ECE 264 Object-Oriented Software Development Instructor: Dr. Michael Geiger Spring 2009 Lecture 2: Basic C++ Programs

Lecture outline Announcements / reminders  Web page is now online:  Additional lab notes/policies If you have a laptop, please bring it  24 machines in lab, but 32 / 25 students in W / F sections Remember: place a photo of yourself (photo.jpg) in your M:\drive (Quick) Pretest review Basic C++ programs 10/20/2015 ECE 264: Lecture 2 2

10/20/2015 ECE 264: Lecture 2 3 Pretest review Pretest intended to review the following  Control structures (if/else, switch, loops)  Basic data types  Array accesses  C output

Pretest review: if/else statements int x, y;. if (x < 5) { y = x + 1; } else { y = x – 2; } 1. At the end of the if/else statement above, if x = 4, y is equal to: a. 1b. 2 (1 person)c. 4d. 5 (55 correct) 2. Now, if x = 5, y is equal to: a. -2b. 3 (55 correct)c. 5d. 6 (1 person) 10/20/2015 ECE 264: Lecture 2 4

Pretest review: loops int x = 1; int i = 0; while (i <= 3) { x = x * 2; i++; } 3. Fill in the blank: The body of the while loop executes ______ times. a. 2b. 3 (7 people)c. 4 (49 correct)d. an infinite number of 4. The final value of x is: a. 2(3 people)b. 3 (1 person)c. 8 (12 people)d. 16 (40 correct) 5. Which of the following is a for loop that can replace the while loop and produce the same result for x? a. for (i = 1; i < 4; i++) (14 people) b. for (i = 0; i < 3; i++) (4 people) c. for (x = 0; x <= 3; x++) (3 people) d. for (i = 3; i >= 0; i--) (35 correct) 10/20/2015 ECE 264: Lecture 2 5

Pretest review: arrays, I/O int A[5] = {0, 7, 13, 12, 5}; for (i = 0; i < 5; i++) { printf(“A[%d] + 3 = %d\n”, i, A[i] + 3); } 6. In the first iteration, the program will display the following text on the screen: a. A[%d] + 3 = %d\n(1 person) b. A[i] + 3 = A[i] + 3(2 people) c. A[0] + 3 = 3 (53 correct) d. A[1] + 3 = The value of A[4] is: a. 4 (1 person)b. 5 (31 correct)c. 12 (19 people) d. non-existent (5 people) 10/20/2015 ECE 264: Lecture 2 6

Pretest review: switch statements switch (var) { case 0: case 1: x = x + var; break; case 2: x = x – var; case 3: x = x * var; break; default: x = var; } Assume x always equals 5 at the start of the switch statement. What is the value of x at the end of the statement if: 8. var = 1? a. 1(5 people)b. 4 (2 people)c. 5 (7 people)d. 6 (42 correct) 9. var = 2? a. 2(8 people)b. 3 (39 people) c. 6 (7 correct)d. 7 (1 person) 10. var = 5? a. 0 (1 person) b. 5 (51 people)c. 10 (2 people) d. 25 (1 person) 10/20/2015 ECE 264: Lecture 2 7

Basic C++ programs We’ll cover the following today  Basic structure of a C++ program  Constants and variables  Identifiers  C++ operators  Standard input and output 10/20/2015 ECE 264: Lecture 2 8

Example program #1 /* Simple C++ Program */ /* This program computes the */ /* distance between two points. */ #include // Required for cout, endl. #include // Required for sqrt() using namespace std; int main() { // Declare and initialize objects. double x1(1), y1(5), x2(4), y2(7), side1, side2, distance; // Compute sides of a right triangle. side1 = x2 - x1; side2 = y2 - y1; distance = sqrt(side1*side1 + side2*side2); // Print distance. cout << "The distance between the two points is " << distance << endl; // Exit program. return 0; } 10/20/2015 ECE 264: Lecture 2 9

