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Other types of variables

Other types of variables. double (also known as “floating point number”) allows decimals much more useful than integers, but takes up more memory char A single character You must put the character in single quotes , if you are giving a char value in your code

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Other types of variables

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  1. Other types of variables • double (also known as “floating point number”) • allows decimals • much more useful than integers, but takes up more memory • char • A single character • You must put the character in single quotes, if you are giving a char value in your code example: char myGrade = ‘ ’; • String • Words, phrases, sentences • Capitalize String • Use double quotes example: String firstName= “”; • Demo

  2. Arithmetic • You can perform arithmetic with numbers and/or variables. • Java follows mathematical order of operations (PEMDAS). • Example: 4 + 36 / 2  this equals 22, not 20.

  3. We input data from whoever is using the program by using the SavitchIn class. • A class is another Java program (usually written by someone else) that you can use without having to rewrite it each time • The SavitchIn class must be in the same folder that your programs are in. • To ask the user for an integer, we use: variable = SavitchIn.readLineInt( ) • Example: inttestScore = 0; System.out.println(“Enter test score: “); testScore = SavitchIn.readLineInt( ); • Demo

  4. The SavitchIn command changes, depending on what kind of variable you are asking for • int: SavitchIn.readLineInt( ) • double: SavitchIn.readLineDouble( ) • char: SavitchIn.readLineNonwhiteChar( ) (why nonWhite?? This way if the user types spaces -- “white space” -- before whatever they type, Java ignores the spaces) • String: SavitchIn.readLine( ) • Demo

  5. Important: never use these: x = SavitchIn.readInt(); y = SavitchIn.readChar(); z = SavitchIn.readString();

  6. char ltr = ‘ ‘; ltr = ‘b’; System.out.println(ltr + ltr); What would this display?

  7. Type Casting • Let’s say you have a double that you need to convert into an integer • This can be accomplished by type casting: int x = 0; double y = 3.7; x = (int)y; // the (int) is where the type casting occurs • What does x equal now? also valid: x = (int)(y); incorrect: x = int(y);

  8. Integer vs. Double division • Guess the result of the following: int x = 5; int y = 2; int z = x/y; • Dividing with integers: the decimal part of the answer is truncated (erased). • To be accurate, use at least one double, or one decimal in your division.

  9. int x = 5; int y = 2; double z = x/y; what does z equal now? 2.0 ***It doesn’t matter that the “answer,” z, is a double. The sequence of how the code is executed is important here. Java does the division FIRST, then assigns the result to the variable z. ***Since 5/2 does equal 2, Java assigns 2 to the variable z.

  10. int x = 5; double y = 2; double z = x/y; what does z equal now? 2.5

  11. int x = 5; int y = 2; double z = (double)(x/y); what does z equal now? 2.0 why? because x/y = 2, then 2 is type-casted (converted) into a double.

  12. int x = 5; int y = 2; double z = (double)x/y; what does z equal now? 2.5 why? Notice the slight change in parentheses from the previous slide. First, x is type-casted from 5 to 5.0. Next, 5.0/2 = 2.5. Remember, as long as one of the two numbers being divided is a double, then the result is a double.

  13. Variables do not have to be used in order to work with doubles and integers. For example: System.out.println(9/4); (this would display 2) System.out.println(9.0/4); (this would display 2.25) System.out.println(9/4.0); (this would display 2.25) System.out.println(9.0/4.0); (this would display 2.25) Notice that as long as one of the two numbers being divided is a double, then the answer will be a double.

  14. Modulus Division • Using the modulus symbol, %, determines the remainder 10 % 6 = 4 13 % 5 = ? = 3 283 % 100 = ? = 83 26 % 2 = ? = 0 27 % 2 = ? = 1 (any even #) % 2 = ? = 0 (any odd #) % 2 = ? = 1 3 % 8 = 3

  15. Assignment #1 • (InputNumbers) • Ask the user to enter 2 numbers and 1 letter. • Display the letter 3 times on the same line, like this: “QQQ” • Display the sum, difference, product, and quotient of the two numbers. • Display the first number, squared. • Display the second number, cubed. • All of the results should look like the following, for example: “The sum of 6 and 8 is 14.”

  16. Assignments (files should be named using this format: P117num4, P117num5, etc) • P. 117-118: • #4 (Ignore “Create… application to”; look up formula online) • #5 (remember: “floating point value” is another name for a double) • #6 • #7 (hints: use both modulus division and integer division; how many seconds are in an hour?) • #11 (start by asking user for # of gallons used, starting odometer #, and ending odometer #) • #12 (ask the user how many of each coin)

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