Chapter 2

1. Chapter 2 Data types, declarations, and displays

2. Computer data processing • Data processing: the process of using a computer to convert raw data (unprocessed or unorganized) data into information (processed data).

3. Data types • Numeric (dimensionless) • integer type: 450, 25000, -99, etc. • floating point type • Ordinary notation: 3.1415, 6.99, -12000., etc. • Exponential notation: for very large or very small values such as 6.25e9, -3.5e-10, etc. • Character type: a single character enclosed in a pair of single quote such as ‘a’, ‘Z’, ‘$’, etc. In C/C++ system, a character is internally treated/represented as an small integer, e.g., ‘a’ is actually 97 ‘A’ is 65.

4. Data types continued • Character type: although C/C++ treats a single character as an integer, each character is encoded using a group of eight bits following a coding standard known as ASCII (American Standard for Information Interchange) of ANSI (American National Standard Institute). For example, when you hit ‘a’ key, a group of eight bits 01100001 goes into the memory (see p38). • Boolean or logical type: recent C/C++ standard supports Boolean type. A Boolean data type allows only two different values of either true or false. Again, Boolean values are treated by C/C++ as two small integer values --- 1 for true and 0 for false.

5. Data types continued • Character type: there are a small set of characters known as escape sequence (or escape characters) including ‘\n’ (a new line character), ‘\t’ (next tab stop character), etc. (see Tab 2-3 on p39). Although there are two characters enclosed in a pair of single quotes, the two characters are treated as a single character or more precisely, a small integer, ‘\n’ is 10 and ‘\t’ is 9. Note that escape character such as ‘\n’ and ‘\t’ play important role in output operation. • String type: a series or a list of characters enclosed in a pair of double quotes such as “William Paterson Univ”, “Net Income”, etc.

6. How is main memory (RAM) organized and accessed • RAM is byte-addressable (each byte has a unique address) with a one-dimension or linear memory space, i.e., one byte after another. • How many bytes are needed to store an integer, a floating point number, a character, or a string?

7. Size of storage or memory needed to store a piece of data • Integer type • short: 2 types • int: 2 types • long: 4 types • Floating • float: 4 bytes • double: 8 bytes • long double: 10 bytes It is noted that the larger the size of storage, the wider the range and more precise can a value be stored. Also noted is the fact that the sizes are dependent on the compiler! The numbers quoted are for Turbo C/C++ compiler.

8. Arithmetic operators • + (addition), - (subtraction), * (multiplication), / (division), % (modulo division). Note that except for modulo division operator which operate on integers, all other four operator operate on either integer or floating point types of data. • Property of an operator • arity: number of operands operated upon by the operator. • priority or precedence: the order of operations when two or more operators appear in a statement or expression. • associativity: either left-to-right or right-to-left.

9. Arithmetic operators continued • All operators are binary operators (with arity = 2) since each operates on two operand such as 4 * 5, 8 – 6, etc. • the – operator can be a unary negation operator (one operand) as in –25, where – simply mean negative 25. • The associativity is left-to-right meaning 5 - 3 is actually 5 minus 3, not 3 minus 5. • *, /, and % are of the same priority and are higher than + and -, meaning 2 + 3 * 5 is equal to 17 instead of 25! Note that precedence can be overridden with parentheses.

10. Integer division • 5 / 3 yields 1 (quotient) • 99 / 100 yields 0 (quotient) • 5 % 3 yields 2 (remainder) • 99 % 100 yields 99 (remainder) • etc.

11. Mixed mode operation and data type promotion • In an arithmetic expression, there are two or more operands of different types (a mix of integer and floating point types) Example: 2 + 3.5(2 will be promoted to double type before computation will take place) 4.85 – 3.1415926L(4.85 will be promoted to long double type before computation will proceed) etc.

12. Output using cout • Data flows like a stream (one character after another) to or out of a C++ program. • cout is an ostream (output stream) object (it is helpful to view it as an output stream); it is used together with the insertion operator <<, which inserts whatever follows it to the output stream. Example: cout << “Hello World!” << endl; cout << (2 + 3) << endl; cout << “The first alphabet is “ << ‘a’ << endl; cout << “The total of 6 and 15 is “ << (6 + 15); etc…

13. The insertion operator << is “overloaded” • Notice the insertion operation recognizes and inserts (or operates on) different types data item onto the output stream (which flows from the program to a printer or monitor); the insertion operator is said to be overloaded.

