Programming in C

1
Programming in C

• Variables, Controls, Functions

2
Different Kinds of Languages

• Java is an object-oriented programming (OOP)
  language
• Problem solving centers on defining classes that
  model things like Trucks, Persons, Marbles,
  Strings, and CandyMachine
• Classes encapsulate data (instance variables) and
  code (methods)
• C is a procedural language
• Problem solving centers on defining functions
  that perform a single service like getValidInt(
  ), search( ) and inputPersonData( ).
• Data is global or passed to functions as
  parameters
• No classes

3
Libraries

• Because Java is an OOP language, its libraries
  consist of predefined classes that you can use in
  your applications
• ArrayList, Scanner, Color, Integer
• Because C is a procedural language, its library
  consists of predefined functions.
• Char/string functions (strcpy, strcmp)
• Math functions (floor, ceil, sin)
• Input/Output functions (printf, scanf)
• On-line C/Unix manual -- the man command
• Description of many C library functions and Unix
  commands
• Usage man ltfunction namegt for C library
  functionsor man ltcommand namegt for Unix commands
• man printf
• man dir
• Search for applicable man pages using the
  apropos command or man -k
• Learn to use the man command using man man

4
Hello World

• In JAVA -- Hello.java is in a class
• package hello
• public class Hello
• public static void main( String args )
• System.out.println( Hello World )
• In C -- Hello.c stands alone
• include ltstdio.hgt
• int main( )
• printf( Hello World\n )
• return 0

5
Compiling and Runninga Java Program
unixgt javac -d . .java
unixgt java hello.Hello
6
Compiling and Running a C Program
unixgt gcc -o hello hello.c
printf.o
Pre- processor (cpp)
Compiler (cc1)
Assembler (as)
Linker (ld)
hello.i
hello.s
hello.o
hello
hello.c
Source program (text)
Modified source program (text)
Assembly program (text)
Relocatable object programs (binary)
Executable object program (binary)
unixgt hello
7
Language Commonality

• C and Java syntax have much in common
• Some Data Types
• Arithmetic operators
• Logical Operators
• Control structures
• Other Operators

8
Data Types

• Both languages support the integral types int,
  short, long.
• Both languages support the floating point types
  double and float
• Both languages support the character data type
  char
• Both languages support enumerations - enum
• C allows the signed (default) and unsigned
  qualifiers for integral types (char, int, short,
  long)
• C does NOT support byte (use char instead)
• Both languages support arrays using and
  indexing starting with zero (0).

9
True and False

• Java supports the bool data type and the keywords
  true and false
• bool isRed true
• bool isLarge false
• C does not support the bool data type. Integer
  variables and expressions are used as instead
• Any non-zero value is considered true
• A zero integer value is considered false
• int isRed 55 / true /
• int isLarge 0 / false /

10
Arithmetic Operators

• Arithmetic operators are the same
• is used for assignment
• , -, (plus, minus)
• , /, (times, divide, mod)
• , -- (increment, decrement (pre and post))
• Combinations are the same
• , -, (plus equal, minus equal)
• , /, (times equal, divide equal, mod
  equal)
• Arithmetic Practice
• Assignment Practice

11
Logical Operators

• Logical operators are the same in C and Java and
  result in a Boolean value.
• (and)
• (or)
• , ! (equal and not equal)
• lt, lt (less than, less than or equal)
• gt, gt (greater than, greater than or equal)
• Boolean Logic Practice

12
Control Structures

• Both languages support these control structures
  which function the same way in C and Java
• for loops
• But NOT -- for (int i 0 i lt size i)
• while loops
• do-while loops
• switch statements
• if and if-else statements
• braces ( , ) are used to begin and end blocks
• Loop Practice

13
Other Operators

• These other operators are the same in C and Java
• ? (tri-nary hook colon)
• int larger (x y ? x y)
• ltlt, gtgt, , , (bit operators)
• ltlt, gtgt, , ,
• (brackets for arrays)
• ( ) parenthesis for functions and type casting
• much more on these later

14
defines

• The define directive can be used to give names
  to important constants in your code. This makes
  your code more readable and more easily
  changeable.
• The compiler replaces every instance of the
  define name with the text that it represents.
• Note that there is no terminating semi-colon
• define MIN_AGE 21
• ...
• if (myAge gt MIN_AGE)
• ...
• define HELP There is no hope
• ...
• printf( s\n, HELP)
• ...

15
typedefs

• C allows you to define new names for existing
  data types (NOT new data types)
• This feature can be used to give
  application-specific names to simple types
• typedef int Temperature
• typedef long Width
• Or to give simple names to complex types - more
  on this later
• Using typedefs makes future changes easier and
  makes the code more relevant to the application

16
Enumeration Constants

• C provides the enum as a list of named constant
  integer values (starting a 0 by default)
• Names in enums must be distinct
• Often a better alternative to defines
• Example
• enum boolean FALSE, TRUE
• enum months JAN 1, FEB, MAR, APR, MAY, JUN,
  JUL, AUG, SEP, OCT, NOV, DEC

17
Miscellaneous

• Comments
• Both languages support block comments surrounded
  by / and /
• C DOES NOT support // comment style
• Declaring variables
• All variables must be declared at the beginning
  of the block in which they are used
• Typecasting
• Both languages allow typecasting - temporarily
  treating a variable as a different type
• temp (double) degrees / 4
• Ask me about C99

18
Functions vs. Methods

• Java classes include methods which can be called
  from any code with appropriate access (recall
  public methods)
• C functions are like Java methods, but they dont
  belong to any class. Functions are defined in a
  file and may be either global to your program or
  local to the file in which they are defined.
• Like Java methods, C functions
• Have a name
• Have a return type
• May have parameters
• Pass arguments by value
• Unlike Java methods, a function in C is uniquely
  identified by its name. Therefore, there is no
  concept of method overloading in C as there is in
  Java. There can be only one main( ) function in
  a C application.
• more on this later

19
C Function Examples

• / returns the average of two integer parameters
  /
• int intAverage( int a, int b )
• return ( (a b) / 2 )
• / Simulates dog barking /
• void bark (int nrTimes)
• int n
• for (n 0 n lt nrTimes n)
• printf(Arf!\n)

20
Function Prototypes

• A function prototype defines the functions name,
  return type, and parameters.
• For example from the previous slide
• void bark( int n )
• int average( int a, int b )
• Before a function may be called, you must provide
  its prototype (or the function definition itself)
  so that the C compiler can verify the function is
  being called correctly.

