C ????

1
C ????

• Learn how to write C programs
• Data Types
• Program Structures
• Input/Output and Files
• Preprocessing
• Compile ? Link ? Execute (Visual C 6.0)

2
C Programming Language Introduction 1
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• Information about the course
• 1 hour lecture 2 hours lab per week
• Lab Attendance and Performance 10
• 8 laboratory assignments 20
• 1 midterm examination 30
• 1 final examination 30
• Textbook Teach Yourself C, 3rd Edition by
  Herbert Schildt, McGraw-Hill, Inc., 1999 (ISBN
  0-07-882311-0).
• A copy of slides extra materials are
  available from http//www.cs.ccu.edu.tw/pahsiung
  /courses/introCS/

3
C Programming Language Introduction 2
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• General information
• A programming language is a language that is
  used by a person to express a process by which a
  computer can solve a problem
• A language is organized around a particular
  conceptual model - once a language has been
  developed conceptually, it must be implemented
• Implementation of a language means that its
  basic structures should be represented at the
  level of bits
• A programming language is an abstraction which
  expresses the steps of specification in the form
  which is converted by translator into set of
  computer instructions

4
C Programming Language Introduction 3
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• Programming languages
• studying. What are the aims?
• to understand better the functioning and
  implementation of the structures in different
  languages
• to choose a suitable language for the project
  (two different classes of problems may require
  different levels of abstraction)
• to learn new capabilities of existing languages
• Classification of languages
• imperative languages (e.g. Pascal, C/C,
  Fortran)
• non-imperative languages (e.g. Prolog, LISP)

5
C Programming Language Introduction 4
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• Translation process and its main stages
• (all stages are machine-dependent)
• lexical analysis (scanning) identifies sequences
  of characters (tokens) which represent values,
  identifiers, operators, etc.
• syntactic analysis (parsing) identifies valid
  sequences of characters (statements, expressions)
  and rejects invalid ones
• semantic analysis assigns a meaning to
  identified entities
• Translators can be in the form of interpreter
  or compiler (in most cases when semantic
  analysis is finished compilers perform code
  optimization)

6
C Programming Language Introduction 5
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• Compilation, linking loading
• Compiling is a process of translation of a
  source code into machine-dependent object code
• Linking is a process which combines two or more
  separate object programs and supplies the
  information needed to resolve references between
  them (independently compiled code is linked
  into a single load module)
• Loading is a process which brings the object
  program into memory and starts its execution
• Modern programming environments combine a set of
  tools (editor compiler linker loader
  testing tools ) into a unique package

7
C Programming Language Introduction 6
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• Compilation, linking loading
• Many programming languages allow You to write
  different pieces of code (modules) separately,
  and after their compilation linker put these
  modules together
• Linker also replaces symbolic addresses with
  real memory addresses
• Library is a set of precompiled routines that
  are stored in the object format
• Loader is an OS utility (mostly, You cant
  directly execute it) that copies programs from
  the storage device to the main memory, adjusting
  properly addresses

8
C Programming Language Introduction 7
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• Language portability
• A language is portable if its programs can be
  compiled and run on different types of computers
  without rewriting a source code
• C is potentially one of the most portable
  programming languages. Most C compilers (Borland,
  Microsoft, Symantec, Watcom, etc.) provide useful
  extentions (additional features) that are not a
  part of the C standard
• Organizations which prepare and revise standards
  for languages
• American National Standards Institute
  (ANSI)
• International Standards Organization (ISO)
• Institute of Electrical and Electronics
  Engineers (IEEE)

9
C Programming Language Introduction 8
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• Brief comments on C
• C language ? extensions C with classes
  (Bjarne Stroustrup) ? C language (1984)
• C sits on the shoulders of C language (from a
  B.Stroustrups keynote address to ANSI C
  committee in 1989 C is an engineering
  compromise, and it must be kept as close as
  possible to C, but no closer)
• C ? (power and efficiency of C) features
  that support object-oriented programming (OOP)
  type safety high expressiveness
• C is quite complex and more difficult to
  master than C
• C introduces a new paradigm (model of
  programming)

