copyright © 2007-2010 – curt hill types what they do

Copyright © 2007-2010 – Curt Hill

Types

What they do

Introduction• People are smart, computers are

dumb• This is obvious when we speak

about types• The type is usually understood

when people work in algebra• We do not care if the number is an

integer, fraction or real – it is just a number

• Not so in C++ – we must explicitly state the type


Standard types in C programs

• A type determines legal values and legal operations

• Most of the standard types are reserved words

• In the rest of this presentation the sizes and precisions given are for our machines

• Others compilers may be different


Integer types

• int - a standard integer– Integers in range + or - 2.14 billion– Occupies four bytes

• short - half the size– Range is -32768 to +32767

• long – In our case same as int


Integer Operators

• The integer types allow the standard mathematical operators:– Addition +– Subtraction -– Multiplication *– Integer division /

• 5 / 2 = 2

– Integer remainder %• 5 % 2 = 1


Integer division

• Integer operators always give integer results

• Remembering division and remainder– Do long division– Do not go past the decimal point – Quotient is obtained with /– Remainder with %

• Integer constants are strings of digits with or without a sign


Division operators

• If a is 22 and b is 5• a/b gives 4• a%b gives 2


5 ) 224 r 2

Floating point types

• Also known as real numbers• Consist of exponent and mantissa

– Similar to scientific notation

• Float– Regular floating point numbers– About seven decimal digits

• Double– Twice as many mantissa digits as float– About 14 decimal digits


Constants

• There are two forms for a real constant

• Floating point constants have either a decimal point or an exponent or both

• Scientific notation is something like this: 3.2 × 104

• Since the exponent is hard to type we use E notation:3.2E4


Double Preferred

• Our machines have plenty of memory so saving space is not the issue

• The Pentium only does double arithmetic

• The standard math library accepts only double parameters

• Therefore we routinely use double instead of float


Floating Point Operators

• The real types allow the standard mathematical operators:– Addition +– Subtraction -– Multiplication *– Real division /

• 5.0 / 2.0 = 2.5

– No remainder operator


Overloaded operators

• The / operator is overloaded, which means that it has different meanings depending on what operands it has

• With two integers it means integer division, with two floating point numbers it means real division

• We will later consider what it means when the types do not match


Character types

• Represents an ASCII character• char• One character• Constants are enclosed in single

quotes– As opposed to string constants which

are in double quotes

• Small integers can be used to specify as well


Characters as numbers?

• There is some interchangability between characters and small integers

• Each character is represented on the machine by an integer in the range -128 to +127

• The character set of a machine is the convention that connects the number to the character– We will use ASCII on Windows


Booleans

• Type name is bool• Holds a true or false

– Both are reserved words

• Will discuss this one more seriously later


Modifiers• Before types we can apply several

modifiers that alter some of the characteristics of the type

• long– Usually means that the item is twice as

long as normal for more precision– Not applicable to characters

• short– Usually means that the item is half the

length– Not applicable to characters


More modifiers

• signed– Explicitly must have a sign

• unsigned– May not have a sign– Not allowed on floating point types– Gives one more bit of precision for

integers or characters


Examples

• A double is a long float• Sometimes there is a long double• Characters, may be by default

either signed or unsigned– Ours are signed

• Any particular compiler may ignore some of these


For our purposes we will only consider the

following:• char• int• double• bool


Mixed type expressions

• When an arithmetic expression has two types in it, we call this a mixed type expression

• In general the weaker type is converted to the stronger type and then the operation proceeds

• Shorter items are weaker than longer

• Integer items are weaker than floating


Examples:

• Add a short int to an int– The short int is converted to an int and

the operation proceeds

• Add an int to a float– Convert the int to a float and continue

• To convert: – The original form and value of the

variable are unchanged– For the purpose of the expression

change the value from one type to another


copyright © 2007-2010 – curt hill types what they do

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