Lec 08. C Data Types

Lecture 8Lecture 8
Version 1.0Version 1.0
Data Types in CData Types in C

2Rushdi Shams, Dept of CSE, KUET, Bangladesh
Primary Data Types in CPrimary Data Types in C
 We are known of three basic data types in C-We are known of three basic data types in C-
1.1. intint
2.2. floatfloat
3.3. CharChar
 Are they all?Are they all?
 Do the programmers write code with onlyDo the programmers write code with only
these three data types?these three data types?

Additional Data Types in CAdditional Data Types in C
 Answer is NO!!Answer is NO!!
 AA charchar could be ancould be an unsigned charunsigned char or aor a signedsigned
charchar
 intint could be acould be a short intshort int or aor a long intlong int
 Let’s take a deeper look into themLet’s take a deeper look into them

Integers: short and longIntegers: short and long
 The range of integer depends on the compilerThe range of integer depends on the compiler
 Turb C/C++ is a 16 bit compilerTurb C/C++ is a 16 bit compiler
 For such compiler the range of an integer isFor such compiler the range of an integer is
-32768 to 32767-32768 to 32767
 Why such range?Why such range?

 Compiler allocates maximum 16 bits to hold anCompiler allocates maximum 16 bits to hold an
integerinteger
 Then, in that allocated location in memory,Then, in that allocated location in memory,
values up to 2values up to 21515
= 32,768 can be stored= 32,768 can be stored
 If you take both sides (positive and negative)If you take both sides (positive and negative)
then the range will be -32,768 to 32,767then the range will be -32,768 to 32,767
 221515
if 16 bit is allocated, then it should be 2if 16 bit is allocated, then it should be 21616
, no?, no?

 No! Just one bit is preserved to indicate “Signs”-No! Just one bit is preserved to indicate “Signs”-
0 for positive and 1 for negative0 for positive and 1 for negative

 C offers a variation of the integer data type thatC offers a variation of the integer data type that
provides what are calledprovides what are called shortshort andand longlong integer valuesinteger values
 shortshort andand longlong integers would usually occupy two andintegers would usually occupy two and
four bytes respectivelyfour bytes respectively

Integers: longIntegers: long
 longlong variables which holdvariables which hold longlong integers are declaredintegers are declared
using the keywordusing the keyword longlong ––
long int i ;long int i ;
long int abc ;long int abc ;
 They can also be written as –They can also be written as –
long i ;long i ;
long abc ;long abc ;

Integers: longIntegers: long
 longlong integers cause the program to run a bit slower,integers cause the program to run a bit slower,
but the range of values that we can use is expandedbut the range of values that we can use is expanded
tremendously.tremendously.
 The value of aThe value of a longlong integer typically can vary frominteger typically can vary from
-2147483648 to +2147483647-2147483648 to +2147483647

Integers: shortIntegers: short
 integers that need less space in memory and thus helpintegers that need less space in memory and thus help
speed up program execution –speed up program execution –
short int j ;short int j ;
short int height ;short int height ;
 They can also be written as –They can also be written as –
short j ;short j ;
short height ;short height ;
 The range covered by short integers is similar to that ofThe range covered by short integers is similar to that of
integers.integers.

Integers: unsignedIntegers: unsigned
 Sometimes, we know in advance that the valueSometimes, we know in advance that the value
stored in a given integer variable will always bestored in a given integer variable will always be
positivepositive
 In such a case we can declare the variable to beIn such a case we can declare the variable to be
unsignedunsigned, as in,, as in,
unsigned int num_students ;unsigned int num_students ;

Integers: unsignedIntegers: unsigned
 The range will shift from -32768 to +32767 toThe range will shift from -32768 to +32767 to
the range 0 to 65535the range 0 to 65535
 declaring an integer asdeclaring an integer as unsignedunsigned almost doublesalmost doubles
the size of the largest possible value that it canthe size of the largest possible value that it can
otherwise takeotherwise take
 Both are valid syntaxes-Both are valid syntaxes-
unsigned int i ;unsigned int i ;
unsigned i ;unsigned i ;

Integers: unsigned and signedIntegers: unsigned and signed
 Like anLike an unsigned intunsigned int, there also exists a, there also exists a shortshort
unsigned intunsigned int and aand a long unsigned intlong unsigned int..
 By default aBy default a short intshort int is ais a signed short intsigned short int andand
aa long intlong int is ais a signed long intsigned long int

Characters: signed and unsignedCharacters: signed and unsigned
 Parallel toParallel to signedsigned andand unsigned intunsigned ints (eithers (either
shortshort oror longlong), similarly there also exist), similarly there also exist signedsigned
andand unsigned charunsigned charss
 occupying one byte each, but having differentoccupying one byte each, but having different
rangesranges
 How can a character have signed and unsignedHow can a character have signed and unsigned
range?range? We will see that now.We will see that now.

