1 Objects Types, Variables, and Constants Chapter 3

Overview of C++ Statements 2 C++ Statements Declarations;Expressions; Other ObjectsOperations

Expressions In a C++ program, any finite sequence of ________ and __________ that combine to produce a value is called an expression. Examples from our temperature problem: __________ 1.8 * celsius 1.8 * celsius + 32 ________________________________________ 3 Even: 1.8; 32; "Hello"; 1 + 1; ;;;; We focus now on C++ objects and will look at operations later. Aside #1: expression Aside #1: expression ; is a statement.) Aside #2: expressions may be empty

Object Categories There are three kinds of objects: ___________: unnamed objects having a value ( 0, -3, 2.5, 2.998e8, 'A', "Hello\n",... ) named objects whose values can change during program execution __________: named objects whose values can change during program execution execution __________: named objects whose values cannot change during program execution 4 See Footnote on p.46 Have memory allocated to them

Literals – –_______ literals are integers: - 27, 0, 4, +4 – –_______ literals are real numbers, and can be: fixed-point: , 0.5, 1.414,... floating-point: 2.998e8, e9,... – –There are just two _____ literals: false, true – –_______ literals are single characters: 'A', 'a', '9', '$', '?',... – –_______ literals are sequences of characters: " Hello", "Goodbye", "Goodbye\n",... 5 or E Enclose in ' Enclose in " 5 basic types Not inter- changeable Some Variations: unsigned, long, short Variations: float, long double

Variable Declarations Examples: ___________________ cin >> celsius; _____________________________________________________ char letterGrade = 'A'; bool ok, done = false; Pattern: type name; type name = expression; 6 Allocates a memory location for values of this type and associates its address with name Declare only once Variables are used to store values, and can be either uninitialized or initialized. They must be _______________ before they are used.

Assignment Statements The value of a variable can be changed during execution by an assignment statement: Examples: _______________ ___________________________ letterGrade = 'B'; done = true; Pattern: name = expression; 7 Changes value in name's memory location to value of expression

Constant Declarations Constants are used to represent a value with a meaningful name, and must be initialized. They cannot be changed later. Examples: ____________________________________________ const char MIDDLE_INITIAL = 'A'; const string PROMPT = "Enter a number: "; Pattern: const type NAME = expression; 8 Allocates a memory location for values of this type, associates its address with NAME, puts value of expression in it, and locks it. Could use in Proj. 1.3

Identifiers The name of an object is called an _________ (because it identifies the object). C++ identifiers must begin with a letter (underscores are permitted, but discouraged) followed by zero or more letters, digits or underscores. Valid: age, r2d2, myGPA, MAX_SCORE Invalid: 123go, coffee-time, sam's, $name 9 May not be C++ keywords (See Appendix B)

Conventions We will use the following commonly-used convention to keep variable and constant objects distinct. Constant names: all uppercase, with multiple words separated by underscores (e.g., ___________) Variable names: all lowercase, with the first letter of each word after the first capitalized (e.g., ___________) 10 Use meaningful identifiers for readability! “camelback” notation

Objects char Objects Represented in memory by a ________ – –ASCII uses 8 bits (1 byte) to represent a character, allowing for 2 8 = 256 different characters – Now, 16, 24, or 32 bits. –Unicode's first version used 16 bits to represent a character, allowing for 2 16 = 65,536 different characters. Now, 16, 24, or 32 bits. Most commonly used code in C++ is ASCII: 'A' = ________________ 'a' = 97 = '0' = 48 = p.60 App. A Java chars can be treated as small integers; e.g,. char ch1 = 'A', ch2; int x = 2*ch1 + 1; ch2 = ch1 + 1; cout << x << ' ' << ch2 << '\n'; Output? ___________

Escape Characters C++ provides a number of _________ characters : '\n' newline character '\t' horizontal tab '\v' vertical tab '\f' form feed '\a' alert/bell '\\' backslash char '\'' apostrophe '\"' double quote '\ooo' char with octal code ooo '\xhhh' char with hex code hhh 12 See Appendix A

