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Programming. Declarations. General form of a C++ program. // Program description #include directives int main(){ constant declarations variable declarations

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programming

Programming

Declarations

general form of a c program
General form of a C++ program

// Program description

#include directives

int main(){

constant declarations

variable declarations

executable statements

return 0;

}

c data type
C++ Data Type

A type defines a set of values and a set of operations that can be applied on those values. The set of values for each type is known as the domain for the type.

C++ contains 5 standard types:

slide4
void

The void type has no values and no operations. In other words, both the set of values and the set of operations are empty. Although this might seem unusual, we will see later that it is a very useful data type.

integer
Integer

An integer type is a number without a fractional part. It is also known as an integral number. C++ supports three different sizes of the integer data type: shortint, int and longint.

sizeof(short int)<= sizeof(int)<= sizeof(long int)

Short int

int

long int

integer1
Integer

The type also defines the size of the field in which data can be stored. In C++, even though the size is machine dependent, most PCs use the integer sizes shown below.

floating point
Floating Point

A floating-point type is a number with a fractional part, such as 43.32. The C++ language supports three different sizes of floating-point: float, double and long double.

sizeof(float)<= sizeof(double)<= sizeof(longdouble)

float

double

long double

floating point1
Floating Point

Although the physical size of floating-point types is machine dependent, many computers support the sizes shown below.

declarations
Declarations
  • Constants and variables must be declared before they can be used.
  • A constant declaration specifies the type, the name and the value of the constant.
  • A variable declaration specifies the type, the name and possibly the initial value of the variable.
  • When you declare a constant or a variable, the compiler:
    • Reserves a memory location in which to store the value of the constant or variable.
    • Associates the name of the constant or variable with the memory location. (You will use this name for referring to the constant or variable.)
  • For more on declarations, see www.courseware.ust.hk and choose English--> C++ --> Declarations.
constant declarations
Constant declarations
  • Constants are used to store values that never change during the program execution.
  • Using constants makes programs more readable and maintainable.

Syntax:

const <type> <identifier> = <expression>;

Examples:

const double US2HK = 7.8;

//Exchange rate of US$ to HK$

const double HK2TW = 3.98;

//Exchange rate of HK$ to TW$

const double US2TW = US2HK * HK2TW;

//Exchange rate of US$ to TW$

variable declarations
Variable declarations
  • Variables are used to store values that can be changed during the program execution.
  • A variable is best thought of as a container for a value.

3445 y -3.14

Syntax:

< type > < identifier >;

< type > < identifier > = < expression >;

Examples:

intsum;

int total = 3445;

char answer = 'y';

double temperature = -3.14;

variable declarations1
Variable declarations
  • A variable has a type and it can contain only values of that type. For example, a variable of the type int can only hold integer values.
  • Variables are not automatically initialized. For example, after declaration

intsum;

the value of the variable sumcan be anything (garbage).

  • Thus, it is good practice to initialize variables when they are declared.
  • Once a value has been placed in a variable it stays there until the program deliberately alters it.
character data
Character data
  • A variable or a constant of char type can hold an ASCII character (see Appendix A of the textbook).
  • When initializing a constant or a variable of char type, or when changing the value of a variable of char type, the value is enclosed in single quotation marks.

Examples:

const char star = '*';

char letter, one = '1';

computers are easy
Computers are Easy!
  • "Using a computer is just like riding a bike, except you don't have to wear the tight shorts and funny helmet. A water bottle is also a bad idea. Just about everyone agrees that computing is very simple, or will be in only a few more days.
      • David Lubar, 1995
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