14. Formatted output • For simple formatting, one can use escape sequence such as ‘\n’ (newline) and/or ‘\t’ (next tap stop). • For more sophisticated formatting, one must use stream manipulators which are defined by the C/C++ system.

15. Commonly used stream manipulators • setw( n ): set field width to n • setprecision( n ): set floating point precisin to n places • setiosflag( flags ): set the format flags • dec: display a value in decimal notation • hex: display a value in hexadecimal notation • oct: display a value in octal notation

16. Example: Version 1; printout not properly aligned #include <iostream.h> { cout << 6 << endl << 18 << endl << 124 << endl << “---\n” << (6 + 18 + 124) << endl; return 0; }

17. Example: Version 2; printout of integers is now properly aligned with setw(n) #include <iostream.h> #include <iomanip.h> { cout << setw(3) << 6 << endl << setw(3) << 18 << endl setw(3) << 124 << endl << “---\n” << (6 + 18 + 124) << endl; return 0; } // Note: setw(n) is non-persistent; integer right-justified in the specified print field

18. Formatting floating point numbers … cout << ‘|’ << setw(10) << setiosflags( ios::fixed ) << setprecision(3) << 25.67 << ‘|’; … The above output instruction displays: | 25.670| Note that the setprecision manipulator defaults to 6 decimal places.

19. More examples on the effect of format manipulators are shown in table 2-8, page 52

20. Format flags for use with setiosflags( ) on page53 • ios::showpoint • ios::showpos • ios::fixed • ios::scientific • ios::dec • ios::oct • ios::left • ios::right

21. A program that illustrates output conversions #include <iostream.h> #include <iomanip.h> int main() { cout << “The decimal value of 15 is “ << 15 << endl << “The octal value of 15 is “ << setiosflags(ios::oct) << 15 << endl << “The hexadecimal value of 15 is “ << setiosflags(ios::hex) << 15 << endl; return 0; }

22. A simpler version #include <iostream.h> #include <iomanip.h> int main() { cout << “The decimal value of 15 is “ << 15 << endl << “The octal value of 15 is “ << oct << 15 << endl << “The hexadecimal value of 15 is “ << hex << 15 << endl; return 0; }

23. Variable and its declaration • A variable is a name (identifier) that identifies a memory location in which a value (a piece of data) can be stored. • It is helpful to visualize a memory location as a box, and the size of the box depends on data type, e.g., 1 byte for char type, 2 bytes for int type, and 8 bytes for double type. • The variable name is associated with the actual physical address of the location in RAM. • the variable name can be arbitrarily chosen by the programmer subjected to the following restrictions: (next slide)

24. Variable name • It is case-sensitive! • It must not be a keyword! • It must begin with a letter or an underscore • It cannot contain more than 31 characters • It must not have embedded space. • Upper and lower case alphabets, digits (0 through 9) and some special characters such as underscore _ are allowed. • It is desirable to choose meaningful names, e.g., a variable name tax would presumably be used to store tax value(s).

25. Declaration of variables • A variable must be declared before it can be used. It is declared according to the following format: data-type variable-name; where data-type is a reserved word and variable is an identifier chosen by the programmer. Valid data types include char, int, double, etc.

26. Data types • Integer: short, int, long • Floating-point: float, double, long double • Character: char • Boolean or logic: bool Example: char gender; int age; double interestRate, principal;

27. The assignment operator = • Remember that a variable is a named memory location in which a value can be stored. So, once a variable is declared, a value can be assigned to or stored in it through the use of the assignment operator. The format is as follows: variable = value; The entire line above is known as an assignment statement

28. Example: compute the average of three test scores #include <iostream.h> int main( ) { float grade1, grade2, total, average; grade1 = 85.5; grade2 = 97.0; total = grade1 + grade2; average = total / 2.0; cout << “The average grade is “ << average << endl; return 0; }

29. Example: character variable #include <iostream.h> int main() { char ch; ch = ‘a’; cout << “The character stored in ch is << ch << endl; ch = ‘m’; cout << “The character now stored in ch is “ << ch; return 0; }

30. Reference variable: additional name or alias of the same variable • Once a variable has been defined, it may be given additional names. It is accomplished by using a reference declaration: data-type &new-name = existing-name; Example: float total; float &sum = total

31. Program involving reference variable #include <iostream.h> int main() { float total = 20.5; // declare and initialize float &sum = total; cout << “Sum = “ << sum << endl; sum = 18.6; cout << “Total = “ << total << endl; return 0; }