Chapter 4 Literals, Variables and Constants

#Page2 4.1 Literals Any numeric literal starting with 0x specifies that the following is a hexadecimal value Any numeric literal starting with 0 is an octal value

#Page3 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

#Page4 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 Character Escape Sequences Can be embedded in a string literal or be used as a character literal Null character - a special character used, among other things, to give a character variable an initial value Escape Sequence Character Representation \n Carriage return and line feed (new line) \t Tab (eight characters wide) \"Double quote \'Single quote \\Backslash \0Null character

#Page Character Escape Sequences cout << "This is on one line\n This is on another\n"; cout << "\tHe 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: '

#Page7 4.3 Variable Declarations Variable - a placeholder whose contents can change Everything must be declared before it is used

#Page8 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

#Page9 4.3 Variable Declarations Basic declaration syntax identifier; Data types discussed in the next section Identifier - the variable name int salary; // Notice the semicolon

#Page 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 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 Variable’s Initial Value Can initialize a variable to another variable’s value identifier2 = identifier; int base_salary = 30000; int num_dependents, staff_salary = base_salary;

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

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

#Page 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 Data Types C++ Data Type Description of Data Memory Allocated Range charCharacter1 byte-128 to 127 intIntegerOS Dependent floatFloating point (decimal)4 bytes 3.4E +/- 38 with 7 digits of accuracy double Double precision floating point 8 bytes 1.7E +/- 308 with 15 digits of accuracy boolBoolean data1 bytetrue or false short (or short int) Smaller integer2 bytes–32,768 to 32,767 longLarger integer4 bytes –2,147,483,648 to 2,147,483,647 long doubleLarger double8 bytes 1.7E +/- 308 with 15 digits of accuracy

#Page 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 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 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 2 32 different possibilities

#Page 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 2 31 different values

#Page 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 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 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 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 = F;// Flt pt (4 bytes) numeric float avg = 95.5f; // literals are treated as long flag = 0L; // doubles (8 bytes) // Last character is not a one but a lowercase l long salary = 50000l;

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

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

#Page ASCII Characters To display characters given an ASCII value use numeric escape sequences cout << "Hexadecimal ASCII character: " << "\x4E" << endl; cout << "Octal ASCII character: " << "\77" << endl; cout << "Hexadecimal number: " << 0x4E << endl; cout << "Octal number: " << 077 << endl; //Output Hexadecimal ASCII character: N Octal ASCII character: ? Hexadecimal number: 78 Octal number: 63

#Page Constants 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 = ;

#Page 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 const versus #define #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 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 const versus #define Use const versus #define because: const uses a data type and participates in type checking const has scope

#Page 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 Bringing It All Together They may be placed in memory as shown below: ??A age grade gpa PI

#Page36 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) 4.8 Variable Declarations in Pseudocode

#Page Variable Declarations in Pseudocode Do not put variable declarations in pseudocode #include s are not specified in pseudocode and are considered necessary overhead to the algorithm

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