10
C Programming Language Introduction 9
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• Brief comments on C
• At the same time, C fully supports traditional
  procedural programming style (process-oriented
  paradigm) - it means that C is a multiparadigm
  programming language
• I know C, so C is somewhat clear as well?
  Unfortunately, NOT exactly Most probably, You
  know ANSI C subset of C (even without clear
  understanding of C and C incompatibilities!)
• The main concepts of Object-Oriented Programming
  (OOP)
• ? Data Abstraction ?
  Class/Object
• ? Encapsulation
  ? Inheritance

11
C Programming Language Introduction 10
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• Brief comments on C
• If You want to know more about history of C,
  see the following book
• The Design and Evolution of C
  by B.Stroustrup
• (1994, Addison-Wesley)
• 
  Further reading
• Practical C Programming
  (Nutshell Handbook) by
• S.Qualline (1995, OReilly
  Associates)
• The C Programming Language by
  B.Stroustrup
• (2000, Addison-Wesley)
• 
  Now we start with C language...

12
C Programming Language Introduction 11
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• Origins of C language
• 1964-1970 Basic Combined Programming Language
  (BCPL), project Multics (UNIX operating system)
• 1970-1973 NB (New B) as a modification of B
  language and appearance of C language (Dennis
  Ritchie)
• 1973-1978 the kernel of OS UNIX for PDP-11 was
  rewritten in C changes in the language and
  appearance of the first book on C (The C
  programming language by B.Kernighan and
  D.Ritchie it is now known as KR C)
• 1978-1985 C compilers became available on
  different machine architectures
• 1983-1990 ANSI established committee X3J11 with
  a goal of producing a C standard (standard
  ISO/IEC 9899-1990)

13
C Programming Language Introduction 12
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• C language keywords
• C is very compact language (32 keywords in ANSI
  C 27 keywords in KR C 5 keywords which were
  added by ANSI committees)
• auto break case
  char const
• continue default do
  double else
• enum extern float
  for goto
• if int
  long register return
• short signed sizeof
  static struct
• switch typedef union
  unsigned void
• volatile while
• 
  All keywords are lowercase!

14
C Programming Language First examples 1
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• 
  Example 1
• includeltstdio.hgt / C /
• int main(void)
• printf(the\n first\n program in
  course)
• return 0
• includeltiostream.hgt // C this is
  one line comment
• int main( )
• cout ltltthe\n first\n program ltlt
  in course ltlt endl
• return 0

15
C Programming Language First examples 2
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• includeltstdio.hgt
  Example 1A
• int main(void)
• printf(the first output line.)
• printf(the second output line)
• return 0
• includeltstdio.hgt
  Example 2
• int main(void)
• int my_variable 65
• printf(the value is d\n,
  my_variable)
• printf( and the other result is
  c, my_variable)
• return 0

16
C Programming Language First examples 3
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• printf(the value is d\n,
  my_variable)
• includeltstdio.hgt
  Example 3
• main(void)
• int i 0
• while(i lt 9)
• if(i 5) continue
• printf(the result is
  d,i)
• return 0

format specifier
list of variables
control string
PAY attention !
17
C Programming Language First examples 4
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• 
  Example 3A
• include ltstdio.hgt
• int main(void)
• int sqrs10
• int i
• for(i1 ilt11 i) sqrsi-1
  ii
• for(i0 ilt10 i)
• printf(d ,
  sqrsi)
• return 0

array sqrs consists of 10 elements
indices start with 0 !
18
C Programming Language First examples 5
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• includeltstdio.hgt
  Example 4
• includeltstring.hgt
• int main(void)
• int index
• char stuff15, pt
• strcpy(stuff,Test string)
• pt stuff
• / character by
  character printing of string /
• for(index 0 index lt 15
  index)
• printf(_ c,
  pt) pt
• return 0