Comments Comments help people read code, but are ignored by the compiler C++ (like C) has two types of comment  // Single line comments end at the end of a line  /* Delimited comments start and end as shown here and can span multiple lines. */ Good programming practice to  Start file with comment describing purpose  Comment functionality of each section of code 10/20/2015 ECE 264: Lecture 2 10

Preprocessor directives Provide instructions to the compiler that are performed before the program is compiled. Begin with a # Example:  #include The #include directive instructs the compiler to include statements from the header file iostream. 10/20/2015 ECE 264: Lecture 2 11

using Directive The using directive instructs the compiler to use files defined within a specific namespace  Namespaces allow us to declare different scopes Example:  using namespace std;  std is the name of the Standard C++ namespace  Including this line allows you to avoid specifying namespace for every identifier in your headers Otherwise, cout would have to be std::cout, etc. 10/20/2015 ECE 264: Lecture 2 12

Block of Code A block of code is defined by a set of curly braces {…}. Can contain comments and statements  Statements can end in semicolon (;) or be enclosed in braces (e.g. if ) Example: int main() { //Block defines body of main function double x1(1), x2(4), side1; side1 = x2 – x1; cout << side1 << endl; return 0; // main()returns int value of 0 } //end definition of main Every C++ program must contain exactly one function named main() C++ program solutions always begin execution in main() 10/20/2015 ECE 264: Lecture 2 13

Constants and Variables Constants and variables represent memory locations that we reference in our program solutions. Constants are objects storing specific data that can not be modified.  10 is an integer constant  4.5 is a floating point constant  "Side1" is a string constant  'a' is a character constant Variables are memory locations that store values that can be modified. double x1(1.0), x2(4.5), side1; side1 = x2-x1;  x1, x2 and side1 are examples of variables that can be modified. 10/20/2015 ECE 264: Lecture 2 14

Memory Snapshot 10/20/2015 ECE 264: Lecture 2 15 #include using namespace std; int main() { double x1(1.0), x2(4.5), side1; double x1 double x2 double side1 side1 = x2-x1; double x1 double x2 double side1 cout << “side 1 has length: “ side1; ? Output: side 1 has length: 3.5

10/20/2015 ECE 264: Lecture 2 16 Common C++ Data Types KeywordExample of a constant booltrue char'5' int25 double25.0 string"hello" // #include

C++ Identifiers Identifiers are used to name objects in C++. Rules for selecting valid identifiers:  Identifier must begin with a letter or underscore _  Identifiers consists of alphanumeric characters and underscore character only  An identifier can not be a reserved word  Only the first 31 characters of an identifier are used to distinguish it from other identifiers. C++ is case sensitive Good programming practice: choose descriptive identifiers 10/20/2015 ECE 264: Lecture 2 17

Declarations A declaration statement defines new identifiers and allocates memory Can assign initial value in declaration Syntax: [modifier] data_type identifier_list; Examples: double length(20.75), width(11.5), volume; int numberOfFeetInYard(3); const int MIN_SIZE = 0;  Text uses: identifier(initial_value) (C++ specific)  Could just as easily use: identifier = initial_value Good programming practices  Grouping declarations together for similarly used variables or using 1 per line allows you to comment them meaningfully  Separate declarations from rest of program using whitespace 10/20/2015 ECE 264: Lecture 2 18

Symbolic Constants A symbolic constant is defined in a declaration statement using the modifier const. A symbolic constant allocates memory for an object that can not be modified during program execution  Attempt to modify constant  syntax error A symbolic constant must be initialized in the declaration statement 10/20/2015 ECE 264: Lecture 2 19

Assignment Operator The assignment operator (=) is used in C++ to assign a value to a memory location. The assignment statement: x1 = 1.0;  assigns the value 1.0 to the variable x1.  Thus, the value 1.0 is stored in the memory location associated with the identifier x1. 10/20/2015 ECE 264: Lecture 2 20

10/20/2015 ECE 264: Lecture Example 1 - initialization double sum = 0; sum 4 Example 2 int x; x=5; x Assignment Operators - Examples 0 5 a 4 Example 3 char ch; ch = 'a'; ch

