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DIG 3134 Lecture 5: Functions Michael Moshell University of Central Florida

Media Software Design. DIG 3134 Lecture 5: Functions Michael Moshell University of Central Florida. The Objective: Learn what a function is, how to make one, and how to use it. What is a function? Think of it as a machine. You put in some inputs, and it does some work, and

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DIG 3134 Lecture 5: Functions Michael Moshell University of Central Florida

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  1. Media Software Design DIG 3134 Lecture 5: Functions Michael Moshell University of Central Florida

  2. The Objective: • Learn what a function is, • how to make one, • and how to use it.

  3. What is a function? Think of it as a machine. You put in some inputs, and it does some work, and produces some outputs. 4 square($n) 16 print "Four squared is".square(4); Four squared is 16

  4. How do you make a function You define it like this: function square($n) { $product=$n*$n; return $product; }

  5. How do you make a function You define it like this: function name function square($n) { $product=$n*$n; return $product; } // and then you "Call" it like this. $x=square(5); // or like this print square(6);

  6. How do you make a function You define it like this: function square($n) { $product=$n*$n; return $product; } // and then you "Call" it like this. $x=square(5); // or like this print square(6); input ("argument, or "parameter")

  7. How do you make a function You define it like this: function square($n) { $product=$n*$n; return $product; } // and then you "Call" it like this. $x=square(5); // or like this print square(6); output, or "return value"

  8. How do you make a function You define it like this: function square($n) { $value=$n*$n; return $value; } // and then you "Call" it like this. $x=square(5); // or like this print square(6); using the function

  9. How do you make a function You define it like this: function square($n) { $value=$n*$n; return $value; } // and then you "Call" it like this. $x=square(5); // or like this print square(6); $x is now 25 36

  10. Here's a fancier function. function makebox($height,$width) { $answer='<table>'; for ($row=1; $row<=$height;$row++) { $answer .='<tr>'; for ($col=1; $col<=$width; $col++) { $answer.='<td>*</td>'; } $answer .='</tr>'; } $answer .='</table>'; return $answer; } * * * * * * * * * * * * print makebox(3,4);

  11. Here's a fancier function. function makebox($height,$width) { $answer='<table>'; for ($row=1; $row<=$height;$row++) { $answer .='<tr>'; for ($col=1; $col<=$width; $col++) { $answer.='<td>*</td>'; } $answer .='</tr>'; } $answer .='</table>'; return $answer; } function name * * * * * * * * * * * * print makebox(3,4);

  12. Here's a fancier function. function makebox($height,$width) { $answer='<table>'; for ($row=1; $row<=$height;$row++) { $answer .='<tr>'; for ($col=1; $col<=$width; $col++) { $answer.='<td>*</td>'; } $answer .='</tr>'; } $answer .='</table>'; return $answer; } arguments, or parameters * * * * * * * * * * * * print makebox(3,4);

  13. Here's a fancier function. function makebox($height,$width) { $answer='<table>'; for ($row=1; $row<=$height;$row++) { $answer .='<tr>'; for ($col=1; $col<=$width; $col++) { $answer.='<td>*</td>'; } $answer .='</tr>'; } $answer .='</table>'; return $answer; } output value * * * * * * * * * * * * print makebox(3,4);

  14. Here's a fancier function. function makebox($height,$width) { $answer='<table>'; for ($row=1; $row<=$height;$row++) { $answer .='<tr>'; for ($col=1; $col<=$width; $col++) { $answer.='<td>*</td>'; } $answer .='</tr>'; } $answer .='</table>'; return $answer; } function declaration * * * * * * * * * * * * print makebox(3,4);

  15. Here's a fancier function. function makebox($height,$width) { $answer='<table>'; for ($row=1; $row<=$height;$row++) { $answer .='<tr>'; for ($col=1; $col<=$width; $col++) { $answer.='<td>*</td>'; } $answer .='</tr>'; } $answer .='</table>'; return $answer; } function Invocation ("call") * * * * * * * * * * * * print makebox(3,4);

  16. Returning a value function makebox($height,$width) { $answer='<table>'; for ($row=1; $row<=$height;$row++) { $answer .='<tr>'; for ($col=1; $col<=$width; $col++) { $answer.='<td>*</td>'; } $answer .='</tr>'; } $answer .='</table>'; return $answer; } Return statement * * * * * * * * * * * * print makebox(3,4);

  17. NOT Returning a value Not all functions have to return a value. Sometimes they just print their results... like this function printbold($text) { print "<strong>$text</strong>"; } print "I am "; printbold("Mike Moshell"); print " and you are not."; I am Mike Moshell and you are not.

  18. Function Exercise 1 Create a function called print3times($text), that prints three copies of the given text, each on a separate row. (Use the <br /> tag.) function print3times($text) { ? ? you design what goes in here. ? } print3times("Hooray no Ike!"); Do it now, before we reveal solution. Hooray no Ike! Hooray no Ike! Hooray no Ike!