PAY attention !
result _T_e_s_t_
_s_t_r_i_n_g_._._._
19
C Programming Language First examples 6
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• 
  Example 4A
• includeltstdio.hgt
• int a,b,c
• int sum(int x, int y)
• int main(void) / simple program
  calculates /
• / the sum of two
  integers /
• printf(enter the 1st number )
• scanf(d, a)
• printf(enter the 2nd number )
• scanf(d, b)
• c sum(a,b) / a call to
  the function sum( ) is done here /
• printf(\nthe result of d d
  is d\n, a,b,c)
• return 0
• / definition of the function which
  calculates a sum of two integers /
• int sum(int x, int y)
• return(xy) / end of
  the functions body /

function prototype provides the C compiler with a
necessary information about the function
PAY attention ! (absence of semicolon)
20
C Programming Language Explanations 1
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• Functions are central to C/C programming
• A function is an independent section of program
  code that performs a certain task and has been
  assigned a name
• Function main( ) is the only component which is
  required in every C/C program

Library functions (purchased as a part of the C
compiler package or from the other vendors)
Functions
User-defined functions (created by a programmer)
21
C Programming Language Data Types 1
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• Concept of data types determines
• a set of values of objects (variables) of
  particular type
• a set of operations which can be applied to these
  objects (their values)
• the size of memory used for storing the values of
  objects
• the way a bits combination which corresponds to
  internal representation of values is interpreted
• 5 basic types in C language
• char int float
  double void
• 4 format modifiers signed unsigned
  short long

22
C Programming Language Data Types 2
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• Some useful remainders on types...
• different values have varying memory storage
  requirements
• the size of the data types can vary depending on
  the computer platform used
• ANSI guarantees the following simple rules
• sizeof(char) ? 1 byte
• sizeof(short) ? sizeof(int), short ? short
  int
• sizeof(int) ? sizeof(long), long ? long int
• sizeof(unsigned) ? sizeof(int), unsigned ?
  unsigned int
• sizeof(float) ? sizeof(double)
• before a variable is used in a C program, it must
  be declared
• typename variable_name

23
C Programming Language Data Types 3
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• typedef and constants...
• by means of using keyword typedef a new name
  (synonym) for existing type is created (note, NOT
  a new type! )
• typedef int integer /
  integer is synonym for int /
• integer my_variable 15
• / the variable is defined - that is,
  declared and initialized /
• the value stored in a constant (unnamed constant)
  cant be changed during programs execution
• 0.123
• 15.
• -7.139
• floating-point constants can be written in
  scientific notation as well (1.12e-3 ? 0.00112)

literal floating-point constants are treated by
C compiler as a double-precision numbers
24
C Programming Language Data Types 4
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• more on constants
• a literal constant written without decimal point
  is represented by the compiler as an integer
  constant
• -11
• 153
• 638
• 043
• 0x84
• 0X137
• const long tum 12345678

decimal integer constants
octal (base 8) integer constant start with a
leading zero (0)
hexadecimal (base 16) integer constants start
with a leading 0x or 0X
tum is a symbolic constant
25
C Programming Language Data Types 5
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• more on constants and types
• C compiler fits a numeric constant into a
  smallest compatible data type, but a programmer
  can specify a desired type explicitly by using a
  suffix notation
• 135
• 135U (135u)
• 135UL (135ul)
• 135.17
• 135.17F (135.17f)
• In C programs You can use three floating-point
  types float, double and long double (the
  default working type in C is double)

constant of the type int (by default)
constant of the type unsigned int
constant of the type float
?
26
C Programming Language Data Types 6
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• more on constants and types
• 
  Example 4A
• includeltstdio.hgt
• int main(void)
• printf(the first result is .11f\n,
  135.1737f/34)
• printf(the second result is .11f,
  135.1737/34)
• return 0
• float type provides 6-7 significant digits
  (precision) mantissa - 23 bits
• double type - 15-16 significant digits
  (precision) mantissa - 52 bits

format specifier f stands for both float
and double values
result the first
result is 3.97569723690 the second result is
3.97569705882
27
C Programming Language Data Types 7
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• more and more on constants and types
• 
  Example 5
• includeltstdio.hgt
• int main(void)
• int variable 15
• printf(1. result d o\n,
  012variable, 12variable)
• printf(2. result d\n,
  0xAvariable)
• printf(3. result x o, 015,
  0Xd)
• printf(\n4. result X, 10)
• return 0
• x (X) means that a
  corresponding
• hexadecimal value is displayed
  with a prefix
• 0x (0X) o for octal values
  brings prefix 0

