CS115 Introduction to Programming

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CS115 Introduction to Programming

• Inst. Senem Kumova Metin
• senem.kumova_at_ieu.edu.tr
• Textbook A Book on C, A. Kelly and I.Pohl
• Lecture Notes http//homes.ieu.edu.tr/skumova/
  
• Office hours TBA
• Office 408

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WHAT is LANGUAGE ?
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WHAT is PROGRAMMING??scheduling or performing a
task or / and eventWHAT is COMPUTER
PROGRAMMING??creating a sequence of steps for a
computer to follow in performing a task
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WHAT is a PROGRAMMING LANGUAGE ?
A set of rules, symbols, and special words used
to construct a computer program
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Programming language rules consist of Rules of
Syntax which specify how valid instructions are
written in the language(like natural language
rules? subject verb object ) Rules of
Semantics which determine the meaning of the
instructions (what the computer will do)(like
natural language rules? A book has bitten a car )

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A COMPUTER PROGRAM ?

• A set of machine instructions which in turn are
  represented as sequences of binary digits
  (0001010.111011)
• The execution sequence of a group of machine
  instructions is known as the flow of control.

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FLOW OF CONTROL

• SCENARIO
• you have 2 integers x,y
• if x is greater than 0 then
• do x y 1
• else
• do x y-1
• print the value of x

int x and int y
x gt 0
YES
NO
x y1
x y-1
print x
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Will we write codes in binary ??

• SCENARIO
• you have 2 integers x,y
• if x is greater than 0 then
• do x y 1
• else
• do x y-1
• print the value of x

000110001
100010.01
YES
NO
1011..0101
101010000
100..11100010
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ASSEMBLY LANGUAGE

• Assembly language (or assembler code) was our
  first attempt at producing a mechanism for
  writing programs that was more palatable to
  ourselves

movl 0x1,n compare cmpl oxa,n cgt
end_of_loop acddl 0x1,n bra
compare end_of_loop

• Of course a program written in assembly code, in
  order to run, must first be translated
  (assembled) into machine code.

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HIGH LEVEL LANGUAGE

• From the foregoing we can see that assembler
  language is not much of an improvement on machine
  code!
• A more problem-oriented (rather than
  machine-oriented) mechanism for creating computer
  programs would also be desirable.
• Hence the advent of high(er) level languages
  starts with the introduction of Autocodes, and
  going on to Algol, Fortran, Pascal, Basic, Ada,
  C, etc.

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PROGRAM PROCESSING

• A program written in a high level language
  (source code) can only be run in its machine
  code equivalent format.
• SOURCE CODE ? MACHINE CODE
• There are two ways of achieving this
• Interpretation, and
• Compilation

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1. INTERPRETATION

• Interpretation requires the use of a special
  program that reads and reacts to source code.
• Such a program is called an interpreter.
• During interpretation run-time errors may be
  detected and meaningful error messages produced.

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2. COMPILATION

• Compilation requires the use of a special program
  (called a compiler) that translates source code
  into object code.
• SOURCE CODE ? OBJECT CODE
• Sometimes various library files must be linked
  in using another special program called a
  linker, which produces executable code.
• OBJECT CODE ? MACHINE CODE

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LIBRARIES

• Libraries (in computer programming terms) contain
  chunks of precompiled (object) code for various
  functions and procedures that come with a
  programming language that requires compilation
• For example functions and procedures to
  facilitate I/O.

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Why C?

• Native language of UNIX
• Standard development language for personal
  computers
• Portable (can be moved to other machine !)
• Powerful set of operators and powerful libraries
  (some operators ,--.)
• Basis for Java, C..

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• A SHORT BREAK !
• 20 min

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INTRODUCTION TO C

• Your First C programs
• Basic I/O functions printf / scanf
• Including libraries
• Writing comments
• Defining variables .
• if statements

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Learn printf

• include ltstdio.hgt // library file
• void main(void)
• printf("from sea to shining C\n")

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Learn printf

• include ltstdio.hgt
• void main(void)
• printf("from sea )
• printf(to shining C\n")

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Learn printf / scanf

• include ltstdio.hgt
• void main(void)
• int x0
• printf(x d,x) // print x 0
• scanf(d,x) / scan the value from
  screen and assign this value to x /
• printf(d,x)

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Comments

• / Ignored part by
• the compiler /
• // Ignored part by the compiler (only this line)
• void main()
• //..

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Comments

• Comments are arbitrary strings of symbols placed
  between the delimiters / and /
• Comments are not tokens but white spaces for the
  C compiler

c)   /      a comment    
/
a) / a comment /
d)  //      /  a comment /   
//
b)    /     a comment     /
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Variables and Assignment

• includeltstdio.hgt
• void main(void)
• int kurus // declarations of variables (int is a
  keyword, takes integer values)
• int lira0 // declaration and initialization of
  a variable
• int toplam_kurus
• lira 13 // Assignment statement, is the
  assignment operator
• kurus56 // Assignment
• printf( Money is d lira d kurus\n, lira,
  kurus) // printf statement
• toplam_kurus lira100 kurus
• printf( \n Total kurus is d kurus\n,
  toplam_kurus)
• // first part of the printf statement is a
  control string

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Variables and Assignment

• OUTPUT
• Money is 13 lira 56 kurus
• Total kurus is 1356 kurus

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The use of define

• / Lines starting with are called preprocessing
  directives
• Preprocessor first changes all occurences of
  identifier PI to 3.14 /
• includeltstdio.hgt
• define PI 3.14
• void main(void)
• printf(PI equals f\n,PI)
• // f is used for floating numbers

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If Statements
C CODE void main() int x int y
if( xgt0) xy1 else xy-1
printf(d, x)

• SCENARIO/ MISSION
• you have 2 integers x,y
• if x is greater than 0 then
• do x y 1
• else
• do x y-1
• print the value of x

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if statements
MISSION Write a function called mymaximum that
gets 2 integer values (as input parameters) and
returns back the greater one

• int mymaximum( int a , int b)
• if(agtb)
• return a
• else
• return b

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Functions and if statements

• include ltstdio.hgt
• int mymaximum(int a, int b) // FUNCTION
  PROTOTYPE
• void main(void)
• int max, x, y 7 // DECLARE 3 VARIABLES,
  INITIALIZE Y
• printf("please give the value for x ")
• scanf("d",x) // GET THE VALUE OF VARIABLE X
• max mymaximum(x,y) // CALL TO THE MYMAXIMUM
  FUNCTION
• printf("Maximum d",max) // PRINT THE OUTPUT
• int mymaximum( int a , int b) // DEFINE
  SUB-FUNCTION
• if(agtb) return a
• else return b