Objects int Objects Three forms: – –decimal (base-10) begin with 0 or a _________ digit or sign (-45, -2, 0, +21, 36, 65536,...) – –octal (base 8): begin with a ___ followed by octal digits (01, 02, 03, 04, 05, 06, 07, – –___________________________ _____________...) – –hexadecimal(base 16): begin with ____ followed by digits with a, b, c, d, e, f = 10, 11, 12, 13, 14, 15 (0x1, 0x2,..., 0x7, 0x8, 0x9, 0x, 0x, 0x, 0x, 0x, 0x, 0x, 0x,...) 13 See second item on Other Course Information class page

Objects unsigned Objects For integer objects whose values are never negative, C++ provides the ______________ type. They also may be expressed in decimal, octal, and hexadecimal forms. The major advantage of using unsigned instead of int when values being processed are known to be nonnegative is that larger values can be stored. 14

15 Using 32 bits, int values range from ( ) to ( ), whereas unsigned values range from 0 to ( ). An int value "loses" one of its bits to the sign, and so the maximum int value is about half of the maximum unsigned value. INT_MININT_MAX defines INT_MIN, INT_MAX, UINT_MAX, and other constants that specify ranges of C++ integers; does this for C++ real values. (See App. D) UINT_MAX Ranges of Integer Values

16 //-- Program to demonstrate the effects of overflow #include using namespace std; int main() { int number = 2; for (int i = 1; i <= 15; i = i + 1) { cout << number << '\n'; number = 10 * number; } Output: Strange Behavior of Integer Overflowoverflow Overflow: when a value gets out of range; for example, an integer exceeds INT_MAX = =

17 //-- Program to demonstrate the modular "wrap-around" effect of overflow #include using namespace std; int main() { int number = INT_MAX - 3; for (int i = 1; i <= 7; i = i + 1) { cout << number << '\n'; number = number + 1; } Output: Why this strange behavior? Check INT_MAX + 1, INT_MAX + 2,... INT_MAX INT_MIN Arithmetic is ___________________ INT_MIN... INT_MAX

Representation int Representation Integers are often represented internally in the ____________________ format, where the high- order (leftmost) bit indicates the number’s sign : 2 10 = = = = = Here we show 16 bits, but 32 or 64 are common. 18 Sec. 3.3

Twos-Complement To find twos-complement representation of a negative number: Represent its absolute value in binary: (_________________) Invert (complement) the bits: (_________________) Add 1 (_________________) Simpler: Flip all bits ________________________ 19 Try practice exercises — Week 3 of schedule

* : –6: Why Use Two's Complement? Because usual algorithms for +, * work! 111  carry bits

Objects double Objects Real values are often represented in 64 bits using the IEEE floating point standard: 5.75 = = sign (1 bit) mantissa (52 bits) exponent (11 bits) 21 float (single precision): bias = 127; exponent: 8 bits mantissa: 23 bits Try practice exercises on course schedule See Ch. 3, pp

22 //-- Effect of roundoff error #include #include using namespace std; int main() { for (double x = 0; x != 50.0; x = x + 0.1) for (double x = 0; x != 50.0; x = x + 0.1) { double y = x * sqrt(1 + sin(x)); double y = x * sqrt(1 + sin(x)); cout << x << " " << y << '\n'; cout << x << " " << y << '\n'; //if (x > 60) break; //if (x > 60) break; }} Execution: Problem:Binary representations of most real numbers do not terminate; e.g., 13.1 = … So they can't be stored exactly; error in this representation is called ____________________ Patriot missile failure See Other Course Information

23 /* temperature.cpp converts a Celsius temperature to Fahrenheit. John Doe Lab 1 Jan. 6, 2011 CPSC 104X Input: A Celsius temperature Output: Corresponding Fahrenheit temperature */ #include // cin, cout, > using namespace std; int main() { cout << "John Doe CPSC 104X -- Lab 1\n\n"; cout << "** Convert Celsius temps to Fahrenheit **\n"; cout << "Please enter a temperature in Celsius: "; double celsius; cin >> celsius; double fahrenheit = 1.8 * celsius + 32; cout << celsius << " degrees Celsius is " << fahrenheit << " degrees Fahrenheit.\n"; }