PAY attention to the hash mark
(pound sign) in format specifiers
result 1. result 150 264 2. result
150 3. result 0xd 015 4. result 0XA
28
C Programming Language Data Types 8
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• even more on constants and types
• enumeration - a set of symbolic constants (named
  integers) which form all the valid values of
  declared type
• enum game socker, cricket, golf, baseball var1,
  var2
• tag and list of variables are optional
• the previous declaration means that variables
  var1 and var2 are of the type enum game and their
  possible values are listed as enumerators (see
  the list in curly brackets)
• each enumerator internally is represented as an
  integer constant value (by default, socker ? 0,
  cricket ? 1, etc.)

list of variables
list of enumerators
tag
keyword
29
C Programming Language Data Types 9
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• much more on constants and types
• default correspondence of enumerators to integers
  can be changed explicitly
• enum game socker, cricket 10, golf,
  baseball -5
• enum game var1, var2
• .. .. .. .. .. .. ..
• printf(output is d and d,
• 
  socker, baseball)
• printf(what is it? s,
  golf) ..
• (!) specifier s determines a format of
  character string

stands for 11 (the previous value 1)
values 0 and -5 appear in the output
requires stdio.h header file
something very strange (garbage) in the output
...
30
C Programming Language Data Types 10
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• much more on constants and types
• String constant is a sequence of characters
  enclosed in a pair of double quotes ()
• String ( VAR a string25 ) data type
  which is supported by Turbo Pascal is formally
  absent in C language
• m ? character constant (enclosed in single
  quotes)
• m ? string constant (internally represented
  by 2 bytes)
• example/goes on ? string constant
  (recognized by the C compiler
• as a
  single token)
• \n ? backslash character constant (escape
  sequence) which represents
• newline (recognized as a single
  token)
• \b - backspace \ - double quote
• \t - horizontal tab \0 - nul character
  (ASCII code 0)
• \\ - backslash \a - alert (speaker
  single beep)

31
C Programming Language Data Types 11
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• escape sequences in brief
• 
  Example 5A
• include ltstdio.hgt
• main (void) / function main( ) returns
  the value of type int by default /
• printf(the value of constants
  are c and c\n, \x41,\60)
• / hexadecimal and octal escape sequences are
  used in printf( ) /
• / \60 can be written as \060 /
• printf (ASCII code is d \n,\n)
• / ASCII code of character \n is 10 (decimal)
  or A (hexadecimal) /
• printf (\ the first line of text \\xA\ and
  the second one\\n)
• / escape sequence \(double quotes) is used in
  printf( ) /
• printf (\a1\\2\nabc\b\bde\n)
• / escape sequence used \a (alert - short
  beeping from systems speaker), \b (backspace -
  cursor moves one position back in the line) /
• return 0

32
C Programming Language Data Types 12
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• much more on constants and types
• 
  Example 6
• include ltstdio.hgt
• int main(void)
  
  
• int abc 11100 / 2 bytes on
  16-bit computers /
• printf (multiplication 1 d\n,
  3abc)
• printf (multiplication 2
  ld\n,3abc)
• printf (multiplication 2 u\n,
  3abc)
• printf (multiplication 2 u\n,
  3uabc)
• printf (multiplication 3
  ld\n, 3Labc)
• return 0
• 
  

PAY attention to the comment...
binary representation of 33,300 (2 bytes)
?
33
C Programming Language Data Types 13
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• 
  Example 7
• include ltstdio.hgt
• int main (void)
• pri / a comment / ntf (be ready
  for ERROR \n)
• / ERROR Undefined symbol pri most probably the
  error message will be not
• the only one at the stage of compilation /
• printf (one string goes on
  here\n)
• / two string will be concatenated by compiler
  into single string - original C
• did not support it, this was a new feature in
  ANSI C /
• printf (result is d, sizeof
  a)
• / string constant a is an array consisting of
  two elements /
• printf (\nthe result in the program
  f\n, 100.154)
• printf (compare d and d, sizeof
  (100.154),
• sizeof (100.15f4)) ...