10/20/2015 ECE 264: Lecture 2 22 Assignment Statements - continued Example 4 int x, y, z; x=y=0; z=2; x y z How is the memory map affected by the following statement? y = z; 0 0 2

10/20/2015 ECE 264: Lecture 2 23 Arithmetic Operators Addition+ Subtraction- Multiplication* Division/ Modulus%  Modulus returns remainder of division between two integers  Example 5%2 returns a value of 1

10/20/2015 ECE 264: Lecture 2 24 Integer Division Division between two integers results in an integer. The result is truncated, not rounded Example: The expression 5/3 evaluates to 1 The expression 3/6 evaluates to 0

10/20/2015 ECE 264: Lecture 2 25 Priority of Operators 1.ParenthesesInner most first 2.Unary operatorsRight to left (+ -) 3.Binary operatorsLeft to right (* / %) 4.Binary operatorsLeft to right (+ -)

Increment/decrement operators Increment Operator ++ post incrementx++; pre increment++x; Decrement Operator - - post decrementx- -; pre decrement- -x; For examples assume k=5 prior to executing the statement. m= ++k;both m and k become 6 n = k- -;n becomes 5 and k becomes 4 10/20/2015 ECE 264: Lecture 2 26

10/20/2015 ECE 264: Lecture 2 27 Abbreviated Assignment Operators operatorexampleequivalent statement +=x+=2; x=x+2; -=x-=2;x=x-2; *=x*=y;x=x*y; /=x/=y;x=x/y; %=x%=y;x=x%y;

10/20/2015 Engineering Problem Solving with C++, Etter,Ingber Second Edition 28

Input/output streams C++ has three standard input/output streams  cin is the standard input (e.g., keyboard)  cout is the standard output  cerr is the standard error Standard input  Use the stream input operator >> to direct keyboard input to variables  General Form: cin >> identifier >> identifier;  Input value must be compatible with identifier type 10/20/2015 ECE 264: Lecture 2 29

Input/output streams (cont.) Standard output  Use the stream output operator << to direct data to cout  General Form: cout << expression << expression;  Note: An expression is a C++ constant, identifier, formula, or function call.  endl can be used to place an output character in the buffer and flush the buffer 10/20/2015 ECE 264: Lecture 2 30

10/20/2015 Engineering Problem Solving with C++, Etter,Ingber Second Edition 31 output 1,2 4.5 cm _ //Example1: Determine the output #include using namespace std; int main() { int i, j; double x; string units = " cm"; cin >> i >> j; cin >> x; cout << "output \n"; cout << i << ',' << j << endl << x << units << endl; return 0; } //Input stream:

10/20/2015 Engineering Problem Solving with C++, Etter,Ingber Second Edition 32 //Example 2: Determine the output #include using namespace std; int main() { int i, j; double x, y; cin >> i >> j >> x >> y; cout << "First output " << endl; cout << i << ',' << j << ',' << x << ',' << y << endl; cin >> x >> y >> i >> j; cout << "Second output" << endl; cout << i << ',' << j << ',' << x << ',' << y << endl; return 0; } //Input stream is: First output 1,2,3.4,5 Second output 3,2,2,3 _

10/20/2015 Engineering Problem Solving with C++, Etter,Ingber Second Edition 33 Characters and input >> discards leading whitespace get() method used to input whitespace characters Example: int x; char ch; cin >> x >> ch; cin >> x; cin.get(ch); xch xch Input stream: 45 c 39 b 45‘c’ 39‘\n ’

Final notes Next time Functions in C++--pass by value, reference Potentially cover pointers as well Acknowledgements: this lecture borrows heavily from lecture slides provided with the following texts: Etter & Ingber, Engineering Problem Solving with C++, 2 nd ed. Deitel & Deitel, C++ How to Program, 6 th ed. 10/20/2015 ECE 264: Lecture 2 34