Chapter 4 Literals Variables and Constants 4 1

Chapter 4 Literals, Variables and Constants

4. 1 Literals Any numeric literal starting with 0 x specifies that the following is a hexadecimal value Any numeric literal starting with 0 is an octal value #Page 2

4. 1 Literals Character literals - single characters placed between apostrophes (‘) String literals - one or more characters placed between quotes ( “ ) Usually, treat single character as a character literal #Page 3

4. 2 Escape Sequences Escape sequence - exception to the rule that literals are interpreted exactly as they are written Escape sequences start with a backslash () followed by a single character Two types of escape sequences • Character • Numeric #Page 4

4. 2. 1 Character Escape Sequences Can be embedded in a string literal or be used as a character literal Escape Sequence Character Representation n Carriage return and line feed (new line) t Tab (eight characters wide) " Double quote ' Single quote \ Backslash Null character - a special character used, among other things, to give a character variable an initial value #Page 5

4. 2. 1 Character Escape Sequences cout << "This is on one linen This is on anothern"; cout << "t. He said, "Stop!""; // Output This is on one line This is on another He said, "Stop!" cout << "This is an apostrophe: "; cout << '''; // Output This is an apostrophe: ' #Page 6

4. 3 Variable Declarations Variable - a placeholder whose contents can change Everything must be declared before it is used #Page 7

4. 3 Variable Declarations A variable declaration has several purposes: • informs operating system how much internal memory (RAM) the variable will need • identifies the memory address to use for that variable • identifies the type of data to be stored in that physical memory location • indicates what operations (i. e. , +, -, /, etc. ) can be performed on the data contained within that variable #Page 8

4. 3 Variable Declarations Basic declaration syntax <data type> identifier; Data types discussed in the next section Identifier - the variable name int salary; // Notice the semicolon #Page 9

4. 3 Variable Declarations Multiple variables can be declared in the same statement int age, iq, shoe_size; Variables can be declared anywhere as long as they are declared before used #Page 10

4. 3. 1 Variable’s Initial Value When declared, its initial value is unknown Important to provide an initial value for all variables Initialization - process of giving a variable a value during its declaration - resulting in the variable always being in a known state int sum = 0; int Ralphs_age = RETIREMENT_AGE; int Randys_age = Ralphs_age - 26; #Page 11

4. 3. 1 Variable’s Initial Value Can initialize a variable to another variable’s value <data type> identifier 2 = identifier; int base_salary = 30000; int num_dependents, staff_salary = base_salary; #Page 12

4. 3. 1 Variable’s Initial Value Another form of initialization - uses parentheses instead of the assignment operator int base_salary( 30000 ); int num_dependents, staff_salary( base_salary ); #Page 13

4. 3. 2 Initialization Always know the state, or value, of all variables Variables should always be initialized Variables, even characters, are usually initialized to 0 #Page 14

4. 3. 3 Data Types A data type: • Specifies how much memory a variable will take up in memory • Indicates operations that can be performed on the variable Primitive data type - data type whose definition is built into the language #Page 15

4. 3. 3 Data Types C++ Data Type Description of Data Memory Allocated Range char Character 1 byte -128 to 127 int Integer OS Dependent float Floating point (decimal) 4 bytes 3. 4 E +/- 38 with 7 digits of accuracy double Double precision floating 8 bytes point 1. 7 E +/- 308 with 15 digits of accuracy bool Boolean data 1 byte true or false short (or short int) Smaller integer 2 bytes – 32, 768 to 32, 767 long Larger integer 4 bytes – 2, 147, 483, 648 to 2, 147, 483, 647 long double Larger double 8 bytes 1. 7 E +/- 308 with 15 digits of accuracy #Page 16

4. 3. 3 Data Types Boolean value - either true or false Size of an integer (int) - dependent upon the operating system • On a 16 -bit operation system such as Windows 3. x, an integer is 16 bits, or 2 bytes • On a 32 -bit operation system (Windows XP), an integer is 32 bits, or 4 bytes #Page 17

4. 3. 3 Data Types Size of an integer (int) - dependent upon the operating system (continued) • On a 64 -bit operation system - some versions of Windows Vista - an integer is 64 bits, or 8 bytes #Page 18

4. 3. 3 Data Types The amount of memory an integer requires determines the range of values In a 32 -bit operating system - since a bit can have one of two values - there will be 232 different possibilities #Page 19

