CS111: PROGRAMMING LANGUAGE II

Transcription

1 1 CS111: PROGRAMMING LANGUAGE II Computer Science Department Lecture 1: Introduction

2 Lecture Contents 2 Course info Why programming?? Why Java?? Write once, run anywhere!! Java basics Input/output Variables Expressions Conditions Loops Methods Arrays

3 Course info 3 Website Book Course plan Assessment methods and grading Labs and practical assignments The term Project

4 Quiz!!!! 4 What is a program? (instructions) What is a programming language? (syntax/rules) What is a Software Package? (application domain)

5 Why Programming?? 5 Programming Enables you to make a computer do anything you want. First challenge. Learn a programming language. Next question. Which one?

6 Why Java?? 6 It s not about the language! Develop general programming skills applicable to many languages Javatar!!

7 Why Java? 7 Clarity - Keep it Simple Relatively easy graphics and GUI programming Lots of library packages Full documentation Colleges are teaching it Companies are using it Students want it Teachers welcome it... ;) Programmers drink it... :) Free compiler and IDEs

8 Java == class 8 Everything must be in a class. There are no global functions or global data. What about main??

9 Your first Java program.. 9

10 The Code life Cycle!! 10 Edit compile run

11 Write once, Compile Anywhere! 11

12 Your first Java program.. 12 // indicates a comment. class keyword Java is case sensitive braces {, } delimit a class body main Method Everything must be in a class There are no global functions or global data.

13 Basic language elements 13

14 Text I/O 14 Standard output. Flexible OS abstraction for output. In Java, applications use the standard output object (System.out) to display text on terminal.

15 Command line output 15 Multiple line O/P Formatting output public class TestIO { public static void main(string[] args) { System.out.println( Welcome to java ); System.out.println( Welcome to \n java ); System.out.print( Welcome to ); System.out.println( java ); System.out.printf( %s\n%s\n, Welcome to, java ); } } }

16 Common escape sequences 16

17 Printf Conversion-Characters 17

18 Strings & Text 18 String msg1 = new String( Hello ); String msg2 = Hello ; String msg3 = Year ; //valid??

19 Standard Input 19 input is received from Terminal window. Input entered while program is executing.

20 Reading values 20 use : import java.util.scanner; Define an object of the Scanner class: Scanner input = new Scanner(System.in); input values: num1 = input.nextint(); Display after calculation: System.out.printf( the square is : %d \n, num1*num1);

21 example 21

22 example 22

23 variables 23 Declaration, memory allocation, initialization data type variable name int total = 0; int count, temp, result; Multiple variables can be created in one declaration

24 Constants 24 A constant variable is an identifier that is similar to a variable except that it holds one value for its entire existence Why constants: give names to otherwise unclear literal values facilitate changes to the code prevent inadvertent errors In Java: final double PI = ;

25 Arithmetic Expressions 25 An expression is a combination of operators and operands Arithmetic expressions (we will see logical expressions later) are essentially special methods applied to numerical data objects: compute numeric results and make use of the arithmetic operators: Addition + Subtraction - Multiplication * Division / Remainder %

26 Assignment-related Operators 26 Increment and decrement operators: ++, -- Assignment operators: +=, -=, *=, /= these three expressions have the same effect count = count + 1; count += 1; count ++; these two expressions have the same effect count = count - 10; count -= 10;

27 Operator Precedence 27 What is the order of evaluation in the following expressions? a + b + c + d + e a + b * c - d / e a / (b + c) - d % e a / (b * (c + (d - e)))

28 How Do Data Conversions Happen? 28 Implicitly: occurs automatically uses widening conversion, Examples: 4.0 / 8 (which / is it: double/double, float/float, int/int) 4 / 8.0 (which / is it: double/double, float/float, int/int) / / 9 / 10.0 (what is the value?)

