Introduction to Computer Programming, Spring Term 2014 Practice Assignment 4 Discussion:

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1 German University in Cairo Media Engineering and Technology Prof. Dr. Slim Abdennadher Dr. Ahmed Gamal Introduction to Computer Programming, Spring Term 2014 Practice Assignment 4 Discussion: Exercise 4-1 Adder Write a program that adds up integers that the user enters. First the programs asks how many numbers will be added up. Then the program prompts the user for each number. Finally, it prints the sum. The output should be something like: How many integers will be added: 5 Enter integer 1: 3 Enter integer 2: 4 Enter integer 3: -4 Enter integer 4: -3 Enter integer 5: 7 The sum is 7 p u b l i c c l a s s Adding System. o u t. p r i n t l n ( "How many i n t e g e r s w i l l be added? " ) ; i n t n = sc. n e x t I n t ( ) ; i n t i, x, sum = 0 ; f o r ( i = 0 ; i <n ; i ++) System. o u t. p r i n t l n ( " E n t e r i n t e g e r " +( i + 1 ) ) ; x = sc. n e x t I n t ( ) sum += x ; System. o u t. p r i n t l n ( " The sum= "+sum ) ; 1

2 Exercise 4-2 Euclidean Algorithm The Euclidean algorithm determines the greatest common divisor (GCD) of two positive numbers by repeatedly replacing the larger number with the result of subtracting the smaller one from it until the two numbers are equal. Write a Java program for Euclidean algorithm where the user has to enter the two numbers and the program should calculate their greatest common divisor. The output should be something like: Please, enter a first number: 45 Please, enter a second number: 22 The GCD of 45 and 22 is 1 p u b l i c c l a s s E u c l i d i a n System. o u t. p r i n t l n ( " P l e a s e, e n t e r a number : " ) ; i n t num1 = sc. n e x t I n t ( ) ; System. o u t. p r i n t l n ( " P l e a s e, e n t e r a second number : " ) ; i n t num2 = sc. n e x t I n t ( ) ; i n t num1saved = num1 ; i n t num2saved = num2 ; while ( num1!= num2 ) i f ( num1 > num2 ) num1 = num2 ; e l s e num2 = num1 ; System. o u t. p r i n t l n ( " The GCD of " + num1saved + " and " + num2saved + " i s " + num1 ) ; Exercise 4-3 Caesar Cipher To be discussed in the tutorials Write a Java program which takes two input variables message of data type String and key of data type int. The program should shift each character in message with a distance of key. For example: if key=3 then a will be replaced by d and b will be replaced by e and so on. Hint: You can use the following method charat(int index): Returns the character at the specified index. The first character of the sequence is at index 0, the next at index 1 and so on. S t r i n g s = " H e l l o " ; char c = s. c h a r A t ( 0 ) ; The value of c is H. The output should be somthing like this: 2

3 Please enter the Message: Hat Please Enter the Key: 3 The encrypted word is: Kdw p u b l i c c l a s s C a e s a r System. o u t. p r i n t l n ( " P l e a s e E n t e r a Word t o be E n c r y p t e d : " ) ; S t r i n g s = sc. n e x t L i n e ( ) ; System. o u t. p r i n t l n ( " P l e a s e E n t e r a Key : " ) ; i n t key = sc. n e x t L i n e ( ) ; char x ; i n t l = s. l e n g t h ( ) ; i n t i = 0 ; i n t a s c i i = 0 ; while ( i < l ) a s c i i = s. c h a r A t ( i ) + key ; i f ( a s c i i > 122) a s c i i = 2 6 ; x = ( char ) a s c i i ; System. o u t. p r i n t ( x ) ; i ++; System. o u t. p r i n t ( " \ n " ) ; Exercise 4-4 String Manipulation To be discussed in the tutorials Write a program that determines the number of consonants, vowels, punctuation characters, and spaces in an input line. Read in the line into a String (in the usual way). Now use the charat() method in a loop to access the characters one by one. Use a switch statement to increment the appropriate variables based on the current character. After processing the line, print out the results. p u b l i c c l a s s Chars i n t c o n s o n a n t = 0, vowel = 0, p u n c t u a t i o n = 0, s p a c e = 0, d i g i t = 0 ; S t r i n g s t r, lowered ; System. o u t. p r i n t ( " E n t e r a s t r i n g : " ) ; 3