4. 3. 3 Data Types Most significant bit is used as a sign bit • Zero meaning the number is positive • One means its negative • Therefore, left with 31 bits, or 231 different values #Page 20

4. 3. 3 Data Types Unsigned prefix for integral data types - the sign bit is used for data instead of the sign Integral data type - only holds whole numbers • • A char data type is an integral data type Under the hood a char holds an ASCII number representing a character Use smallest data type that will work with the data #Page 21

4. 3. 4 The sizeof Operator sizeof operator - determines number of bytes required for a specific data type // Part 1 cout << sizeof( char ) << 'n'; // Part 2 unsigned short age = 21; cout << sizeof( age ) << 'n'; // Output 1 2 #Page 22

4. 3. 5 Numeric Literal Suffixes Numeric literal suffix - special character used to specify the type of literal Numeric literal with an F suffix specifies a float, while L specifies a long value #Page 23

4. 3. 5 Numeric Literal Suffixes Either case will work for suffixes – but use capitals to avoid confusion between lower case l and a numeric 1 float money = 123. 45 F; // float avg = 95. 5 f; // long flag = 0 L; // // Last character is not long salary = 50000 l; Flt pt (4 bytes) numeric literals are treated as doubles (8 bytes) a one but a lowercase l #Page 24

4. 3. 6 Naming Rules Variable naming rules: • Only made up of letters, digits and underscores • Can’t start with a digit (must begin with a letter or underscore) • Can’t be a reserved word (if, else, while, etc. ) Variable names should be descriptive, aiding in code readability #Page 25

4. 4 ASCII Characters ASCII chart - associates characters with a number American Standard Code for Information Interchange (ASCII) #Page 26

4. 4 ASCII Characters Allow for the storage of characters in memory Some important ASCII values: • • 65 = ‘A’ 97 = ‘a’ 32 = ‘ ’ 48 = ‘ 0’ #Page 27

4. 4 ASCII Characters To display characters given an ASCII value use numeric escape sequences cout << "Hexadecimal ASCII character: " << "x 4 E" << endl; cout << "Octal ASCII character: " << "77" << endl; cout << "Hexadecimal number: " << 0 x 4 E << endl; cout << "Octal number: " << 077 << endl; //Output Hexadecimal ASCII character: N Octal ASCII character: ? Hexadecimal number: 78 Octal number: 63 #Page 28

4. 5 Constants - identifiers that have a value that will never change • Aid in code readability and maintainability • Should have a name that is descriptive of their purpose const int SPEED_LIMIT = 65; const int RETIREMENT_AGE = 67; const double PI = 3. 1416; #Page 29

4. 6 const versus #define To declare constants use the #define preprocessor directive #define SPEED_LIMIT 65 // Notice no = or semicolons #define RETIREMENT_AGE 67 #define PI 3. 14 Preprocessor searches through the code replacing the identifier with the value associated with it #Page 30

4. 6 const versus #define statements can cause compilation errors while looking syntactically correct #define PI = 3. 14; // Notice the = and ; int main() { int circumference = 0, radius = 5; circumference = 2 * PI * radius; return 0; } #Page 31

4. 6 const versus #define Although the statement looks correct, it causes a compilation error circumference = 2 * PI * radius; Error becomes clearer if we show what was created by the preprocessor circumference = 2 * = 3. 14; * radius; #Page 32

4. 6 const versus #define Use const versus #define because: • const uses a data type and participates in type checking • const has scope #Page 33

4. 7 Bringing It All Together Useful to picture how variables and constants might be placed in memory Examine the declarations below: short int age; char grade = 'A'; float gpa(0. 0); const float PI = 3. 14; #Page 34

4. 7 Bringing It All Together They may be placed in memory as shown below: ? ? A 0 0 3. 1 4 age grade gpa PI #Page 35

4. 8 Variable Declarations in Pseudocode Remember, pseudocode is a language independent representation of an algorithm Using data types has a tendency to make the solution to closely tied to C++ (or any other language) #Page 36

4. 8 Variable Declarations in Pseudocode Do not put variable declarations in pseudocode #includes are not specified in pseudocode and are considered necessary overhead to the algorithm #Page 37

4. 10 C – The Differences • C doesn’t have a Boolean data type (and no true or false) • Doesn’t allow for the use of parentheses to initialize variables or constants • In older versions of C, variables must be declared as the first statement in a block of code (after an opening curly brace)

4. 10 C – The Differences Current C standard allows a programmer to use const to create constants Legacy C programs written must use the #define to create constants