(note the semi-colon).
21
Recursion

• C functions may be called recursively.
• Typically a function calls itself
• A properly written recursive function has the
  following properties
• A base case - a condition which does NOT make a
  recursive call because a simple solution exists
• A recursive call with a condition (usually a
  parameter value) that is closer to the base case
  than the condition (parameter value) of the
  current function call
• Each invocation of the function gets its own set
  of arguments and local variables

22
Recursion Example

• / print an integer in decimal
• K R page 87 (may fail on largest negative
  int) /
• include ltstdio.hgt
• void printd( int n )
• if ( n lt 0 )
• printf( - )
• n -n
• if ( n / 10 ) / (n / 10 ! 0) -- more than 1
  digit /
• printd( n / 10 ) / recursive call n has 1
  less digit /
• printf( c, n 10 0) / base case --- 1
  digit /

23
A Simple C Program

• / convertTemps.c /
• include ltstdio.hgt / includes prototype for
  printf, etc /
• typedef double Temperature
• / prototype for CtoF /
• Temperature CtoF( Temperature degreesCelsius)
• int main( )
• int temp
• for (temp 0 temp lt 100 temp 20)
• printf(2d degrees F 5.2f degrees C\n,
• temp, CtoF( temp ))
• return 0
• / converts temperature in Celsius to Fahrenheit
  /
• Temperature CtoF(Temperature celsius)

24
Typical C Program
includes
include ltstdio.hgt typedef double
Temperature Temperature CtoF( Temperature
celcius) int main( ) int temp for
(temp 0 temp lt 100 temp 20)
printf(2d degrees F 5.2f degrees
C\n, temp, CtoF( temp )) return 0 /
converts temperature in Celsius to Fahrenheit
/ Temperature CtoF(Temperature celsius)
Temperature fahrenheit fahrenheit 9.0 /
5.0 celsius 32 return fahrenheit
defines, typedefs, data type definitions, global
variable declarationsfunction prototypes
main()
function definitions
25
Compiling on Unix

• Traditionally the name of the C compiler that
  comes with Unix is cc.
• On the UMBC GL systems, use the GNU compiler
  named gcc.
• The default name of the executable program that
  is created is a.out
• unixgt gcc convertTemps.c

26
Compiler Options

• -c
• Compile only (create a .o file), dont link
  (create an executable)
• gcc -c convertTemps.c
• -o filename
• Name the executable filename instead of
  a.outgcc -o project1 convertTemps.c
• -Wall
• Report all warningsgcc -Wall convertTemps.c
• -ansi
• Force adherence to the C ANSI standardsgcc -ansi
  convertTemps
• Use them together
• gcc -ansi -Wall -o project1 convertTemps.c

27
Header Files

• When a file contains functions to be reused in
  several programs, their prototypes and important
  defines are usually placed into a header ( .h )
  that is then included where needed.
• Each .h file should be stand alone. That is,
  it should and defines needed by the prototypes
  and include any .h files it needs to avoid
  compiler errors.
• In this example, the prototype for CtoF() would
  be placed into the file CtoF.h which would then
  be included in convertTemps.c or any other .c
  file that used CtoF( )
• The code for CtoF( ) would be placed int CtoF.c

28
CtoF.h

• / CtoF.h /
• / includes needed by prototypes /
• / relevant defines /
• / relevant typedefs /
• typedef double Temperature
• / prototype for functions defined in CtoF.c /
• Temperature CtoF( Temperature celsius )

29
CtoF.c

• / CtoF.c /
• / necessary includes, defines /
• include CtoF.h
• / converts temp in Celsius to Fahrenheit /
• Temperature CtoF(Temperature celsius)
• Temperature fahrenheit
• fahrenheit 9.0 / 5.0 celsius 32
• return fahrenheit

30
convertTemps.c revisited

• include ltstdio.hgt / note angle brackets /
• include CtoF.h / note quotes /
• int main( )
• int temp
• for (temp 0 temp lt 100 temp 20)
• printf(2d degrees F 5.2f degrees C\n,
• temp, CtoF( temp ))
• return 0

31
Compiling and linking

• When a programs code is separated into multiple
  .c files, we must compile each .c file and then
  combine the resulting .o files to create an
  executable program.
• The files may be compiled separately and then
  linked together. The -c flag in the first two
  command tells gcc to compile only which results
  in the creation of .o (object) files. In the 3rd
  command, the presence of .o extension tells gcc
  to link the files into an executable
• gcc -c -Wall -ansi convertTemps.c
• gcc -c -Wall -ansi CtoF.c
• gcc -Wall -ansi -o myProgram convertTemps.o
  CtoF.o
• Or it can be done all in one step
• gcc -Wall -ansi -o myProgram convertTemps.c CtoF.c

32
Java/C Project example

• Number Theory - a problem about integers
• http//www.cs.umbc.edu/courses/undergradaute/313/f
  all09/code/numbertheory.txt