29 How Do Data Conversions Happen? 29 Explicitly: Casting widening / narrowing conversions Examples: double MyResult; MyResult = 12.0 / 5.0; //OK int myint = (int) MyResult; // truncation MyResult = (double)myint/3.0;

30 Be careful!! 30 Example: in 1996, Ariane 5 rocket exploded after takeoff because of bad type conversion.

31 Class Math 31 All Math class methods are static Each is called by preceding the name of the method with the class name Math and the dot (.) separator Method arguments may be constants, variables or expressions

32 32

33 Example 33 Solve quadratic equation ax 2 + bx + c = 0. public class Quadratic { public static void main(string[] args) { double a,b,c,d; // input coefficient values.. } } // calculate roots d = Math.sqrt(b*b - 4.0*a*c); double root1 = (-b + d) / (2.0*a); double root2 = (-b - d) / (2.0*a); // print them out System.out.println(root1); System.out.println(root2);

34 Lecture Contents 34 Java basics (part II)

35 Conditions & Branching 35

36 Conditional Statements 36 A conditional statement lets us choose which statement will be executed next Conditional statements give us the power to make basic decisions Java's conditional statements: the if and if-else statements the conditional operator the switch statement

37 The if Statement 37 The if statement has the following syntax: if is a Java reserved word The condition must be a boolean expression. e.g., a boolean variable, a == b, a <= b. It must evaluate to either true or false. if ( condition ) statement1; else statement2; If the condition is false, this statement is executed. If the condition is true, this statement is executed.

38 condition evaluated true false Statement 1 Statement 2 38 Logic of an if-else statement Several statements can be grouped together into a block statement A block is delimited by braces ( { } )

39 Relational operators 39

40 Logical Operators 40

41 Loops & Iterations 41

42 42 Loop Statements while statement while ( condition ) statement; do statement do { statement list; } while ( condition ); for statement for ( initialization ; condition ; increment ) statement;

43 43 While loops while ( condition ) statement;

44 Example 44 Look at the code and describe the output!! System.out.print( Enter a month (1 to 12): ); int month = scan.nextint(); while (month < 1 month > 12) { } System.out.println( month + is not a valid month. ); System.out.print( Enter a month (1 to 12): ); month = scan.nextint(); // set initial value of month so that the while condition // below is false initially int month = -1; while (month < 1 month > 12) { } System.out.print( Enter a month (1 to 12): ); month = scan.nextint();

45 45 do loops do { statement; } while ( condition );

46 Example 46 What is the difference here?? int month; // no need to initialize month do { System.out.print( Enter a month(1 to 12): ); month = scan.nextint(); } while (month < 1 month > 12); // beginning of the next statement

47 47 for loops for ( initialization ; condition ; increment ) statement;

48 Example 48 int sum = 0; for (int counter = 1; counter <= max; counter++) sum += counter; // beginning of the next statement Establish initial value of control variable. int counter = 1 Determine if final value of control variable has been reached. counter <= max false true sum+= counter Body of loop (this may be multiple statements) counter++ Incremen the control variable.

49 Methods 49 A method: groups a sequence of statement takes input, performs actions, and produces output In Java, each method is defined within specific class

50 Method Declaration: Header 50 A method declaration begins with a method header public class MyClass { static int min ( int num1, int num2 ) properties return type method name parameter list The parameter list specifies the type and name of each parameter The name of a parameter in the method declaration is called a formal argument

51 Method Declaration: Body 51 The header is followed by the method body: class MyClass { static int min(int num1, int num2) { int minvalue = num1 < num2? num1 : num2; return minvalue; } }

52 The return Statement 52 The return type of a method indicates the type of value that the method sends back to the calling location A method that does not return a value has a void return type The return statement specifies the value that will be returned Its expression must conform to the return type

53 Calling a Method 53 Each time a method is called, the values of the actual arguments in the invocation are assigned to the formal arguments int num = min(2, 3); static int min (int num1, int num2) { } int minvalue = (num1 < num2? num1 : num2); return minvalue;

54 54 Method Call Stack A method can call another method, who can call another method, main min(num1, num2, num3) println() min(1, 2, 3); println( )

55 What is an array? 55 Array data structures Group of variables (called elements) containing values of the same type. related data items of the same type. fixed length once created. Elements referred to using index or subscript. In java, Arrays are objects, so they re considered reference types. Every array object knows its own length and stores it in a length instance variable. Elements can be either primitive types or reference types (strings).

56 56 Array elements An index must be a nonnegative integer. Can use an expression as an index Every array object knows its own length and stores it in a length instance variable

57 7.3 Arrays in Java 57 declare create initialize int[] a; int a[]; a = new int[5]; for(int i=0;i<5;i++) a[i] = i*i;

58 Common Operations 58

59 59 That s all.. Welcome to the java world!!