1. 1 EECS230 Course Introduction and a First Program Ying Wu Electrical Engineering and Computer Science Northwestern University yingwu@ece.northwestern.edu EECS230 Lectures Series

2. 2 Course Personnel Instructor: Ying Wu TA: Ming Yang (m-yang4@northwestern.edu) TA: David Choffnes (drchoffnes@northwestern.edu)

3. 3 Course Information Lectures –M,T,W,F 1-1:50pm, Tech. LR4 –Tuesday meetings: TA sessions Text –C++ How to Program, 4 rd (or later) Edition, by H.M. Deitel and P.J. Deitel, Prentice Hall. Course Web –http://www.courses.northwestern.edu/ using your IDhttp://www.courses.northwestern.edu/ Grading –Machine Problems (MPs):30% –Midterm exam: 30% –Final exam:40%

4. 4 Why should we study programming? Think about your new role in 5 years –A graduate student –An engineer –A manager – … Programming practice can –Implement your ideas –Motivate you to re-think your ideas –Make you solid, sharp and deep-thinking –Make you more cooperative

5. 5 Eager to Learn C/C++? We shall cover –C/C++ control structures –Function –Pointers and Array –Stream I/O and string operations –Dynamic memory allocation –Classes –Classes with pointer data members –Linked list –Sort and search See the course syllabus for a detailed schedule

6. 6 We’ll focus on Core C/C++ concepts –Such as: Pointers and references Call-by-value v.s. call-by-reference Class Copy constructor … Program design Debugging skills

7. 7 The best way in learning C/C++ Deep understanding the concepts, especially –Pointers/references –Functions –Classes Coding experiences –Do spend time in coding –Reading examples Debugging –Tools –Skills

8. 8 The GOAL for Week-1/2 Understand all C/C++ data types Understand basic computer architecture and addressing mechanism Use cin/cout to input/output Grasp six C/C++ control structures Understand array Design by using flowcharts Get a sense of the compiling process DEBUG_1: debugging when you are coding Do the MP#1 (basic control structures)

9. 9 What to learn today? How does the computer do with my code? What are “int”, “float”, “double”, “bool”? What is a variable? What will happen if you declare a variable? Arithmetic expressions and calculation? Logical expressions and decision making? How to get inputs and output results?

10. 10 What does the Computer do with my program? Phases of C++ Programs: 1.Edit 2.Preprocess 3.Compile 4.Link 5.Load 6.Execute Loader Primary Memory Program is created in the editor and stored on disk. Preprocessor program processes the code. Loader puts program in memory. CPU takes each instruction and executes it, possibly storing new data values as the program executes. Compiler Compiler creates object code and stores it on disk. Linker links the object code with the libraries, creates a.out and stores it on disk Editor Preprocessor Linker CPU Primary Memory........................ Disk Let’s see an example then.

11. 11 Basic Data Types int –integer(4 bytes = 32 bits) float –real decimal number (4 bytes = 32 bits) double –double precision real decimal number (8 bytes = 64 bits) char –character (1 byte = 8 bits) bool –true/false (1 byte), or 0/1

12. 12 ASCII char set American Standard Code for Information Interchange A character has a numerical representation (a decimal integer) in computer, e.g., ‘a’ – 97, ‘A’ – 65, ‘1’ – 49, ‘+’ – 43, etc Check the appendix B of D&D for the table Question: how many characters can we have?

13. 13 Conversion among Data Types Priority order –bool and char < int < float < double The compiler can automatically convert low priority data to higher ones But it can not do the inverse automatically Why? –You will lose precisions! So, you have to do it yourself forcefully –e.g., (int) 3.1415  3

14. 14 What is a variable? Three Properties –Type determines the number of bytes of memory that are allocated for this variable by O/S –Name is used to address (or retrieve) this variable in system memory stacks –Value is the content and is used for calculation

15. 15 Memory Concepts Variable names –Correspond to locations in the computer's memory –Every variable has a name, a type, and a value –Whenever a new value is placed into a variable, it replaces the previous value –Reading variables from memory does not change them A visual representation integer1 45

16. 16 Addressing? Physically, each byte of physical memory is a set of registers, each of which corresponds to 0/1. Each byte of memory has a unique “address”. Generally, we use a hexadecimal number to describe its address, e.g., 0x0012FD8C (32 bits) –Question: how many bytes can a 32-bit machine manage? In hardware, addressing is realized by sending such a hexadecimal number to the BUS to get the value of the memory blocks. In C/C++ language, we do not need deal with such hexadecimal numbers, instead, we deal with the names or pointers of variables.

17. 17 What if you declare a variable? O/S will allocate (reserve) a memory block to hold the value of the variable. The value can be changed by “assignment” The value can be retrieved by “addressing” No other variables can use such a memory block until you let the O/S to recycle it. (how?)

18. 18 Examples a = 3;a 3 int a;aa = 5;a 5 float b;a 5 b b = a+1;a 5 b 6

19. 19 Arithmetic Expressions Arithmetic calculations –Use * for multiplication and / for division –Integer division truncates remainder 7 / 5 evaluates to 1 (isn’t it interesting?) –Modulus operator returns the remainder 7 % 5 evaluates to 2 Operator precedence –Some arithmetic operators act before others (i.e., multiplication before addition) Be sure to use parenthesis when needed –Example: Find the average of three variables a, b and c Do not use: a + b + c / 3 Use: (a + b + c ) / 3

20. 20 Arithmetic Operators Arithmetic operators: Rules of operator precedence:

21. 21 Logical Op.: Decision Making

22. 22 What does a logical exp. evaluate? It evaluates a boolean value, i.e., true/false Certainly, a boolean variable can be automatically converted to other data types An interesting example bool c; char a = ‘Z’; c = (a = = 90); Question: what will be the value of c?