Character: signed and unsignedCharacter: signed and unsigned
 AA signed charsigned char is same as an ordinaryis same as an ordinary charchar andand
has a range from -128 to +127has a range from -128 to +127
 anan unsigned charunsigned char has a range from 0 to 255has a range from 0 to 255

Character: signed and unsignedCharacter: signed and unsigned
 Should this program print the character withShould this program print the character with
corresponding ASCII value of 291?corresponding ASCII value of 291?

Characters: signed and unsignedCharacters: signed and unsigned
 value in our case happens to be 35, hence 35 andvalue in our case happens to be 35, hence 35 and
its corresponding character #, gets printed out.its corresponding character #, gets printed out.

Brainstorming!Brainstorming!

The SolutionThe Solution

Floats and DoublesFloats and Doubles
 AA floatfloat occupies four bytes in memory and can rangeoccupies four bytes in memory and can range
from -3.4e38 to +3.4e38.from -3.4e38 to +3.4e38.
 If this is insufficient then C offers aIf this is insufficient then C offers a doubledouble data typedata type
that occupies 8 bytes in memory and has a range fromthat occupies 8 bytes in memory and has a range from
-1.7e308 to +1.7e308-1.7e308 to +1.7e308
 If the situation demands usage of real numbers that lieIf the situation demands usage of real numbers that lie
even beyond the range offered byeven beyond the range offered by doubledouble data type,data type,
then there exists athen there exists a long doublelong double that can range fromthat can range from
-1.7e4932 to +1.7e4932-1.7e4932 to +1.7e4932

The EssenceThe Essence

ConstantsConstants
 C also allows you to use constants with scientificC also allows you to use constants with scientific
notation. The general form of such notation is-notation. The general form of such notation is-
number E sign exponentnumber E sign exponent
 Please note that there is no space in actual CPlease note that there is no space in actual C
declaration. The spaces are provided to understand thedeclaration. The spaces are provided to understand the
components of such declarationcomponents of such declaration
 The sign part is optionalThe sign part is optional
 1234.56 can be written as 123.456E1 (in everyday math,1234.56 can be written as 123.456E1 (in everyday math,
it is 123.456X101) which is equal to 1234.56it is 123.456X101) which is equal to 1234.56

ConstantsConstants
 C supports another type of constant- the string.C supports another type of constant- the string.
A string is a set of characters enclosed by doubleA string is a set of characters enclosed by double
quotesquotes
 You have worked with strings with printf() andYou have worked with strings with printf() and
scanf(). C allows you to define string constants,scanf(). C allows you to define string constants,
but it does not formally have a string data typebut it does not formally have a string data type
 We will see later that C supports strings withWe will see later that C supports strings with
character arrayscharacter arrays

ConstantsConstants

Type Conversions in ExpressionsType Conversions in Expressions

 What happens here in integral promotion andWhat happens here in integral promotion and
type promotion?type promotion?
100.0/(10/3)100.0/(10/3)

 What happens here in integral promotion andWhat happens here in integral promotion and
type promotion?type promotion?
char ch;char ch;
short i;short i;
unsigned long ul;unsigned long ul;
float f;float f;
f/ch - (i*ul)f/ch - (i*ul)

What is the order then?What is the order then?
1.1. Long doubleLong double
2.2. DoubleDouble
3.3. FloatFloat
4.4. Unsigned longUnsigned long
5.5. LongLong
6.6. UnsignedUnsigned

Type Conversion in AssignmentType Conversion in Assignment
1.1. In an assignment statement (a=b), in which the typeIn an assignment statement (a=b), in which the type
of right side differs with the type of left side, the typeof right side differs with the type of left side, the type
of right side will be converted into the type of the leftof right side will be converted into the type of the left
side.side.
2.2. When the type of the left side is in a better place thanWhen the type of the left side is in a better place than
the type of the right side, there is nothing wrong.the type of the right side, there is nothing wrong.
3.3. But when the type of the right side is in a better placeBut when the type of the right side is in a better place
than the type of the left side, then data loss may occur.than the type of the left side, then data loss may occur.

 When converting from long double to double orWhen converting from long double to double or
double to float, precision is lost.double to float, precision is lost.
 When converting from float to integer,When converting from float to integer,
fractional part is lost.fractional part is lost.
 If the number is too large to fit in the targetIf the number is too large to fit in the target
type, a garbage value will result.type, a garbage value will result.

Type CastType Cast
 Sometimes it is necessary to transform the type of aSometimes it is necessary to transform the type of a
variable temporarilyvariable temporarily
 you want to use a variable in modulus operation, so youyou want to use a variable in modulus operation, so you
have declared it as an integer since modulus operationhave declared it as an integer since modulus operation
never accepts variables other than integersnever accepts variables other than integers
 But you may require using the variable in division asBut you may require using the variable in division as
well which may produce a floating point resultwell which may produce a floating point result
 You can use type cast this timeYou can use type cast this time

Type CastType Cast

Type CastType Cast
 you cannot cast a variable that is on the left side of anyou cannot cast a variable that is on the left side of an
assignment statement.assignment statement.

Lec 08. C Data Types

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Lec 08. C Data Types