  19. Function Exercise 1 Create a function called print3times($text), that produces three copies of the given text, each on a separate row. (Use the <br /> tag.) function print3times($text) { // the BFI ("brute force & ignorance") method: print $text.'<br />'; print $text.'<br />'; print $text.'<br />'; } print3times('Hooray no Ike!'); Hooray no Ike! Hooray no Ike! Hooray no Ike!

  20. Function Exercise 1 Create a function called print3times($text), that produces three copies of the given text, each on a separate row. (Use the <br /> tag.) function print3times($text) { // the elegant (extensible) method for ($i=1; $i<=3; $i++) { print $text.'<br />'; } } # print3times print3times('Hooray no Ike!'); Hooray no Ike! Hooray no Ike! Hooray no Ike!

  21. Function Exercise 2 Each person do one or 'tother.. NOW SIMPLE Create a function called polite($g,$name) where input $g will be 'm' or 'f' for male or female. It prints "Good morning Mr. Smith" or "Good morning, Ms. Smith" based on input like polite('m','Smith'). ADVANCED: In the fictional language Ispanglish, all female names end in 'a' and all male names end in 'e'. Produce a function called ispolite($name) that prints "Boonie Doozie, Madama Elena" for a female name like Elena, "Boonie Doozie, Maestro Mike' for a mail name like Mike.

  22. Function Exercise 2 SIMPLE Create a function called polite($g,$name) where input $g will be 'm' or 'f' for male or female. It prints "Good morning Mr. Smith." or "Good morning, Ms. Smith." based on input like this: polite('m','Smith'). That is, the parameter $g will have value 'm' or 'f'.

  23. Function Exercise 2 SIMPLE Create a function called polite($g,$name) where input $g will be 'm' or 'f' for male or female. It prints "Good morning Mr. Smith." or "Good morning, Ms. Smith." based on input like this: polite('m','Smith'). That is, the parameter $g will have value 'm' or 'f'. ((Don't look here if you want to figure it out for yourself!)) Hint->

  24. Function Exercise 2 SIMPLE Create a function called polite($g,$name) where input $g will be 'm' or 'f' for male or female. It prints "Good morning Mr. Smith." or "Good morning, Ms. Smith." based on input like this: polite('m','Smith'). That is, the parameter $g will have value 'm' or 'f'. function polite ($g, $name) { if (something) {print "Good morning Mr. $name";} else { print "Good morning Ms. $name." } } polite('m','Jones'); polite('f','Ramirez'); Hint-> Calls->

  25. Function Exercise 2 SIMPLE Create a function called polite($g,$name) where input $g will be 'm' or 'f' for male or female. It prints "Good morning Mr. Smith, or Ms. Smith.", based on input like polite('m','Smith'). Basic Solution function polite($g,$name) { if ($g=='m') { print "Good morning Mr. $name";} else { print "Good morning Ms. $name";} }

  26. Function Exercise 2 SIMPLE Create a function called polite($g,$name) where input $g will be 'm' or 'f' for male or female. It prints "Good morning Mr. Smith, or Ms. Smith.", based on input like polite('m','Smith'). Better Solution function polite($g,$name) { if ($g=='m') { print "Good morning Mr. $name";} else if ($g == 'f') { print "Good morning Ms. $name";} else { print "error 001: unknown gender selector $g.";} } - covers all cases - numbered error msgs - specific feedback on type of error (could be better)

  27. Function Exercise 2 ADVANCED: In the fictional language Ispanglish, all female names end in 'a' and all male names end in 'e'. Produce a function called ispolite($name) that prints "Boonie Doozie, Madama Elena" for a female name like Elena, "Boonie Doozie, Maestro Mike' for a mail name like Mike. -- Advanced students: Work on this problem for homework – You can check your work against my solution, on the last slide of this Powerpoint document.

  28. The Scope of Variables Variables created inside a function cannot be seen outside that function. Variables created outside a function cannot be seen inside that function. first pass: check syntax, $x=3; function monster( ) { print "inside first x=$x"; $x=5; print " second inside x=$x"; } monster( ); print "outside x=$x"; declare function 'monster'

  29. The Scope of Variables Variables created inside a function cannot be seen outside that function. Variables created outside a function cannot be seen inside that function. second pass:execute code. $x=3; function monster( ) { print "inside first x=$x"; $x=5; print " second inside x=$x"; } monster( ); print "outside x=$x"; outside x::3 variable x is created in global namespace

  30. The Scope of Variables Variables created inside a function cannot be seen outside that function. Variables created outside a function cannot be seen inside that function. $x=3; function monster( ) { print "inside first x=$x"; $x=5; print " second inside x=$x"; } monster( ); print "outside x=$x"; x::3 invoking 'monster'

  31. The Scope of Variables Variables created inside a function cannot be seen outside that function. Variables created outside a function cannot be seen inside that function. $x=3; function monster( ) { print “first inside x=$x”; $x=5; print " second inside x=$x"; } monster( ); print "outside x=$x"; x::3 first inside x= invoking 'monster'

