Lab 6 Using variables, Java expression evaluation with operations like +, -, *, %, / and order of operations Project 1. Using variables. Create a new Java project. Type the following lines (no need to...

Lab 6


Lab 6 Using variables, Java expression evaluation with operations like +, -, *, %, / and order of operations Project 1. Using variables. Create a new Java project. Type the following lines (no need to copy comments) in order as they appear, and answer questions from comments before moving further. Code intentionally is not perfect, and if you run it as is, you will see error messages. Based on your previous teamwork assignment (#4) and lecture form last week you should be able to figure out why these error messages appear. int minutes, seconds; double seconds = 100; // minutes = 75; System.out.println(minutes); //Now, uncomment line 3 with minutes = 75; /* Is your printing statement works now? So what was the error before? Note that this is a comment on multi-lines!*/ minutes = minutes+75; System.out.println(minutes+seconds); System.out.println(seconds); seconds = 500; System.out.println(seconds); System.out.println(“minutes = ” + minutes); /*check font for double quotes above, sometimes it gets mixed up so it is better to type your own quotes*/ Project 2. Two kinds of pluses in JAVA /* Plus sign marked in yellow is NOT regular algebraic plus. It does not make sense to sum up text (whatever appears in double quotes is text) and number, right? But it is useful for us to print some text and then immediately a number, this makes such number put into a context and more readable for users who do not see the code but only the output of the program they interact with. */ int hours = 2; int minutes = 25; int seconds = 55; System.out.println(“hours = ” + hours);//concatenation System.out.println(“minutes = ” + minutes);//concatenation System.out.println(“seconds = ” + seconds);//concatenation System.out.println(hours + minutes + seconds); //algebraic plus System.out.println(“total sum is: ” + (hours + minutes + seconds)); System.out.println(“total sum is: ” + hours + minutes + seconds)); Question: example above seem same as before except parenthesis. But the result is different! Why? Project 3. Evaluating expressions Java could be used as a calculator of sorts, but we need to be careful, as it does not always adhere to algebraic rules. You have already see what happens with plus! Java has more surprises for us! Predict what the following statements will print, then try it in JAVA. System.out.println(3+5); System.out.println(3+5.0); System.out.println(3*3); System.out.println(3.0*3.0); System.out.println(3/3); System.out.println(3/3.0); System.out.println(15.9/3); System.out.println(1.5/5); System.out.println(3/5); //careful! Integer division is special in JAVA System.out.println(5/3); //careful! Integer division is special in JAVA // next is remainder operation! System.out.println(3%2); System.out.println(2%3); System.out.println(3%3.0); System.out.println(0%3.0); // multiple operations! System.out.println(2 + 3%2); System.out.println(1 - 2%3); System.out.println(3 + 3*3.0); System.out.println(3 - 0%3.0); System.out.println(3 + 3*3%3.0); System.out.println(3 – 3/3%3.0); Question: which operations have higher order pf precedence? E.g. multiplication is “more important” than summation and should be done first. What about other operations? Project 4 (optional, have extra 20 credits). Advanced examples with pluses. Predict what will be printed as a result of execution of each of the following printing statements. Run each of these lines on its own (comment out others, or just type one by one). System.out.println(11 + "xyz" + 22); System.out.println(11 + 22 + " xyz " + 33); System.out.println("xyz " + 11+22); System.out.println(" xyz " + 11*22); System.out.println(" xyz " -11+22); Question: Figure out why your answers were not the same as JAVA answers. Check if it is consistent with rule you developed in previous Project. Update the rule if necessary (on how Java treats 2 kinds of pluses, how it can distinguish which is which). Project 5 (optional, have extra 20 credits). Advanced project on type compatibility. int x = 2.5; // Question: results in error. Why? double y = 2; // Question: not an error. Why? Try to print y value and see what happens!