 66

12 What We Have So Far int Year; cout << "Please enter a year from " << "1900 to 2099 (inclusive): "; cin >> Year; if ((Year < 1900) or (Year > 2099)) { cout << "Oops! You entered an invalid year!\n"; } else { // Easter algorithm goes here } // if What Next? We need to put the Easter algorithm in the else part of the if-statement This still requires some work The finished code goes inside main, and includes any necessary files (we need at least iostream) This is easier, so let's do it first C++ Program Template #include <iostream.h> int main() { // code goes here } // main Notes Any program that uses cin or cout must include <iostream> or <iostream.h>, depending on your C++ compiler main is a special function that returns an int In some books you might see void main, but that's technically wrong (although some C++ compilers accept it!) C++ Style The programs presented in lecture are often simplified so they fit onto slides For your own programs, follow the textbook style The web page contains a slightly modified version of the coding guidelines given in appendix A1 of the textbook The Easter Algorithm Now let's write the basic Easter algorithm in C++ In C++ The mod operator is % e.g. (22 % 7) is 1, (22 % 5) is 2, (22 % 8) is 6,... The div operator is / e.g. (22 / 7) is 3, (22 / 5) is 4, (22 / 8) is 2,

13 The Easter Algorithm in C++ So When is Easter? int N = Year ; int A = N % 19; int B = (7*A + 1) / 19; int M = (11*A B) % 19; int Q = N / 4; int W = (N + Q M) % 7; int Easter = 25 - M - W; 73 To figure out the day of Easter, we must follow these rules: If Easter <= 0, then it's on March (Easter+31) If Easter > 0, then it's on April (Easter) We use another if-statement here Easter Algorithm if (Easter <= 0) { cout << "In " << Year << ", " << "Easter occurs on March " << (Easter + 31) << \n ; } else { cout << "In " << Year << ", " << "Easter occurs on April " << Easter << \n ; } // if 75 A Complete Program That's it --- if you put all the pieces together in the right order, you have a C++ program that calculates Easter for any year from 1900 to 2099 Now you should test the program and ensure that its output matches the correct dates (as given on the earlier Easter date lists) 76 Testing a Program Testing Testing a program is simple but timeconsuming: give it some input and check that it produces the correct output This means you need to know the correct output ahead of time You must work out the correct output by hand, or somehow know it in advance When testing, try values that are Extreme, i.e. at the ends of the legal input ranges Ordinary Invalid Be a gorilla when you test programs: try hard to break them! 77 78

14 When it Works When it s All Done When you've done a good job of testing your program, and it works properly, then you might want to spruce it up For instance, you could make it more user-friendly by adding more on-screen instructions, or making the formatting neater, etc. But don't do this until your program works! 79 TAKE A BREAK!!! 80

3. Simple Types, Variables, and Constants

3. Simple Types, Variables, and Constants This section of the lectures will look at simple containers in which you can storing single values in the programming language C++. You might find it interesting