COMP 14 switch Developing Programs June 2 2000 Nick Vallidis Announcements P3 due Tuesday June 6 Review How does the do loop work do statement while condition How does the for loop work for initialization condition increment statement Review cont What are the 4 ways to decrement a variable What s the difference between i and i Today the switch statement Steps to take in developing a program switch The switch statement format switch expression case exp1 statement1 break case exp2 statement2 break default statement switch The switch statement format switch expression case exp1 statement1 Java break case exp2 reserved statement2 words break default statement switch The switch statement format switch expression case exp1 statement1 break case exp2 statement2 break default statement The expression is evaluated and control jumps to the case whose value matches If there is no matching case then control goes to default switch The switch statement format switch expression case exp1 statement1 break case exp2 statement2 break default statement The statements are executed starting from the corresponding case until it gets to a break At a break control jumps to the end of the switch switch The switch statement format switch expression case exp1 statement1 case exp2 statement2 break default statement But the break statements are optional so you could just run on to the next case if you leave it out switch example i is a character the user typed in switch i case a case A System out println You entered case Z System out println You entered default System out println You entered something other than 0 or 0 1 1 comments on switch only works with integral types any primitive type except boolean or the floating point types This is basically an equality test Developing programs The book describes for basic steps establishing the requirements creating a design implementing the code testing the implementation Developing programs For the small code fragments we ve done in class we ve gone straight for the implementation For the rest of your assignments it will really help you to go through this process Example assignment P2 We ll use assignment P2 Establishing requirements Here are the requirements read in two names greet the users read in the day of the month that each of the people was born report winner as person born earlier in month if it s a tie report that it s a tie Anything else Creating a design We ll start by breaking it down into manageable steps 1 ask for players names 1 5 greet users 2 ask for players days of birth 3 determine winner or that it s a tie 4 print out result Creating a design Then we can either break things down again if they re still big tasks or get down to writing specifics This is simple enough that we ll go to specifics next Exciting new term pseudocode a mixture of programming statements and English Example if class is over everyone can leave else everyone stays 1 ask for names prompt for first name read in first name prompt for second name read in second name 2 ask for day of birth ask first name for day of birth read in day of birth ask second name for day of birth read in day of birth 3 determine winner if days of birth are equal it s a tie else if person 1 s day person 2 s day person 1 was born first else person 2 was born first 4 print out result Turns out that it s easier to combine 3 4 if days of birth are equal print it s a tie else if person 1 s day person 2 s day print person 1 was born first else print person 2 was born first Now turn this into code The pseudocode should be written such that turning it into code is trivial Your turn Try this with the PB J example Let s talk about the requirements together first PB J requirements what you have robot w 2 arms jar of PB jar of J 2 slices of bread 1 knife what you have to do make PB J sandwich robot can only take simple instructions Now break down the task Aim for a maximum of about 7 steps at any one level So now we have 1 level Now break down each of these tasks into their steps Repeat this until you get down to steps you know how to program A well known algorithm Maybe you ve seen this before Lather Rinse Repeat What s wrong with this as an algorithm Assignment P3 Here s the order you should probably try to do things Get the framework going announcing the game asking name etc make the higher lower game work once don t worry about checking for valid input add the do you want to play again loop add checking for valid input do the extra credit Opening existing projects Some people have had trouble with getting their programs to run after they quit Visual J 2 of the ways to do this if it s your machine go to the File menu and right above exit will be the names of recent projects click on my computer and keep going through folders till you get to the right one and doubleclick on project name sln Homework read 4 1 4 2 and 3 3 3 5 if you missed that P3 is due Tuesday start now