Passing Data into and out of Functions in Java

Making QR in Java Passing Data into and out of Functions

Functions are logically separated from the main program This is a good thing, because this separation prevents certain kinds of errors Sometimes, however, you want to send information into a function You might also want

a function to return some type of value The antsParamhtml page rewrites the Ants song in a way that takes advantage of function input and output: <script type = text/javascript > //<![CDATA[ //from antsParamhtml I m not providing a figure showing this program because it looks just like antsFunctionpy to the user That s one of the advantages of functions: You can improve the underlying behavior of a program without imposing a change in the user s experience Here s what the code looks like now: function chorus() { var text = and they all go marching down\n ; text += to the ground \n ; text += to get out \n ; text += of the rain \n ; text += \n ; text += boom boom boom boom boom boom boom boom \n ; return text; } // end chorus function verse(verseNum){ var distraction = ; if (verseNum == 1){ distraction = suck his thumb ; } else if (verseNum == 2){ distraction = tie his shoe ; } else { distraction = I have no idea ; } var text = The ants text += verseNum + hurrah \n ; text += The ants go text += verseNum + hurrah \n ; text += The ants go text += verseNum + text += the little text += distraction; return text; } // end verse1 //main code alert(verse(1)); alert(chorus()); alert(verse(2)); alert(chorus()); //]]> </script> go marching ; by + verseNum + hurrah, marching ; by + verseNum + hurrah, marching ; by + verseNum; one stops to ;

There are a couple of important new ideas in this code (keep in mind that this is just the overview specifics are coming in the next few sections): These functions return a value The functions don t do their own alert statements any more Instead, they create a value and return it to the main program There s only one verse function Because the verses are all pretty similar, it makes sense to have only one verse function This improved function needs to know what verse it s working on to handle the differences

The main code has been changed in one significant way In the last program, the main code called the functions, which did all the work This time, the functions don t actually do the output themselves Instead, they collect information and pass it back to the main program Inside the main code, each function is treated like a variable You ve seen this behavior before: The prompt() method returns a value Now the chorus() and verse() methods also return values You can do anything you want to this value, including printing it out or comparing it to some other value It s often considered a good idea to separate the creation of data from its use as I ve done here That way you have more flexibility After a function creates some information, you can print it to the screen, store it on a Web page, put it in a database, or whatever

The chorus has been changed to return a value Take another look at the chorus() function to see what I mean: function chorus() { var text = and they all go marching down\n ; text += to the ground \n ; text += to get out \n ; text += of the rain \n ; text += \n ; text += boom boom boom boom boom boom boom boom \n ; return text; } // end chorus