  32. The Scope of Variables Variables created inside a function cannot be seen outside that function. Variables created outside a function cannot be seen inside that function. $x=3; function monster( ) { print "inside first x=$x"; $x=5; print " second inside x=$x"; } monster( ); print "outside x=$x"; x::3 first inside x= x::5 another x is created inside the function invoking 'monster'

  33. The Scope of Variables Variables created inside a function cannot be seen outside that function. Variables created outside a function cannot be seen inside that function. $x=3; function monster( ) { print "inside first x=$x"; $x=5; print " second inside x=$x"; } monster( ); print "outside x=$x"; x::3 first inside x= second inside x=5 x::5 invoking 'monster'

  34. The Scope of Variables Variables created inside a function cannot be seen outside that function. Variables created outside a function cannot be seen inside that function. $x=3; function monster( ) { print "inside first x=$x"; $x=5; print " second inside x=$x"; } monster( ); print "outside x=$x"; x::3 first inside x= second inside x=5 outside x=3

  35. The Global Declaration If you declare a variable 'global', the function uses the variable from the outside world. $x=3; function monster( ) { global $x; print "inside first x=$x"; $x=5; print " second inside x=$x"; } monster( ); print "outside x=$x"; x::3

  36. The Global Declaration If you declare a variable 'global', the function uses the variable from the outside world. $x=3; function monster( ) { global $x; print "inside first x=$x"; $x=5; print " second inside x=$x"; } monster( ); print "outside x=$x"; x::3 first inside x=3

  37. The Global Declaration If you declare a variable 'global', the function uses the variable from the outside world. $x=3; function monster( ) { global $x; print "inside first x=$x"; $x=5; print " second inside x=$x"; } monster( ); print "outside x=$x"; x::5 first inside x=3

  38. The Global Declaration If you declare a variable 'global', the function uses the variable from the outside world. $x=3; function monster( ) { global $x; print "inside first x=$x"; $x=5; print " second inside x=$x"; } monster( ); print "outside x=$x"; x::5 first inside x=3 second inside x=5

  39. The Global Declaration If you declare a variable 'global', the function uses the variable from the outside world. $x=3; function monster( ) { global $x; print "inside first x=$x"; $x=5; print " second inside x=$x"; } monster( ); print "outside x=$x"; x::5 first inside x=3 second inside x=5 outside x=5

  40. A parameter can be an array Consider this example: $invoice[0]=24.95; $invoice[1]=188.40; $invoice[2]=33.22; ... Here's a function to compute the total of the invoices. function total($n,$list) { $sum=0; for ($i=0; $i<$n; $i++) { $sum=$sum+$list[$i]; } return $sum; } print “Total charge:”. total(3,$invoice);

  41. Advanced topic: The Foreach command Consider this example: $partypeople[0]="Maria"; $partypeople[1]="Alfonso"; $partypeople[2]="Santa Claus"; $partypeople[3]="Billy"; ... but maybe we don't KNOW how many people are in the list. (It was created somewhere else in the code.) So we just need to have a way to say "For ALL the list's elements.."

  42. Advanced topic: The Foreach command Consider this example: function hasFred($list) { foreach ($list as $value) // no key needed this time { if ($value= = 'Fred') { return 1;} } // if you got here, no Fred was found return 0; } if (hasFred($partypeople)) { print "Yay, Fred will come!"; } else { print "Boo hoo, Fred won't come to our party!"; }

  43. Function Homework Design and program these functions for next week 1. function punchfred($who) If the parameter value is 'Fred' it prints out "I punch you in the mouf, Fred." If any other name (like Suzie), it prints out "A very good morning to you, Suzie!" 2. function maxtwo($x,$y) It returns the value of the larger of its two inputs. 3. function maxlist($list, $length) It returns the largest value in an array ($list) whose cells are numbered 0, 1, .... ($length-1).

  44. An Answer to Function Exercise 2 ADVANCED: In the fictional language Ispanglish, all female names end in 'a' and all male names end in 'e'. Produce a function called ispolite($name) that prints "Boonie Doozie, Madama Elena" for a female name like Elena, "Boonie Doozie, Maestro Mike' for a mail name like Mike. Spoiler Alert: Do not view the next slide unless you want to examine an answer to the Ispanglish exercise above.

  45. An Answer to Function Exercise 2 ADVANCED: In the fictional language Ispanglish, all female names end in 'a' and all male names end in 'e'. Produce a function called ispolite($name) that prints "Boonie Doozie, Madama Elena" for a female name like Elena, "Boonie Doozie, Maestro Mike' for a mail name like Mike. function ispolite($name) { $len=strlen($name); $last=substr($name,$len-1,1); if ($last = = 'a') { print "Boonie Doozie, Madama $name"; } else { print "Boonie Doozie, Maestro $name"; } } // It SHOULD include an error case ... no space here!

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