Programming Declarations

COMP102 Prog. Fundamentals I: Declarations/ Slide 2 General form of a C++ program // Program description #include directives int main(){ constant declarations variable declarations executable statements return 0; }

COMP102 Prog. Fundamentals I: Declarations/ Slide 3 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:

COMP102 Prog. Fundamentals I: Declarations/ Slide 4 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.

COMP102 Prog. Fundamentals I: Declarations/ Slide 5 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: short int, int and long int. sizeof(short int)<= sizeof(int)<= sizeof(long int) Short int int long int

COMP102 Prog. Fundamentals I: Declarations/ Slide 6 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. TypeSignByte Size Number of Bits Min ValueMax Value short intSigned unsigned intSigned unsigned ,147,483, ,147,483,647 4,294,967,295 long intSigned unsigned ,147,483, ,147,483,647 4,294,967,295

COMP102 Prog. Fundamentals I: Declarations/ Slide 7 Floating Point A floating-point type is a number with a fractional part, such as The C++ language supports three different sizes of floating-point: float, double and long double. sizeof(float)<= sizeof(double)<= sizeof(long double) float double long double

COMP102 Prog. Fundamentals I: Declarations/ Slide 8 Floating Point typeByte sizeNumber of Bits float432 double864 long double1080 Although the physical size of floating-point types is machine dependent, many computers support the sizes shown below.

COMP102 Prog. Fundamentals I: Declarations/ Slide 9 Declarations l Constants and variables must be declared before they can be used. l A constant declaration specifies the type, the name and the value of the constant. l A variable declaration specifies the type, the name and possibly the initial value of the variable. l When you declare a constant or a variable, the compiler: 1. Reserves a memory location in which to store the value of the constant or variable. 2. Associates the name of the constant or variable with the memory location. (You will use this name for referring to the constant or variable.) l For more on declarations, see and choose English--> C++ --> Declarations.

COMP102 Prog. Fundamentals I: Declarations/ Slide 10 Constant declarations l Constants are used to store values that never change during the program execution. l Using constants makes programs more readable and maintainable. Syntax: const = ; 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$

COMP102 Prog. Fundamentals I: Declarations/ Slide 11 l Variables are used to store values that can be changed during the program execution. l A variable is best thought of as a container for a value y Syntax: ; = ; Examples: int sum; int total = 3445; char answer = ' y ' ; double temperature = -3.14; Variable declarations

COMP102 Prog. Fundamentals I: Declarations/ Slide 12 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. l Variables are not automatically initialized. For example, after declaration int sum; the value of the variable sum can be anything (garbage). l Thus, it is good practice to initialize variables when they are declared. l Once a value has been placed in a variable it stays there until the program deliberately alters it. Variable declarations

COMP102 Prog. Fundamentals I: Declarations/ Slide 13 Character data l A variable or a constant of char type can hold an ASCII character (see Appendix A of the textbook). l 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';

COMP102 Prog. Fundamentals I: Declarations/ Slide 14 Computers are Easy! l "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