34
C Programming Language Data Types 14
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• much more on constants and types
• specifier d signals the printf( ) function to
  get a decimal value and output it (see the
  previous example ...)
• for printf( ) statement its very important that
  the number of format specifiers (placeholders)
  corresponds exactly to the number and types of
  the variables in the output list, that is
• printf( . _ .. _ . , ,
  )
• C language does NOT CONTAIN I/O functions to read
  from the keyboard and write to the screen -
  standard library function printf() provides a
  formatted console output (the prototype of this
  function is given in stdio.h header file)

35
C Programming Language Data Types 15
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• symbolic constants and output
• 
  Example 8
• define TRUE 1
• define FALSE 0
• includeltstdio.hgt
• typedef int boolean
• int main(void)
• boolean a
• a TRUE
• / some other statements are
  included here /
• printf("the value of a in different formats\n"
• "d\n04d\n4d",
  a, a, a)
• return 0

preprocessor directives
TRUE and FALSE are symbolic constants
string (text) 1 is associated with a name TRUE
a new name boolean is introduced
for the existing type int
What is printed? 1 0001 1
Pay attention to the presence of sign!
36
C Programming Language Data Types 16
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• more on symbolic constants
• different specifiers and modifiers used in calls
  to the function printf() are covered by the
  examples throughout the course
• example 9 (see the lecture notes on the Web
  site) is left for self-studying
• 
  Example 10
• includeltstdio.hgt
• define TRUE 1
• define FALSE 0
• int main(void)
• int input_var
• scanf(d, input_var)
• / .. some fragment of
  the program .. /
• if ((input_var TRUE)
  (input_var FALSE))
• printf(\nthe value of
  input_var is hu or hu, TRUE, FALSE)
• return 0

what result directive define TRUE 1 brings?
dont forget
hu stands for short unsigned integer
37
C Programming Language Data Types 17
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• type conversions
• if in the expression an operator is applied to
  two variables of the same type, the result is
  quite clear but if these variables are of
  different types, unexpected results can occur
  (the last case is prohibited by many programming
  languages, but in C language its possible)
• in general, if two different types are mixed
  in the expression, the most restrictive type is
  converted to the least restrictive
• type conversion (promotion) may bring
• a) type extension
• b) truncation
• c) problems !! (this happens when conversion
  does
• not make too
  much sense)
• type CASTING in C language (type)
  expression

this is discussed in the following examples
38
C Programming Language Data Types 18
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• type conversions
• suppose the following declaration part
• char ch A
• short sv 987
• int iv
• double dv
• and expressions which are built on declared
  (defined) variables - after automatic (IMPLICIT)
  conversions the types of expressions are as
  follows
• sv - ch 5
• dv ch
• iv dv
• iv/ch

ASCII code of the character A (uppercase) is 65
variables ch and sv are initialized
type int
sv and ch are automatically converted to int
(integral promotion)
type double
type int
type int (integer division takes place)
39
C Programming Language Data Types 19
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• more on type conversions
• Assume that the type int occupies 2 bytes (this
  is the case for 16-bit computers). What is
  printed on the screen?
• printf(the first result is u\n,
  chsv)
• printf(the second result is d,
  chsv)
• the range of int type values is -32,768
  32,767
• the type of the arithmetic expression chsv is
  unsigned int (ch is promoted to int, sv is
  promoted to int as well, but the result 64155 of
  multiplication is too big to fit the int type
  range, so it is promoted to unsigned int)

dont forget this assumption !
?
40
C Programming Language Data Types 20
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• explicit conversion or casting
• what happens when CASTING (EXPLICIT conversion)
  is applied?
• (double)sv - ch 5
• (int)(dv ch)
• iv iv/(float)ch

integral promotion takes place (ch is converted
to int type)
casting - sv is explicitly converted to double
expression of the type double
type int
floating-point division takes place
type int
fractional part is lost
41
C Programming Language Data Types 21
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• implicit conversion casting
• 
  Example 11
• includeltstdio.hgt
• int main(void)
• char object_ch
• const int object_int 300 /
  const modifier is used /
• float object_f 12.75389
• unsigned object_un 50000
• object_ch object_int
• / automatic (implicit) type conversion
  takes place here /
• printf(the result A is d,
  object_ch)
• object_ch object_un
• printf(the result B is
  d, object_ch)
• object_un object_f
• printf(\nresult C is
  u, object_un)
• return 0

variable object_ch is declared of the type
char Pay attention to the way it is used in
the program
Explanations are given on the next slide...
42
C Programming Language Data Types 22
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• implicit conversion casting

