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Types

Types. Chapter 2. Objectives. Observe types provided by C++ Literals of these types Explain syntax rules for identifier names Study variables and constants What they are How they differ How to declare How to use Investigate internal representations

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Types

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  1. Types Chapter 2

  2. Objectives • Observe types provided by C++ • Literals of these types • Explain syntax rules for identifier names • Study variables and constants • What they are • How they differ • How to declare • How to use • Investigate internal representations • First look at class attribute variables C++ An Introduction to Computing, 3rd ed.

  3. Types and Declarations Fundamental Types • Integers (whole numbers, negatives) • int • Integer variations • short, long, unsigned • Reals (fractional numbers) • float, double, long double • Characters (letters, digits, symbols, punctuation) • char • Booleans (logical values, true and false) • bool C++ An Introduction to Computing, 3rd ed.

  4. Integer • Memory used for an int depends on word size used by the hardware • Usually 16, 32, or 64 bits used • 16 Bits (2 bytes) – shortint • Range -32768 … 32767 • 32bits (4 bytes) – longint (or long) • Range -2137483648 … 2137483647 (maybe 64) One bit used for the sign C++ An Introduction to Computing, 3rd ed.

  5. Integer • Integers can be specified as unsigned • Then the sign bit not needed • Gives larger positive range • unsigned short (16 bits) • Range 0 … 65535 • unsigned long (32 bits) • Range 0 … 4294967295 C++ An Introduction to Computing, 3rd ed.

  6. Integer Literals • Decimal integers • Sequence of digits without a decimal point • Octal integers • Sequence of digits beginning with a 0 • Base 8 • Hexadecimal integers • Sequence of digits beginning with an X • Base 16 C++ An Introduction to Computing, 3rd ed.

  7. Reals • float • Usually a 32-bit value (4 bytes) • double • A 64-bit value (8 bytes) • long double • A 96- or 128-bit value The programmer should choose which type based on degree of precision desired for the object C++ An Introduction to Computing, 3rd ed.

  8. Reals • Values are stored internally in scientific notation (base 2) • A sign for the number • Significant digits of the number • The power of 10 • Sign for the power C++ An Introduction to Computing, 3rd ed.

  9. Reals • Literal values (real Literals are treated as double) • A sequence of digits with leading sign, containing a decimal point • Scientific notation – any one of the following forms 0.12e11 1.2E10 12.0E9 12.e9 12E9 C++ An Introduction to Computing, 3rd ed.

  10. Characters • char type • Represents individual characters • See ASCII character set in Appendix A • Characters represented in memory by numeric values • Character literals • Characters enclosed in single quotes'X' '7' '>' 'e' C++ An Introduction to Computing, 3rd ed.

  11. Characters • Escape characters • A backslash \ combined with another character hold special meaning C++ An Introduction to Computing, 3rd ed.

  12. Strings • Need #include <string>; using namespace std; • A sequence of characters • Enclosed in double quotes"Hi Mom” • Can include escape characters"\nThe answer is " • Warning • "A" is a string literal • 'A' is a character literal C++ An Introduction to Computing, 3rd ed.

  13. Identifiers • Names given to software objects • Rules: • Must not be C++ keywords (see Appdx B)int, if, while, … • Must start with a letter (or the underscore _ ) • Followed by numerals, letters, underscore • Recommendation • Use meaningful identifiers • Go for longer names, rather than shorter C++ An Introduction to Computing, 3rd ed.

  14. Identifiers • C++ is case sensitive • firstName is not the same as firstname • Typical usage • Constants are all caps PI • Variables • Start with lower case • Capitalize first letter of successive wordsmonthlyElectricCharge C++ An Introduction to Computing, 3rd ed.

  15. Object Categories There are three kinds of objects: • Literals: • unnamed objects • having a value • (0, -3, 2.5, 2.998e8, ‘A’, “Hello\n”, ...) • Variables: • named objects • values can change during program execution • Constants: • named objects • values do not change during program execution C++ An Introduction to Computing, 3rd ed.

  16. Literals • int literals are whole numbers: -27, 0, 4, +4,012,0xA3B • double literals are real numbers, and can be: • fixed-point: -0.333, 0.5, 1.414, ... • floating-point: 2.998e8, 0.2998e9, ... • There are just twobool literals: false, true • char literals are single ASCII characters: ‘A’, ‘a’, ‘9’, ‘$’, ‘?’, ... • string literals are ASCII character sequences: “Hello”, “Goodbye”, “Goodbye\n”, ... C++ An Introduction to Computing, 3rd ed.

  17. Constants • Declaration of software objects that remain constant const double HOURLY_WAGE = 6.75; • Rules • const is a keyword • Specify type • Specify the name (caps recommended) • Must be initialized with value at declaration C++ An Introduction to Computing, 3rd ed.

  18. Constants • Reasons to use constants • Improve readability of the source code • Facilitate program modification • Good programming practice • Place all constant declarations at beginning of function where used • See some predefined constants in <climits> and <cfloat> libraries. (page 43) C++ An Introduction to Computing, 3rd ed.

  19. Variables • Give a name to a memory location • Compiler accesses specific memory location when program uses a given variable • Refer to objects in the program for which the value can change • Declarationtype variableName; // ortype variableName = initializer_expression; C++ An Introduction to Computing, 3rd ed.

  20. Variables • Variables Declaration • Can be either initialized or uninitialized... • If variable is uninitialized Contents must be considered "garbage value" • Examples: intage = 18; double GPA = 3.25, credits; char letterGrade = ‘A’; bool ok, done = false; C++ An Introduction to Computing, 3rd ed.

  21. int Representation • Integers are often represented in the twos-complement format, • High-order bit indicates the number’s sign: 210 = 00000000000000102 110 = 00000000000000012 010 = 00000000000000002 -110 = 11111111111111112 -210 = 11111111111111102 • We show 16 bits, but 32 or 64 are common. C++ An Introduction to Computing, 3rd ed.

  22. unsigned Objects • Some objects have values that are never negative, • C++ provides the unsigned type: 00000000000000002 = 010 00000000000000012 = 110 00000000000000102 = 210 ... 11111111111111102 = 6553410 11111111111111112 = 6553510 • No sign bit, numbers can be twice as big. C++ An Introduction to Computing, 3rd ed.

  23. int vs. unsigned • Using 32 bits, int values range from • -231 (-2147483648) to 231-1 (2147483647), • unsigned values range from • 0 to 232-1 (4294967295). • An int value “loses” one of its bits to the sign, • Maximum int value is about half of the maximum unsigned value. C++ An Introduction to Computing, 3rd ed.

  24. exponent (11 bits) sign (1 bit) mantissa (52 bits) double Objects • Real values are often represented in 64 bits • Use the IEEE floating point standard: C++ An Introduction to Computing, 3rd ed.

  25. double Objects • Overflow • Exponent is too large • Not enough bits to represent • Underflow • Number is so small • Not enough bits to represent negative exponent C++ An Introduction to Computing, 3rd ed.

  26. char and String Objects • Characters represented internally with binary codes • 8 bits – only 128 characters • Strings stored as a sequence of these binary codes C++ An Introduction to Computing, 3rd ed.

  27. char and String Objects • Unicode uses 16 bit codes • Possible to represent more than 65,000 characters • Can includespecialcharacters C++ An Introduction to Computing, 3rd ed.

  28. Booleans • Only two values • true and false • true stored as 1 • Anything non zero will be interpreted as true • false stored as 0 • Could be stored in a single bit • Usually stored in a word or byte C++ An Introduction to Computing, 3rd ed.

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