CS Exam 1 Study Guide and Practice Exam

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1 CS Exam 1 Study Guide and Practice Exam September 11, 2017 Summary 1 Disclaimer 2 Variables 2.1 Primitive Types Suggestions, Warnings, and Resources FAQs Printing 3.1 FAQs Conditional Statements 4.1 if-else if-else Statements Difference between if-if-if and if-else if-else Switch Statements Suggestions, Warnings, and Resources Scanners 5.1 Suggestions, Warnings, and Resources FAQs Practice Written Exam 6.1 Short Answer Tracing Code Programming Quiz Practice Exam 8 Suggestions for Studying and Test Taking 8.1 Written Programming Quiz Common Errors Challenges Answers to Practice Written and Programming Problems 9.1 Written Short Answer Tracing Programming

2 1 Disclaimer This is a review of the material so far, but there may be material on the exam not covered in this study guide. 2 Variables 2.1 Primitive Types The eight primitive types are: int, double, char, float, long, short, byte, and boolean. So far you ve learned about two reference types, a String and a Scanner. These are NOT a primitive types, you will learn why later in the semester. Below are a few examples of declaring a variable. Format: type var name;. 1 i n t i ; 2 double d ; 3 char c ; 4 S t r i n g s ; Below are a few examples of assigning a variable. Format: var name = value;. 1 i = 3 ; 2 d = 4. 5 ; 3 c = a ; 4 s = Hey a l l! ; Below are a few examples of initializing a variable. Initializing is the combination of declaring and assigning. Format: type var name = value; 1 boolean b = t r u e ; 2 f l o a t f = F ; 3 long l = 32L ; 4 S t r i n g r e s p o n s e = Yes ; Remember: Every variable must always have a declaration (assignment can come later). Below are a few examples of typecasting. 1 i n t i = 3 ; 2 double d = ( double ) i ; 3 char c = c ; 4 i n t a s c i i c = ( i n t ) c ; Remember: If you typecast you can lose information, for example if I typecast 6.8 to an integer I will get back Suggestions, Warnings, and Resources Warning: Make sure you use the correct ticks/quotes for variables. For example, to assign/initialize a char you must use (ticks or single quotes), to assign/initialize a String you must use (double quotes), and numbers don t use ticks or quotes. 2.3 FAQs 1. Q: Why is there an F or L at the end of a long or float value? Is it case sensitive? A: If you leave off the F when assigning or initializing a float, Java will assume you want a double (instead of a float). A float can hold 32-bit number and a double can hold a 64-bit number. You only need to add an L when assigning/initializing a long when the value won t fit into an int. An int can hold numbers between 2 31 and and a long can hold numbers between 2 63 and The F and the L are not case sensitive, but be careful a lower case l looks an awful like the number 1.

3 3 Printing So far you know of two ways to print to the console: System.out.print();, System.out.println();. Below is an example of how and when you could use each. 1 i n t num1 = 3 ; 2 i n t num2 = 5 ; 3 i n t num3 = 9 ; 4 double avg = (num1 + num2 + num3) / 3 ; 5 6 // The f o l l o w i n g t h r e e p r i n t statements are e q u i v a l e n t 7 System. out. p r i n t ( Average + num1 +, + num2 +, and + num3 + : + avg + \n ) ; 8 System. out. p r i n t l n ( Average + num1 +, + num2 +, and + num3 + : + avg ) ; This outputs the following: Average 3, 5, and 9: 5.0 Average 3, 5, and 9: 5.0 System.out.print(); is the same as System.out.println(); except it doesn t have a new line character at the end of the line. 3.1 FAQs 1. Q: Can you use either print or println to print? Is there a specific time you d use one over the other? A: You can use either to print at any time, however, one might be easier in some situations over the other. 4 Conditional Statements 4.1 if-else if-else Statements 1 p u b l i c c l a s s C o n d i t i o n a l s { 2 p u b l i c s t a t i c void main ( S t r i n g [ ] a r g s ) { 3 i n t i = 0 ; 4 // i f statement 5 i f ( i == 0) { 6 System. out. p r i n t l n ( i == 0 ) ; 7 } 8 boolean b = t r u e ; 9 // I don t need b r a c k e t s because I only have one l i n e o f code 10 // under each statement. However, you can always have b r a c k e t s 11 // l i k e the example above. 12 i f ( b == f a l s e ) 13 System. out. p r i n t l n ( b i s FALSE ) ; 14 e l s e 15 System. out. p r i n t l n ( b i s TRUE ) ; i n t i 1 = 3 2 ; 18 // here I do need b r a c k e t s because t h e r e i s more than one 19 // l i n e o f code nested i n my i f statement. 20 i f ( i 1 >= 15) { 21 System. out. p r i n t l n ( i 1 i s g r e a t e r than or equal to 15 ) ; 22 i 1 ++; 23 } 24 e l s e i f ( i < 3) 25 System. out. p r i n t l n ( i i s l e s s than 3 ) ; 26 // e l s e s are l i k e catch a l l s t h e r e are a s e c t i o n o f numbers 27 // that aren t covered by my i f and e l s e i f so my e l s e w i l l 28 // handle t h o s e v a l u e s 29 e l s e 30 System. out. p r i n t l n ( i must be between 3 and 14 ) ; // sometimes you don t need an e l s e 33 S t r i n g name = Waldo ; 34 // i f I have found Waldo I want to say I found him but...

