CPSC Introduction to Computer Science for Computer Science Majors II Monir Zaman (Md Moniruzzaman)

Transcription

1 CPSC Introduction to Computer Science for Computer Science Majors II Monir Zaman (Md Moniruzzaman)

2 Tip: Error Messages Bug: A mistake in a program The process of eliminating bugs is called debugging Syntax error: A grammatical mistake in a program The compiler can detect these errors, and will output an error message saying what it thinks the error is, and where it thinks the error is 1-2 Copyright 2012 Pearson Addison-Wesley. All rights reserved.

3 Compute and output the result: int i=0,sum=0; while(++i<5){ sum=sum+i; //System.out.println(i); } System.out.println(sum);

4 Compute and output the result: int i=0,sum=0; while(i++<5){ sum=sum+i; //System.out.println(i); } System.out.println(sum);

5 Tip: Error Messages Run-time error: An error that is not detected until a program is run The compiler cannot detect these errors: an error message is not generated after compilation, but after execution Logic error: A mistake in the underlying algorithm for a program The compiler cannot detect these errors, and no error message is generated after compilation or execution, but the program does not do what it is supposed to do 1-5 Copyright 2012 Pearson Addison-Wesley. All rights reserved.

6 Print all the elements of an array int[] ar={23,45,67}; int i=0; while(i<4){ System.out.println(ar[i]); i++; }

7 Print all the elements of an array int[] ar={23,45,67}; int i=0; while(i<ar.length){ System.out.println(ar[i]); i++; }

8 int num=45; if(num>20){ if(num<10){ num*=10; } }

9 Class String Store text String name= John ; String name=null; String name;

10 String String name= John ; name.equals( smith ) Returns a boolean value: true/false

11 String name= John ; If( name.equals( smith ) ) { } System.out.printf( Names %s and %s are equal, name, smith );

12 String String name= John ; name.equalsignorecase( john ) Returns a boolean value: true

13 Method definition boolean equals (String) boolean equalsignorecase (String)

14 String touppercase() String tolowercase()

15 String touppercase() String tolowercase() Example: String a_b= stat101 ; System.out.println(a_b.toUpperCase()); STAT101

16 Some Methods in the Class String (Part 3 of 8) 1-16 Copyright 2012 Pearson Addison-Wesley. All rights reserved.

17 Some Methods in the Class String (Part 4 of 8) 1-17 Copyright 2012 Pearson Addison-Wesley. All rights reserved.

18 Some Methods in the Class String (Part 5 of 8) 1-18 Copyright 2012 Pearson Addison-Wesley. All rights reserved.

19 File Input import java.util.scanner; import java.io.fileinputstream; import java.io.filenotfoundexception; public class tryfileio{ public static void main(string[] args){ //this is comment try{ FileInputStream fis=new FileInputStream("/home/grads/mmoniruz/temp.txt"); Scanner fin=new Scanner(fis); System.out.printf("%s%n",fin.nextLine()); }//end of try catch(filenotfoundexception e){ System.out.println( Error message "+e); System.exit(0); }//end of catch }//end of main }//end of class

20 File Input import java.util.scanner; import java.io.fileinputstream; import java.io.filenotfoundexception; public class tryfileio{ public static void main(string[] args){ try{ FileInputStream fis=new FileInputStream("/home/grads/mmoniruz/temp.txt"); Scanner fin=new Scanner(fis); while(fin.hasnextline()){ System.out.printf("%s%n",fin.nextLine()); } }//end of try catch(filenotfoundexception e){ System.out.println( Error message "+e); System.exit(0); }//end of catch }//end of main }//end of class

21 Some Methods in the Class String (Part 6 of 8) 1-21 Copyright 2012 Pearson Addison-Wesley. All rights reserved.

22 Some Methods in the Class String (Part 7 of 8) 1-22 Copyright 2012 Pearson Addison-Wesley. All rights reserved.

23 Some Methods in the Class String (Part 7 of 8) String name= JOHN ; name.compareto( john ) returns a negative number 1-23 Copyright 2012 Pearson Addison-Wesley. All rights reserved.

24 Some Methods in the Class String (Part 8 of 8) 1-24 Copyright 2012 Pearson Addison-Wesley. All rights reserved.

25 Exercise Write a program that starts with a line of text and then outputs that line with the first occurrence of hate changed to love. A sample output of the program: The line of text to be changed is: I hate strong wind. I have rephrased that line to read: I love strong wind. Use a defined constant to store the line of text. You can have the word hate more than once in the line but change only its first occurrence.

26 Exercise II Create a text file containing the text I hate strong wind. Write a program that reads the text from the file and changes the first occurrence of hate to love. A sample output of the program: The line of text to be changed is: I hate strong wind. I have rephrased that line to read: I love strong wind. You can have the word hate more than once in the line but change only its first occurrence.