23. 23 “Hello, World!” std::cout –Standard output stream object –“Connected” to the screen –std:: specifies the "namespace" which cout belongs to std:: can be removed through the use of using statements << –Stream insertion operator –Value to the right of the operator (right operand) inserted into output stream (which is connected to the screen) –std::cout << “Hello, World!\n”; \ –Escape character –Indicates that a “special” character is to be output

24. 24 1. Load 2. main 2.1 Print "Welcome" 2.2 Print "to C++!" 2.3 newline 2.4 exit ( return 0 ) Program Output Welcome to C++! 1// Fig. 1.4: fig01_04.cpp 2// Printing a line with multiple statements 3#include 4 5int main() 6{6{ 7 std::cout << "Welcome "; 8 std::cout << "to C++!\n"; 9 10 return 0; // indicate that program ended successfully 11} Unless new line '\n' is specified, the text continues on the same line.

25. 25 Wanna get an input? >> (stream extraction operator) –When used with std::cin, waits for the user to input a value and stores the value in the variable to the right of the operator –The user types a value, then presses the Enter (Return) key to send the data to the computer –Example: int myVariable; std::cin >> myVariable; Waits for user input, then stores input in myVariable

26. 26 1. Load 2. main 2.1 Initialize variables integer1, integer2, and sum 2.2 Print "Enter first integer" 2.2.1 Get input 2.3 Print "Enter second integer" 2.3.1 Get input 2.4 Add variables and put result into sum 2.5 Print "Sum is" 2.5.1 Output sum 2.6 exit ( return 0 ) Program Output 1// Fig. 1.6: fig01_06.cpp 2// Addition program 3#include 4 5int main() 6{6{ 7 int integer1, integer2, sum; // declaration 8 9 std::cout << "Enter first integer\n"; // prompt 10 std::cin >> integer1; // read an integer 11 std::cout << "Enter second integer\n"; // prompt 12 std::cin >> integer2; // read an integer 13 sum = integer1 + integer2; // assignment of sum 14 std::cout << "Sum is " << sum << std::endl; // print sum 15 16 return 0; // indicate that program ended successfully 17} Enter first integer 45 Enter second integer 72 Sum is 117 Notice how std::cin is used to get user input. Variables can be output using std::cout << variableName. std::endl flushes the buffer and prints a newline.

27. 27 Save your typing … using statements –Eliminate the need to use the std:: prefix –Allow us to write cout instead of std::cout –To use the following functions without the std:: prefix, write the following at the top of the program using std::cout; using std::cin; using std::endl;

28. 28 1. Load 2. main 2.1 Initialize num1 and num2 2.1.1 Input data 2.2 if statements 1// Fig. 1.14: fig01_14.cpp 2// Using if statements, relational 3// operators, and equality operators 4#include 5 6using std::cout; // program uses cout 7using std::cin; // program uses cin 8using std::endl; // program uses endl 9 10int main() 11{ 12 int num1, num2; 13 14 cout << "Enter two integers, and I will tell you\n" 15 << "the relationships they satisfy: "; 16 cin >> num1 >> num2; // read two integers 17 18 if ( num1 == num2 ) 19 cout << num1 << " is equal to " << num2 << endl; 20 21 if ( num1 != num2 ) 22 cout << num1 << " is not equal to " << num2 << endl; 23 24 if ( num1 < num2 ) 25 cout << num1 << " is less than " << num2 << endl; 26 27 if ( num1 > num2 ) 28 cout << num1 << " is greater than " << num2 << endl; 29 30 if ( num1 <= num2 ) 31 cout << num1 << " is less than or equal to " 32 << num2 << endl; 33 The if statements test the truth of the condition. If it is true, body of if statement is executed. If not, body is skipped. To include multiple statements in a body, delineate them with braces {}. Enter two integers, and I will tell you the relationships they satisfy: 3 7 3 is not equal to 7 3 is less than 7 3 is less than or equal to 7 Notice the using statements.

29. 29 2.3 exit ( return 0 ) Program Output 34 if ( num1 >= num2 ) 35 cout << num1 << " is greater than or equal to " 36 << num2 << endl; 37 38 return 0; // indicate that program ended successfully 39} Enter two integers, and I will tell you the relationships they satisfy: 3 7 3 is not equal to 7 3 is less than 7 3 is less than or equal to 7 Enter two integers, and I will tell you the relationships they satisfy: 22 12 22 is not equal to 12 22 is greater than 12 22 is greater than or equal to 12 Enter two integers, and I will tell you the relationships they satisfy: 7 7 7 is equal to 7 7 is less than or equal to 7 7 is greater than or equal to 7

30. 30 Summary What we have learnt: –Basic C++ environment –Basic data types –Variables and addressing –Arithmetic/logical expressions –Basic I/O Questions remained: –How can we get a “line of characters” as the input? –Compare to a variable, how will such a line be stored in memory? –What can we do about that entire line of input?