CS115 Introduction to Programming

1. CS115 Introduction to Programming Inst. Senem Kumova Metin senem.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 :306

2. WHAT is LANGUAGE ?

3. 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

4. WHAT is a PROGRAMMING LANGUAGE ? A set of rules, symbols, and special words used to construct a computer program

5. 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 )

6. 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.

7. FLOW OF CONTROL SCENARIO : we 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

8. Will we write codes in binary ?? SCENARIO : we 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 1011..0101 10…1010000 100..11100010

9. ASSEMBLY LANGUAGE • Assembly language (or assembler code) was our first attempt at producing a mechanism for writing programs that was more palatable to ourselves ; the easiest way to print "hello, world!" name "hi" org 100h jmp start ; jump over string declaration msg db "hello, world!",0Dh,0Ah, 24h start: lea dx, msg ; load effective address of msg into dx. mov ah, 09h ; print function is 9. int 21h ; do it! mov ah, 0 int 16h ; wait for any key any.... ret; return to operating system. • Of course a program written in assembly code, in order to “run”, must first be translated (assembled) into machine code.

10. HIGH LEVEL LANGUAGE • 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.

11. ASSEMBLY versus HIGH LEVEL LANGUAGE HelloWorld.asm HelloWorld.c ; the easiest way to print "hello, world!" name "hi" org 100h jmp start ; jump over string declaration msg db "hello, world!",0Dh,0Ah, 24h start: lea dx, msg ; load effective address of msg into dx. mov ah, 09h ; print function is 9. int 21h ; do it! mov ah, 0 int 16h ; wait for any key any.... ret; return to operating system. /* easiest way to print “hello, world” */ #include<stdio.h> // library file main() { printf(“hello,world”); }

12. ASSEMBLY versus HIGH LEVEL LANGUAGE HelloWorld.c Source Code HelloWorld.asm Source Code compiled assembled Library (stdio.h) Object Code linked Machine Code (binary) Machine Code (binary)

13. A typical C development environment 1/2 • Phase1. Create a program • Use some editor to create your .c file (emacs, vi, pico etc.) • Save the file in disk • .c file is known as source code • Phase2 and 3. Preprocess and Compile • Preprocessor manipulates program code (examples: includes other files, performs text replacements) • Compiler generates .o file known as the object code • Phase4. Linking • Linker links the library files and creates executable file • To compile your .c file type “gcc –c myfile.c” , this will create .o file • To compile & link type “gcc –o myfile myfile.c” this will create myfile.exe file and executable myfile.exe

14. A typical C development environment 2/2 • Phase5. Loading • Before a program can be executes, it must be first placed to memory by Loader • Phase6. Execution • Under control of CPU, a program may be executed • To load and execute your .exe file type “./myfile”

15. Compilation with gcc compiler in Linux && Execution Step1 : gcc –c myfile.c  myfile.c + myfile.o Step2 : gcc –o myfile myfile.c myfile.c + myfile.o +myfile.exe Step3 : ./myfile or Step1 : gcc –c myfile myfile.c  myfile.c +myfile.exe Step2 : ./myfile • You may use also cc compiler instead of gcc

16. 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.

17. 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++…..

18. A SHORT BREAK ! 20 min …

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

20. Learn printf #include <stdio.h> // library file void main(void) { printf("from sea to shining C\n"); }

21. Learn printf #include <stdio.h> void main(void) { printf("from sea ”); printf(“to shining C\n"); }

22. Learn printf / scanf #include <stdio.h> void main(void) { int x=0; printf(“x= %d”,x); // print x = 0 scanf(“%d”,&x); /* scan the value from screen and assign this value to x */ printf(“%d”,x); }

23. Comments /* Ignored part by the compiler */ // Ignored part by the compiler (only this line) void main() { //….. }

24. Comments • Comments are arbitrary strings of symbols placed between the delimiters /* and */ • Comments are not tokens but white spaces for the C compiler a) /* a comment */ c)   /**********    *  a comment *    ************/ b)    /*     * a comment     */ d)  /*************/      /*  a comment */    /*************/

25. 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 operator kurus=56; // Assignment printf(“ Money is %d lira %d kurus\n”, lira, kurus); // printf statement toplam_kurus = lira*100+ kurus; printf(“ \n Total kurus is %d kurus\n”, toplam_kurus); // first part of the printf statement is a control string }

26. Variables and Assignment OUTPUT: Money is 13 lira 56 kurus Total kurus is 1356 kurus

27. 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 3.14 void main(void) { printf(“PI equals : %f\n”,PI); // %f is used for floating numbers }

28. If Statements C CODE void main() { int x; int y; if( x>0) x=y+1; else x=y-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

29. 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(a>b) return a; else return b; }

30. 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 FUNCTION printf("Maximum = %d",max); // PRINT THE OUTPUT } int mymaximum( int a , int b) // DEFINE SUB-FUNCTION { if(a>b) return a; else return b; }