4 s t r = sc. n e x t L i n e ( ) ; / / Convert t h e l e t t e r o f t h e S t r i n g s t r t o lower case. lowered = s t r. tolowercase ( ) ; f o r ( i n t i = 0 ; i < lowered. l e n g t h ( ) ; i ++) s w i t c h ( lowered. c h a r A t ( i ) ) c ase : s p a c e ++; break ; c ase a : c ase e : c ase i : c ase o : c ase u : vowel ++; break ; c ase b : c ase c : c ase d : c ase f : c ase g : c ase h : c ase j : c ase k : c ase l : c ase m : c ase n : c ase p : c ase q : c ase r : c ase s : c ase t : c ase v : c ase w : c ase x : c ase y : c ase z : c o n s o n a n t ++; break ; c ase 0 : c ase 1 : c ase 2 : c ase 3 : c ase 4 : c ase 5 : c ase 6 : c ase 7 : c ase 8 : c ase 9 : d i g i t ++; break ; d e f a u l t : p u n c t u a t i o n ++; System. o u t. p r i n t l n ( " Number of c o n s o n a n t s : " + c o n s o n a n t ) ; System. o u t. p r i n t l n ( " Number of vowels : " + vowel ) ; System. o u t. p r i n t l n ( " Number of d i g i t s : " + d i g i t ) ; System. o u t. p r i n t l n ( " Number of p u n c t u a t i o n s : " + p u n c t u a t i o n ) ; System. o u t. p r i n t l n ( " Number of s p a c e s : " + s p a c e ) ; 4

5 Exercise 4-5 Fixed Length Write a program that asks the user to enter two words. The program then prints out both words on one line. The words will be separated by enought dots so that the total line length is 30. We can use it to make an index for a book. The user enters the name of the chapters/sections and the page number and the program generate the index. You can only print one dot at a time. Enter first word: Chapter 5 Enter second word: 153 Chapter p u b l i c c l a s s Word S t r i n g word1, word2, l i n e = " " ; i n t d o t s ; System. o u t. p r i n t ( " E n t e r f i r s t word : " ) ; word1 = sc. n e x t L i n e ( ) ; System. o u t. p r i n t ( " E n t e r second word : " ) ; word2 = sc. n e x t L i n e ( ) ; d o t s = 30 ( word1. l e n g t h ( ) + word2. l e n g t h ( ) ) ; l i n e = l i n e. c o n c a t ( word1 ) ; f o r ( i n t i = 0 ; i < d o t s ; i ++) l i n e = l i n e. c o n c a t ( ". " ) ; l i n e = l i n e. c o n c a t ( word2 ) ; System. o u t. p r i n t l n ( l i n e ) ; Exercise 4-6 Stream of Numbers Write a Java program to read a list of nonnegative integers and outputs the maximum integer, the minimum integer, and the average of all the integers. The end of the input is indicated by the user entering a negative number. Note that the negative number is not used in finding the maximum, minimum, or average. The output should be something like this: Please enter a sequence of positive numbers The maximum number is : 5 The minimum number is: 2 The average is: 3.5 Use in one program a while loop and in another program a do while loop. 5

6 Using While p u b l i c c l a s s NumbersWhile System. o u t. p r i n t l n ( " P l e a s e e n t e r t h e number " ) ; i n t num = sc. n e x t I n t ( ) ; i f ( num<0) System. o u t. p r i n t l n ( "No p o s i t i v e Numbers e n t e r e d " ) ; e l s e i n t small, l a r g e ; s m a l l = num ; l a r g e = num ; double sum = 0 ; double avg ; i n t c o u n t = 0 ; while ( num>=0) i f ( num< s m a l l ) s m a l l = um ; e l s e i f ( num> l a r g e ) l a r g e = num ; sum += num ; c o u n t ++; System. o u t. p r i n t l n ( " P l e a s e e n t e r a n o t h e r number : " ) ; num = sc. n e x t I n t ( ) ; avg = sum / c o u n t ; System. o u t. p r i n t l n ( " The a v e r a g e of t h e numbers i s " + avg ) ; System. o u t. p r i n t l n ( " The s m a l l e s t i n t e g e r you e n t e r e d i s " + s m a l l ) ; System. o u t. p r i n t l n ( " The l a r g e s t i n t e g e r you e n t e r e d i s " + l a r g e ) ; Using Do While c l a s s NumbersDoWhile System. o u t. p r i n t l n ( " P l e a s e E n t e r a s e q u e n c e of p o s i t i v e numbers : " ) ; i n t i ; / / G e t t i n g t h e f i r s t number and a s s i g n i n g i t t o min and max i = sc. n e x t I n t ( ) ; i n t max = i, min = i, sum = 0, c o u n t = 0 ; i f ( i <0) System. o u t. p r i n t l n ( "No p o s i t i v e numbers e n t e r e d " ) ; e l s e do 6