4 35 i f ( name. e q u a l s ( Waldo ) ) 36 System. out. p r i n t l n ( Found him! ) ; 37 // i f I didn t f i n d him I don t want to do anything 38 } 39 } The output from the above code is: i == 0 b is TRUE i1 is greater than or equal to 15 Found him! 4.2 Difference between if-if-if and if-else if-else If you use an if-else if-else statement and multiple conditionals are true, the program executes the first true conditional and then exits. If you use an if-if-if statement and multiple conditionals are true, the program will execute all of the true conditionals. 1 p u b l i c c l a s s C o n d i t i o n a l s { 2 p u b l i c s t a t i c void main ( S t r i n g [ ] a r g s ) { 3 i n t i = ; 4 System. out. p r i n t l n ( i f e l s e i f e l s e statement ) ; 5 i f ( i == 128) 6 System. out. p r i n t l n ( i == 128 ) ; 7 e l s e i f ( i > 100) 8 System. out. p r i n t l n ( i > 100 ) ; 9 e l s e i f ( i < 130) 10 System. out. p r i n t l n ( i < 130 ) ; System. out. p r i n t l n ( i f i f i f statement ) ; i f ( i == 128) 15 System. out. p r i n t l n ( i == 128 ) ; 16 i f ( i > 100) 17 System. out. p r i n t l n ( i > 100 ) ; 18 i f ( i < 130) 19 System. out. p r i n t l n ( I < 130 ) ; 20 } 21 } The output from the above code is: if-else if-else statement i == 128 if-if-if statement i == 128 i > 100 I < Switch Statements 1 p u b l i c c l a s s C o n d i t i o n a l s { 2 p u b l i c s t a t i c void main ( S t r i n g [ ] a r g s ) { 3 i n t i = 3 2 ; 4 switch ( i ) { 5 c a s e 1 0 : System. out. p r i n t l n ( i = 10 ) ; break ; 6 c a s e 3 2 : System. out. p r i n t l n ( i = 32 ) ; break ; 7 c a s e : System. out. p r i n t l n ( i = 101 ) ; break ; 8 d e f a u l t : System. out. p r i n t l n ( i i s not 10, 32, or 101 ) ; 9 } // beware o f your breaks! 12 char c = b ;

