Senem Kumova Metin

CS115 Introduction to Programming

Inst. Senem Kumova Metinsenem.kumova@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 event

WHAT 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 > 0

YES NO

x = y+1 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

000…110001

100010….01

YES NO

10…1010000 1011..0101

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:

1. Interpretation, and

2. 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 / scanfIncluding librariesWriting commentsDefining variables ….if statements

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Learn printf

#include <stdio.h> // library file

void main(void)

{

printf("from sea to shining C\n");

}

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Learn printf

#include <stdio.h>

void main(void)

{

printf("from sea ”);

printf(“to shining C\n");

}

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Learn printf / scanf#include <stdio.h>void main(void){

int x=0;printf(“x= %d”,x); // print x = 0scanf(“%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

d)  /*************/      /*  a comment */    /*************/

b)    /*     * a comment     */

c)   /**********    *  a comment *    ************/

a) /* a comment */

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Variables and Assignment

#include<stdio.h>void main(void){ int kurus; // declarations of variables (int is a keyword, takes integer values)int lira=0; // declaration and initialization of a variable int toplam_kurus; lira =13; // Assignment statement, “=“ is the assignment operatorkurus=56; // Assignment

printf(“ Money is %d lira %d kurus\n”, lira, kurus); // printf statementtoplam_kurus = lira*100+ 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 */

#include<stdio.h>#define PI 3.14void main(void){ printf(“PI equals : %f\n”,PI);// %f is used for floating numbers}

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If Statements

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

C CODE

void main()

{ int x; int y;

if( x>0)

x=y+1;

else

x=y-1;

printf(“%d”, x); }

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if statements

int mymaximum( int a , int b)

{ if(a>b)

return a;

else

return b; }

MISSION :

Write a function called mymaximum that

gets 2 integer values (as input parameters) and returns

back the greater one

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Functions and if statements

#include <stdio.h>

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 FUNCTIONprintf("Maximum = %d",max); // PRINT THE OUTPUT}

int mymaximum( int a , int b) // DEFINE SUB-FUNCTION{ if(a>b) return a;

else return b; }