7 i f ( max< i ) max = i ; i f ( min> i ) min = i ; sum += i ; c o u n t ++; i = sc. n e x t I n t ( ) ; while ( i > 0 ) ; double avg = ( double ) sum / c o u n t ; System. o u t. p r i n t l n ( " The maximum number i s " + max ) ; System. o u t. p r i n t l n ( " The minimum number i s " + min ) ; System. o u t. p r i n t l n ( " The a v e r a g e i s " + avg ) ; Exercise 4-7 Triangle N Write a Java program to construct a triangle shape of numbers given that n is an input from the user. For example if n=6, the shape should look like the following: Solve using a single loop only. p u b l i c c l a s s T r i a n g l e System. o u t. p r i n t l n ( " P l e a s e e n t e r t h e number " ) ; i n t n = sc. n e x t I n t ( ) ; i n t i, j ; S t r i n g s = " " ; f o r ( i = 1 ; i <= n ; i ++) s += i ; System. o u t. p r i n t l n ( s ) ; Exercise 4-8 Pyramid To be discussed in the tutorials Construct the following pyramid of numbers given that n is an input from the user. For example if n=9, the pyramid 7

8 should look like the following: p u b l i c c l a s s TriangleNumbers S t r i n g l i n e ; System. o u t. p r i n t l n ( " P l e a s e e n t e r a number between 1 and 9 " ) ; i n t n = sc. n e x t I n t ( ) ; i n t i, m, j, z ; i f ( n / 2 < 5) f o r ( i = 1 ; i <= ( n / 2 ) + 1 ; i ++) f o r ( z = n i +1; z >0; z ) System. o u t. p r i n t ( " " ) ; f o r ( j = 1 ; j <= ( i 2 1); j ++) System. o u t. p r i n t ( j ) ; System. o u t. p r i n t l n ( ) ; e l s e System. o u t. p r i n t l n ( "You e n t e r e d a b i g number r a n g e " ) ; Exercise 4-9 Word Count Write a program that reads a sentence and a word from the user and finds the number of occurrences of the given word in the sentence. For example, the following could be a run of your program Enter the sentence: the students are enjoying life at the GUC Enter the word: the The sentence is "the students are enjoying life at the GUC". The word "the" occurs two times in the sentence p u b l i c c l a s s WordFinder 8

9 System. o u t. p r i n t l n ( " P l e a s e e n t e r t h e s e n t e n c e " ) ; S t r i n g l i n e = sc. n e x t L i n e ( ) ; System. o u t. p r i n t l n ( " P l e a s e e n t e r t h e key word " ) ; S t r i n g word = sc. n e x t L i n e ( ) ; i n t l i n e L e n g t h = l i n e. l e n g t h ( ) ; i n t wordlength = word. l e n g t h ( ) ; i n t wordcounter = 0 ; / / C o n s i d e r t h e. v a l u e v a r i a t i o n. In case t h e u s e r f o r g e t s i t. i f ( l i n e. c h a r A t ( l i n e L e n g t h 1)!=. ) l i n e = l i n e +. ; l i n e L e n g t h ++; i n t i = 0 ; i n t p o i n t e r = 0 ; char c ; S t r i n g tobecompared ; while ( i < l i n e L e n g t h 1) / / Get word by word do c = l i n e. c h a r A t ( p o i n t e r ) ; p o i n t e r ++; while ( ( c!= ) && ( c!= ; ) && ( c!=. ) && ( c!=, ) && ( p o i n t e r < l i n e L e n g t h ) ) ; / / s u b s t r i n g ( x, y ) r e t u r n s t h e word s t a r t i n g from x t o y 1 tobecompared = l i n e. s u b s t r i n g ( i, p o i n t e r 1); / / Now, compare o n l y i f t h e word l e n g t h e q u a l s t h e key word l e n g t h i f ( wordlength == tobecompared. l e n g t h ( ) ) / / Comparing t h e words i g n o r i n g Upper and Lower c a s e s i f ( word. e q u a l s I g n o r e C a s e ( tobecompared ) == true ) wordcounter ++; i = p o i n t e r ; System. o u t. p r i n t l n ( " Number of Occurence : " + wordcounter ) ; Exercise 4-10 Number of Digits Write a Java program that reads from the user positive integers and count the number of digits in them. The program should keep asking the user for entering integers until he/she enters -1. The output should be something like this: Please enter a number 524 Number of digits in 524 = 3 Please enter a number 24 9