1 byte (char type object)
binary representation of the value (300) of the
variable object_int
50000 (unsigned int value)
schematical explanation of the example 11 (see
the previous slide)
43
C Programming Language Data Types 23
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• more on conversions
• the representation of a data object is the
  particular pattern of bits in the memory a
  conversion of a value from one type to another
  one may or may not involve a representation
  change
• in INTEGRAL EXPRESSIONS only objects of types int
  and long (possibly, unsigned) are used
• char a / suppose some value is
  assigned /
• long b / suppose some value is
  assigned to b as well /
• what is the result type of the expression
  ab?
• (1) char type is converted to the type int
  (UNARY CONVERSION)
• (2) one operand is of the type long, the other
  one - int
• ? conversion results in the long type
  (BINARY CONVERSION)

44
C Programming Language Data Types 24
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• implicit conversion casting
• 
  Example 12
• includeltstdio.hgt
• int main(void)
• int a 1740, b 150
• double x char c b
• x a/b
• x a/(bc)
• x a/(b(double)c)
• x (double)a/b
• a (int)x/4
• (int)x a/b
• x c
• printf(d\td,
  sizeof(c2), sizeof((char)(c2)))
• return 0

7.0
examples of casting
7.01613
operator sizeof returns a value of unsigned
integer type which represents a size (in bytes)
of its (operators) operand
ERROR! (lvalue is expected!)
45
C Programming Language Data Types 25
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• some comments on the type void
• type void is a type with NO values and NO
  operators
• its primary fields of use
• (1) to show that a function DOES NOT RETURN a
  value
• (see procedures in the other programming
  languages)
• (2) to ignore a functions return value
  (although it is not necessary
• to do)
• (void)printf(something)
• function printf( ) returns a number of
  characters successfully written to the standard
  output - yes, yes, we know this fact, but we
  ignore (discard) a returned value

Dont be surprised by casting!...
46
C Programming Language Data Types 26
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• promotion with sign extension
• 
  Example 12A
• includeltstdio.hgt
• int main(void)
• char ch1 100
• char ch2 200
• char ch3 ch1 ch2
• printf(ch1 d\n, ch1)
• printf(ch2 d\n, ch2)
• printf(ch3 d\n, ch3)
• return 0

we assume that char is signed char
when a variable of an integral type narrower
than int is used in the expression, it is
promoted to int (or unsigned int, if needed)
conversion of ch1, ch2 and ch3 to int is done
before printf( ) uses them
See the next slide...
47
C Programming Language Data Types 27
Prepared by Dr.Konstantin Degtiarev, 11.02.2000
promotion with sign extension
1 byte for ch2 (200)
output ch1 100 ch2 -56
ch3 44
output ch1 100 ch2 200
ch3 44
Suppose the following changes are done
.. unsigned char ch1 100
unsigned char ch2 200
unsigned char ch3 ch1 ch2 ..
48
C Programming Language Data Types 28
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• promotion with sign extension
• Why the result of printf statements look like
  this?

Promotion still preserves the sign (all
variables are unsigned)
49
C Programming Language Data Types 29
Prepared by Dr.Konstantin Degtiarev, 11.02.2000
Unsigned characters box
Borland C 3.1
Code Generation options in Borland C 3.1 and 5.0
Borland C 5.0
50
C Programming Language Data Types 30
Prepared by Dr.Konstantin Degtiarev, 11.02.2000

• finally, the last slide on Data Types
• 
  Example 13
• includeltstdio.hgt
• int main(void)
• long double a 300.123456789
• float c
• char d
• printf(1 result .9Lf\n, a)
• / format modifier L stands for
  long double type /
• c a
• d a c / this this the
  example of multiple assignment /
• printf(2 result .9f\n, c)
• printf(3 result c,
  d)
• return 0

output 1 result 300.123456789 2
result 300.123443604 3 result ,
!
?