5 13 switch ( c ) { 14 c a s e a : System. out. p r i n t l n ( c = a ) ; 15 c a s e b : System. out. p r i n t l n ( c = b ) ; 16 c a s e c : System. out. p r i n t l n ( c = c ) ; 17 d e f a u l t : System. out. p r i n t l n ( c i s not a, b, or c ) ; 18 } // times you might want to not have breaks 21 i n t dogs = 0, c a t s = 0 ; 22 S t r i n g breed = German Shepard ; // s p a c i n g doesn t matter 25 // you aren t r e q u i r e d to have a d e f a u l t 26 // l i k e you aren t r e q u i r e d to have an e l s e 27 // j u s t be aware that t h e r e are p o s s i b l e c a s e s 28 // that aren t being handled. 29 switch ( breed ) { 30 c a s e Boxer : 31 c a s e Great Dane : 32 c a s e German Shepard : 33 c a s e Lab : 34 dogs++; break ; c a s e C a l i c o : c a s e B r i t i s h S h o r t h a i r : c a s e Siamese : 37 c a t s ++; break ; 38 } 39 System. out. p r i n t l n ( Dogs : + dogs +, Cats + c a t s ) ; 40 } 41 } The output from the above code is: i = 32 c = b c = c c is not a, b, or c Dogs: 1, Cats Suggestions, Warnings, and Resources Warning: Don t add a semicolon after your conditional. For example if (32 == 32);. Warning: Be aware of when you should and shouldn t have breaks in your switch statement. 5 Scanners Below is an example of reading from the keyboard/console. 1 // importing n e c e s s a r y methods 2 import java. u t i l. Scanner ; 3 4 p u b l i c c l a s s S c a n n e r P r a c t i c e { 5 p u b l i c s t a t i c void main ( S t r i n g [ ] a r g s ) { 6 // I n i t i a l i z e s a Scanner o b j e c t c a l l e d r e a d e r 7 Scanner r e a d e r = new Scanner ( System. i n ) ; 8 // Prompting u s e r f o r an i n t e g e r 9 System. out. p r i n t ( Enter your f a v o r i t e i n t e g e r : ) ; 10 // Read and s t o r e an i n t 11 i n t f a v o r i t e n u m b e r = r e a d e r. n e x t I n t ( ) ; 12 // Prompting u s e r f o r a decimal 13 System. out. p r i n t ( Enter your f a v o r i t e decimal number : ) ; 14 // Read and s t o r e a double 15 double f a v o r i t e d e c i m a l = r e a d e r. nextdouble ( ) ; 16 // p r i n t i n g summary 17 System. out. p r i n t l n ( Your f a v o r i t e i n t e g e r i s + f a v o r i t e n u m b e r + \nyour f a v o r i t e decimal number i s + f a v o r i t e d e c i m a l ) ; 18 r e a d e r. c l o s e ( ) ;

6 19 } 20 } On the console, it looks like this: Enter your favorite integer: 3 Enter your favorite decimal number: 3.14 Your favorite integer is 3 Your favorite decimal number is Suggestions, Warnings, and Resources Suggestion: Get in the habit of closing your Scanners Resource: Use Oracle s documentation for more methods and examples 5.2 FAQs 1. Q: My code still works even though I didn t close my Scanner object, why do you guys teach so you have to close it? A: We teach it so you close your Scanners so you get in the habit of closing objects (better coding practice and when we get to PrintWriters you must close your object).

7 6 Practice Written Exam 6.1 Short Answer 1. Declare an integer named i0. 2. Initialize a float named f to Initialize a Scanner to read from the keyboard, called read. 4. Assign i0 to an integer entered from the user. 5. Close the Scanner. 6. Name the eight primitive types. 7. What is 18 % 3? 8. Write a switch statement based off of the character variable c. If c is a print hi, if c is b print okay, if c is c print then, if c is d print bye, if it is not a, b, c, or d print fine then. 9. Write an if statement that does the same thing as question Declare a Scanner called scan. Read in one int and store it into the predefined int variable called my int. Close your scanner.

8 6.2 Tracing Code For each question below, write what is printed. 1 import java. u t i l. Scanner ; 2 3 p u b l i c c l a s s Tracing { 4 p u b l i c s t a t i c void main ( S t r i n g [ ] a r g s ) { 5 i n t i = 3 ; 6 double d = ( double ) i ; 7 // Question 1 8 System. out. p r i n t l n ( i + + d ) ; 9 10 Scanner keys = new Scanner ( System. i n ) ; 11 d = keys. n e x t I n t ( ) ; 12 i = ( i n t ) keys. nextdouble ( ) ; // Question 2 ( assume the u s e r e n t e r s 8 and r e s p e c t i v e l y ) 15 System. out. p r i n t l n ( i + + d ) ; S t r i n g r e s u l t = i n i t i a l r e s u l t ; i f ( d > 98) 20 r e s u l t = g r e a t e r than 98 ; 21 e l s e 22 r e s u l t = l e s s than or equal to 98 ; 23 System. out. p r i n t l n ( r e s u l t ) ; char grade = a ; 26 // Question 3 27 switch ( grade ) { 28 c a s e a : System. out. p r i n t l n ( Passing! ) ; 29 c a s e b : System. out. p r i n t l n ( Passing! ) ; 30 c a s e c : System. out. p r i n t l n ( Passing! ) ; 31 c a s e d : System. out. p r i n t l n ( Kinda s o r t a p a s s i n g ) ; 32 c a s e f : System. out. p r i n t l n ( Not r e a l l y p a s s i n g ) ; 33 d e f a u l t : System. out. p r i n t l n ( Not a grade l e t t e r r e c o g n i z e d ) ; 34 } 35 } 36 }

