1. Data Types, Primitive Types in C++, Variables – Declaration, Initialization, Scope Telerik Software Academy academy.telerik.com Learning and Development

2.  How computers work on data  Variables, example of using a variable in C++  What is a Data Type?  Identifiers in C++  Primitive Data Types in C++ and Using Them  Declaring Variables in C++  Variable Scope  Initializing Variables in C++  Default values 2

3. Variables, Using variables in C++, Identifiers

4.  Computers are machines that process data  Data is stored in the computer memory in variables  Variables have name, data type and value  Example of variable definition and assignment in C++ 4 int count = 5; Data type Variable name Variable value

5.  A data type:  Is a domain of values of similar characteristics  Defines the type of information stored in the computer memory (in a variable)  Examples:  Positive integers: 1, 2, 3, …  Alphabetical characters: a, b, c, …  Days of week: Monday, Tuesday, … 5

6.  A data type has:  Name (C++ keyword)  Size (how much memory is used)  Default value  Example:  Integer numbers in C++  Name: int  Size: 32 bits ( 4 bytes) – on Windows*  Default value: 0 * int is equal to the system “word”. E.g. x86 has 32-bit words. Windows always sets int to 32 bits Windows always sets int to 32 bitsWindows always sets int to 32 bits 6

7. Representing Integer, Floating-point and Symbolic values

8.  Integer types:  Represent whole numbers  May be signed or unsigned  Have range of values, depending on the size of memory used 8 NameDescriptionSize*Range* char Character or small integer. 1byte signed: -128 to 127 unsigned: 0 to 255 short int (short) Short Integer.2bytes signed: -32768 to 32767 unsigned: 0 to 65535 intInteger.4bytes signed: -2147483648 to 2147483647 unsigned: 0 to 4294967295 long int (long)Long integer.4bytes signed: -2147483648 to 2147483647 unsigned: 0 to 4294967295

9.  int – the most common integer type  char – symbolic & integer type  short int (or just short )  Smaller type than int  long int (or just long )  Same as int on most systems  long long int (or just long long )  Double the size of int on most systems 9

10.  C++ has no strict data type size on any type  Sizes determined by the system’s data types  i.e. int may be 32, 64 or even 16 bits  C++ standards before C++11 only guarantee:  Generally, using int is the best option sizeof(char)<=sizeof(short) sizeof(short)<=sizeof(int) sizeof(int)<=sizeof(long) sizeof(long) <=sizeof(long long) sizeof(char) == 1 //in bytes 10

11.  C++ works with two char types  One for storing 8-bit numbers  One for storing characters  Writing simply char invokes the character type  If we need to store numbers  Should write down " signed " or " unsigned "  Tell the compiler we need char for numbers  Note: don’t store numbers in char, unless you have a very good reason 11

12. Live Demo

13.  C++ has a Boolean type  bool – a value which is either true or false  Always takes up 1 byte  1 bit would be enough, but memory is addressed per bytes, not per bit  Takes true, false, or numeric values  Any non-zero numeric value is interpreted as true  Zero is interpreted as false 13

14. Live Demo

15.  Floating-Point numbers:  Represent real numbers (approximations)  2.3, 0.7, -Infinity, -1452342.2313, etc.  Range of values, depending on memory used  Accuracy, depending on memory used 15 NameDescriptionSize*Range* float Floating point number. 4bytes ±1.5 × 10 −45 to ±3.4 × 10 38 (~7 digits) double Double precision floating point number. 8bytes ±5.0 × 10 −324 to ±1.7 × 10 308 (~15 digits) long double Long double precision floating point number. 8bytes ±5.0 × 10 −324 to ±1.7 × 10 308 (~15 digits)

16.  float – fast, lower-precision  double – slower, higher precision  long double  High precision on some systems, not widely used  No guarantee on exact size (as with integers) sizeof(float)<=sizeof(double)<=sizeof(long double) 16

17. Live Demo

19.  When declaring a variable we:  Specify its type  Specify its name (called identifier)  May give it an initial value  The syntax is the following:  Example: 19 [= ]; [= ]; int height = 200;

20.  Variable names are called identifiers  All "words" in a language are identifiers  Data types  Operators  Functions  Identifiers in C++ are case-sensitive  THis != THIS != this  (the last being a reserved keyword) 20

21.  C++ identifiers  One or more letters, digits or underscores  Start with a letter or underscore  Avoid starting underscores & double underscores  May be compiler-reserved 21

22.  C++ identifiers  Can’t be a standard reserved keyword  Can’t be a name of operator representations  Can’t be a reserved compiler keyword  Some compilers reserve their own keywords  Bad C++ identifiers are detected compile-time  Don’t need to remember all rules  Compiler will warn you about errors 22

23.  Standard reserved identifiers in C++  Reserved identifiers for alternate operator representations (not always reserved) asm, auto, bool, break, case, catch, char, class, const, const_cast, continue, default, delete, do, double, dynamic_cast, else, enum, explicit, export, extern, false, float, for, friend, goto, if, inline, int, long, mutable, namespace, new, operator, private, protected, public, register, reinterpret_cast, return, short, signed, sizeof, static, static_cast, struct, switch, template, this, throw, true, try, typedef, typeid, typename, union, unsigned, using, virtual, void, volatile, wchar_t, while 23 and, and_eq, bitand, bitor, compl, not, not_eq, or, or_eq, xor, xor_eq

24.  Examples of correct identifiers:  Examples of incorrect identifiers: 24 int new;// new is a keyword int 2Pac;// Cannot begin with a digit int New = 2; // Here N is capital int _2Pac; // This identifiers begins with _ string greeting = "Hello"; int n = 100; // Undescriptive int numberOfClients = 100; // Descriptive // Overdescriptive identifier: int numberOfPrivateClientOfTheFirm = 100;

25. Live Demo

26.  Scope of a variable  Lines in code, where the identifier is valid  i.e. "where the variable is still alive"  Two kinds of scope in C++  Global (almost) – the variable is visible and usable by all functions in the program  Local – the variable is visible and usable only in the current block  i.e. in the inner-most { … } 26

27.  Making a local variable – declare it in a block  Making a global variable – declare outside any function or class int main() { int a = 5; //local variable return 0; } 27 #include #include int a = 5; //global variable int main() {a++; return 0; }

28. Ways to initialize, Default values

29.  C++ supports two ways of initializing  Through the assignment operator  Through calling the type constructor  Both ways are equivalent in the case of primitives int a = 5; 29 int a (5);

30.  What happens to uninitialized variables?  C++ allows operating on uninitialized variables  Actually variables get initialized sometimes  Even if not initialized, variables get values  Whatever was in that part of memory  Where the variable is placed int a; cout << a; 30

31.  Initialization depends on the variable scope  If the variable is global  Initialized to default type value  E.g. for integers 0  If the variable is local  Undefined in standard  Usually garbage values from memory  Whatever values in memory marked free 31

32. Live Demo

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