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 : 408

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 : 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

8. 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 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 movl #0x1,n compare: cmpl #oxa,n cgt end_of_loop acddl #0x1,n bra compare end_of_loop: • Of course a program written inassembly code, in order to “run”, must first be translated (assembled) into machine code.

10. 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.

11. 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

12. 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.

13. 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

14. 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.

15. 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++…..

16. A SHORT BREAK ! 20 min …

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

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

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

20. 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); }

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

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

23. 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 }

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

25. 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 }

26. 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

27. 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;}

28. 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;}