10 Number of digits in 24 = 2 Please enter a number Number of digits in = 5 Please enter a number -1 Thank you! p u b l i c c l a s s D i g i t C o u n t e r System. o u t. p r i n t l n ( " P l e a s e e n t e r t h e f i r s t number " ) ; i n t num1 = sc. n e x t I n t ( ) ; i n t count, num2 ; while ( num1!= 1) c o u n t = 1 ; num2 = num1 ; while ( num2 / 1 0!= 0) num2 = num2 / 1 0 ; c o u n t ++; System. o u t. p r i n t l n ( " Number of d i g i t s i n " + num1 + " i s " + c o u n t ) ; System. o u t. p r i n t l n ( " P l e a s e e n t e r t h e n e x t number " ) ; num1 = sc. n e x t I n t ( ) ; Exercise 4-11 Divisors To be discussed in the lab Which integer between 1 and has the largest number of divisors, and how many divisors does it have? Write a program to find the answers and print out the results. It is possible that several integers in this range have the same, maximum number of divisors. Your program has to print out one of them. p u b l i c c l a s s M o s t D i v i s o r s i n t maxdivisors = 1 ; i n t numwithmax = 1 ; f o r ( i n t n = 2 ; n <= 10000; n ++) i n t d i v i s o r C o u n t = 0 ; f o r ( i n t d = 1 ; d <= n ; d ++) i f ( n % d == 0 ) d i v i s o r C o u n t ++; 10

11 i f ( d i v i s o r C o u n t > maxdivisors ) maxdivisors = d i v i s o r C o u n t ; numwithmax = n ; System. o u t. p r i n t l n ( "Among i n t e g e r s between 1 and 10000, " ) ; System. o u t. p r i n t l n ( " The max number of d i v i s o r s i s " + maxdivisors ) ; System. o u t. p r i n t l n ( "A num with " + maxdivisors + " d i v i s " + numwithmax ) ; Exercise 4-12 Extract Numbers To be discussed in the lab Write a Java program that takes a string containing text and nonnegative numbers form the user and prints out the numbers contained in the string in separate lines. Use nested loops. Running example Please enter your string The year has 365 days and the day has 12 hours Output The numbers contained in your string are p u b l i c c l a s s ExtractNumbers System. o u t. p r i n t l n ( " P l e a s e e n t e r your s t r i n g " ) ; S t r i n g s = sc. n e x t I n t ( ) ; i n t i = 0 ; i n t f l a g = 0 ; while ( i < s. l e n g t h ( ) ) / / t h e end o f t h e s t r i n g i s n o t reached and t h e r e i s a number between 0 and while ( i <s. l e n g t h ( ) && s. c harat ( i ) <=57 && s. c h arat ( i ) >=48 ) System. o u t. p r i n t ( s. c harat ( i ) ) ; i ++; f l a g ++; i f ( f l a g > 0) f l a g = 0 ; System. o u t. p r i n t l n ( ) ; i ++; 11

12 Exercise 4-13 Midterm Spring 2013 To be discussed in the tutorial The method Math.random() gives a real number between 0.0 and , and so 6*Math.random() is between 0.0 and The type-cast operator, (int), can be used to convert this to an integer: (int)(6*math.random()). Thus, (int)(6*math.random()) is one of the integers 0, 1, 2, 3, 4, and 5. To get a number between 1 and 6, we can add 1: (int)(6*math.random()) + 1 Using the statement above, we would like to know how many times we have to roll a pair of dice before they come up snake eyes? Note: Snake eyes means that both dice show a value of 1. Write a method that should return the number of rolls that it makes before the pair of dice come up snake eyes. The method should also display the following message, e.g.: It took 100 rolls to get snake eyes. Note: You have to use a do-while loop. i n t die1, d i e 2 ; / / The v a l u e s r o l l e d on t h e two d i c e. i n t c o u n t R o l l s ; / / Used t o c o u n t t h e number o f r o l l s. c o u n t R o l l s = 0 ; do d i e 1 = ( i n t ) ( Math. random ( ) 6 ) + 1 ; / / r o l l t h e d i c e d i e 2 = ( i n t ) ( Math. random ( ) 6 ) + 1 ; c o u n t R o l l s ++; / / and c o u n t t h i s r o l l while ( d i e 1!= 1 d i e 2!= 1 ) ; System. o u t. p r i n t l n ( " I t took " + c o u n t R o l l s + " r o l l s t o g e t snake eyes. " ) ; 12