9 7 Programming Quiz Practice Exam 1. Create a class with a main method 2. Import the Scanner class 3. Create an int variable called age 4. Prompt the user to enter their age 5. Using the Scanner read in their age and assign the value to age 6. Write a conditional statement that prints the following under these conditions: if their age is 16 or older print You can drive! if their age is 18 or older print You can vote! if their age is 21 or older print You can drink! if their age is 25 or older print You can rent a car! 7. Close reader An example run would look like: Enter your age: 25 You can drive! You can vote! You can drink! You can rent a car! 8 Suggestions for Studying and Test Taking 8.1 Written When reading through code and writing the output: Write your variables on the side and as your variables change, you change your list on the side. Practice writing code in Eclipse and before you run your program guess what the output would be. is good practice for testing your own programs and also for the code tracing part of the exam. This If you need more tracing examples (or more coding examples in general), there is a Programs tab on the CS150 homepage. There are also examples on the Progress page. 8.2 Programming Quiz Go back to past recitations and assignments and redo them without using the INTERNET, friends, or past recitations/assignments. Practice writing code in Eclipse. Make up projects and problems or ask a TA and they can give you some challenges. Look at code, the more exposure you get to code (whether it s your own code or not) the easier it is to understand. Some sample code is under the Programs tab and the Progress Page. 8.3 Common Errors Incorrect brackets around conditional statements 8.4 Challenges CodingBat and Hackerrank offer good extra coding practice.

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11 9 Answers to Practice Written and Programming Problems 9.1 Written Short Answer 1. int i0; 2. float f = 4.0F; 3. Scanner read = new Scanner(System.in); 4. i0 = read.nextint(); 5. read.close(); 6. int, double, char, float, long, boolean, byte switch ( c ) { 2 c a s e a : System. out. p r i n t l n ( h i ) ; break ; 3 c a s e b : System. out. p r i n t l n ( okay ) ; break ; 4 c a s e c : System. out. p r i n t l n ( then ) ; break ; 5 c a s e d : System. out. p r i n t l n ( bye ) ; break ; 6 d e f a u l t : System. out. p r i n t l n ( f i n e then ) ; break ; 7 } 9.1 i f ( c == a ) 2 System. out. p r i n t l n ( h i ) ; 3 e l s e i f ( c == b ) 4 System. out. p r i n t l n ( okay ) ; 5 e l s e i f ( c == c ) 6 System. out. p r i n t l n ( then ) ; 7 e l s e i f ( c == d ) 8 System. out. p r i n t l n ( bye ) ; 9 e l s e 10 System. out. p r i n t l n ( f i n e then ) ; Scanner scan = new Scanner ( System. i n ) ; 2 my int = scan. n e x t I n t ( ) ; 3 scan. c l o s e ( ) ; Tracing less than or equal to Passing! Passing! Passing! Kinda sorta passing Not really passing Not a grade letter recognized

12 9.2 Programming NOTE: Your solution may be different from the code below, as long as your output matches my output (in all cases), you are answer is fine. 1 import java. u t i l. Scanner ; 2 3 p u b l i c c l a s s PracticeProgramming { 4 p u b l i c s t a t i c void main ( S t r i n g [ ] a r g s ) { 5 Scanner r e a d e r = new Scanner ( System. i n ) ; 6 i n t age ; 7 8 System. out. p r i n t ( Enter your age : ) ; 9 age = r e a d e r. n e x t I n t ( ) ; i f ( age >= 16) 12 System. out. p r i n t l n ( You can d r i v e! ) ; 13 i f ( age >= 18) 14 System. out. p r i n t l n ( You can vote! ) ; 15 i f ( age >= 21) 16 System. out. p r i n t l n ( You can drink! ) ; 17 i f ( age >= 25) 18 System. out. p r i n t l n ( You can r e n t a car! ) ; r e a d e r. c l o s e ( ) ; 21 } 22 }