Documentation Need to have documentation in all programs Documentation header Regular comments inside programs Follow department standard Copy-and-paste shell command in Putty Highlight the part to copy Right-click to paste

Review Q. What does #include do? Q. What is namespace std? Q. How many main( ) function(s)? Q. What does a preprocessor do? cout cout<<“Hello “<< “World!”<<endl; “\n” and endl Refer to example in PPT2

Variable Named memory location Used to hold data Name Type Capacity Different type holds different kinds of data Capacity How large is this location? Determined by type Duration Gets recycled after lifetime is over pp67-68

To define a variable Specify type and name int num; // reserve a location of four bytes in RAM // used for storing an integer // reference the location using name num Define several variables of same type in an instruction int rate, hour, pay; //reserve three locations with four bytes each pp67

Rules for choosing variable names Use numbers, letters, underscore Cannot start with number Cannot be keywords Make it meaningful C++ is case sensitive! Hour and hour are two different variables! pp68

Valid and Invalid variable names IDENTIFIER VALID? REASON IF INVALID totalSales total_Sales total.Sales 4thQtrSales totalSale$

Valid and Invalid variable names IDENTIFIER VALID? REASON IF INVALID totalSales Yes total_Sales total.Sales No Cannot contain . 4thQtrSales Cannot begin with digit totalSale$ Cannot contain $

Variable Type: Integer positive and negative whole numbers, e.g. 5, -52, 343222 short, int, long represented internally in binary 16 is represented as 00010000 To define: int number; pp63

Variable Type: Floating point number Real number (integral and fractional part) 2.5, 3.66666666, -.000034, 5.0 float, double, long double Stored internally as mantissa and exponent (base 2) 16.0 is represented as mantissa 1.0 and exponent 4 pp64

Variable Type: Floating point number To define: float amount; double hour, rate; pp64

Variable Type: Boolean Logical variable Named for George Boole Values: true and false To define: bool flag; pp65

Variable Type: Character represent individual character values E.g. ’A’ ’a’ ’2’ ’*’ ’”’ ’ ’ stored in 1 byte of memory special characters: escape sequences ’\n’ ’\b’ ’\r’ ’\t’ ‘\’’ To define: char letter; pp65

string type A sequence of characters Can contain zero or more character “” empty string “A” string with one char “Hello” string with five characters pp66

string type Be careful with single and double quotes (“ versus ")when using word processor Not a primitive type (size varies) A string can have arbitrary number of characters pp66

To define a string Same syntax string course_name; //reserve 2 or 4 bytes to store the //address of the string //store the string dynamically in //another place string course_name; pp66

In summary For whole numbers For floating point numbers short (2 bytes) int (4 bytes) long (4 or 8 bytes) For floating point numbers float (4 bytes) double (8 bytes) For single character char (1 byte) For Boolean (true/false) values bool (1 bit) For string string (varies)

More examples float x, y; int num1, num2; float salary; string flower_name;

Assignment operator = Two-step action Evaluate the value of right hand side Assign the value to left hand side int num; num = 5; num = num + 1; num = num * 2; num = num * num; pp71

Left hand side must be a variable 12 = item; // ERROR! Left hand side does not reference a location a + 5 = a; //Same error

Variable initiation Combine variable declaration and initial assignment into a single instruction int num = 5; //declare an integer variable num //assign 5 to num Can also write them separately int num; num = 5;

Variable declaration without initial values An uninitialized variable has a random value, i.e. we do not know what value is stored int num; char letter; float rate;

Literal vs. Variable A literal is a value that is written into a program’s code. "hello, there" (string literal) 12 (integer literal) ‘C’ (character literal) 3.5 (floating point number literal) Value of a literal cannot be changed. 3 is always 3. Value of a variable can be changed. pp63, 66

20 is an integer literal

This is a string literal

This is also a string literal

Output a variable The current value of the variable will be printed Don’t enclose a variable name in double quotes int num= 5; num = num * num; cout << “The value of num is “ << num << endl;

More examples char letter = ‘c’;//declare letter, assign ‘c’ to letter //don’t forget single quote Q. What about the following? char letter = c; //c is considered as a variable //Error! may or may not compile

More examples bool flag = true; // true is a keyword string name = "John"; //use double quote string name = John; // Error! John is treated as a variable name

Define before use

What is the output? int a=5, b=7, c=10; a = a + 3; b = a + c; cout << a << “ “ << b << “ “ << c << endl; Every object (string, variable, or manipulator) needs a separate << in a cout instruction. //Error! cout << a << “ “ << b << “ “ c << endl; => 8 18 10

Characters and strings A character is stored as its ASCII value (Appendix B) ‘A’ 65 ‘B’ 66 ‘y’ 121 ‘$’ 36 A string is stored as a sequence of characters “John” Always has the NULL character (‘\0’) at the end 74 111 104 110 \0

‘A’ and “A” Q. Are they the same? ‘A’ is a single character, stored in 1 byte of memory “A” is a string of length one, stored as 2 bytes of memory 65 65 \0

Summary Variable basics Literals How to declare and initialize Various types Assignment operator Difference between characters and strings Output variable values using cout Literals

Review Section 2.3 Variable types and declarations http://www.cppforschool.com/tutorial/variable-memory-concept.html