Transcript Double
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. • 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 • To ask the user for an integer, we use: SavitchIn.readLineInt( ) • Example: int testScore = 0; System.out.println(“Enter test score: “); testScore = SavitchIn.readLineInt( ); • The SavitchIn command changes, depending on what kind of variable you are asking for – Int: – Double: – Char: SavitchIn.readLineInt( ) SavitchIn.readLineDouble( ) SavitchIn.readLineNonwhiteChar( ) (why nonWhite?? This way if the user types spaces -“white space” -- before whatever they type, Java ignores the spaces) – String: • Demo SavitchIn.readLine( ) 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 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. int x = 5; int y = 2; double z = x/y; what does z equal now? 2.0 int x = 5; double y = 2; double z = x/y; what does z equal now? 2.5 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. 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. Now 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. • 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. 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 Assignment • (InputNumbers) – Ask the user to enter 2 numbers. – Display the product, and quotient of the two numbers. – Display the first number, squared. – Display the second number, cubed. – Display the name of the drummer for the Canadian rock band Rush, followed by “rules.” – All of the results should look like the following, for example: “The sum of 6 and 7 is 13.” More Assignments Yay (files should be named with this format: P117num4) • 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; don’t worry about the decimal problem for now)