From Bing.com on Nov

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1 Functions

2 From Bing.com on Nov

3 We re going to look at some common patterns / algorithms for using an array The idea is that you first understand these Then you can apply them elsewhere And modify them to suit 3

4 Arrays Patterns: 1 Item At A Time 4

5 Some array problems can be solved by considering each item, one by one, without thinking about the rest of the array Examples: Print each item Find a particular item in the array (or determine that it's not present) This uses the 'iterate through the array pattern Let s start with an overview of what each line of code is supposed to do 5

6 Here's what the 'main' / on click handler looks like for the FindInArray logic: $("#findinarray").click( function() { (1) var cars = ["Saab", "Volvo", "BMW"]; () var target = $("#findtarget").val(); // Now convert the array to being a string so we can print it out onto the page: for (i in cars) { if( cars[i] == target) { $("#findoutput").html( "Found " + target + " at array slot " + i ); return; // stop searching, otherwise we'll print the 'not found' message // after the loop $("#findoutput").html( "Did NOT find " + target + " in the array"); Start by defining an array (1), then get the string the user wants to search for (). 6

7 Here's what the 'main' / on click handler looks like for the FindInArray logic: $("#findinarray").click( function() { var cars = ["Saab", "Volvo", "BMW"]; var target = $("#findtarget").val(); // Now convert the array to being a string so we can print it out onto the page: (1) for (i in cars) { () if( cars[i] == target) { (3) $("#findoutput").html( "Found " + target + " at array slot " + i ); (4) return; // stop searching, otherwise we'll print the 'not found' message // after the loop $("#findoutput").html( "Did NOT find " + target + " in the array"); (1) The for loop walks through all the indeces in the array (0, 1, ) () If the current slot is the one that we re looking for (3) Display a message on the page (4) And then stop 7

8 Here's what the 'main' / on click handler looks like for the FindInArray logic: $("#findinarray").click( function() { var cars = ["Saab", "Volvo", "BMW"]; var target = $("#findtarget").val(); // Now convert the array to being a string so we can print it out onto the page: for (i in cars) { if( cars[i] == target) { $("#findoutput").html( "Found " + target + " at array slot " + i ); return; // stop searching, otherwise we'll print the 'not found' message // after the loop (1) $("#findoutput").html( "Did NOT find " + target + " in the array"); (1) If none of the elements match then we ll end up here 8

9 9 absent

10 Here's what the 'main' / on click handler looks like for the FindInArray logic: $("#findinarray").click( function() { var cars = ["Saab", "Volvo", "BMW"]; (1) var target = $("#findtarget").val(); () // Now convert the array to being a string so we can print it out onto the page: for (i in cars) { if( cars[i] == target) { cars[i] Saab $("#findoutput").html( "Found " + target + " at array slot " + i ); return; // stop searching, otherwise we'll print the 'not found' message $("#findoutput").html( "Did NOT find " + target + " in the array"); Done Current Future 0 1 Saab Volvo BMW i 0 target absent 10

11 Here's what the 'main' / on click handler looks like for the FindInArray logic: $("#findinarray").click( function() { var cars = ["Saab", "Volvo", "BMW"]; (1) var target = $("#findtarget").val(); () // Now convert the array to being a string so we can print it out onto the page: for (i in cars) { if( cars[i] == target) { cars[i] Volvo $("#findoutput").html( "Found " + target + " at array slot " + i ); return; // stop searching, otherwise we'll print the 'not found' message $("#findoutput").html( "Did NOT find " + target + " in the array"); Done Current 0 1 Saab Volvo BMW i 1 target Future absent 11

Here's what the 'main' / on click handler looks like for the FindInArray logic: $("#findinarray").click( function() { var cars = ["Saab", "Volvo", "BMW"]; (1) var target = $("#findtarget").

12 Here's what the 'main' / on click handler looks like for the FindInArray logic: $("#findinarray").click( function() { var cars = ["Saab", "Volvo", "BMW"]; (1) var target = $("#findtarget").val(); () // Now convert the array to being a string so we can print it out onto the page: for (i in cars) { if( cars[i] == target) { cars[i] BMW $("#findoutput").html( "Found " + target + " at array slot " + i ); return; // stop searching, otherwise we'll print the 'not found' message $("#findoutput").html( "Did NOT find " + target + " in the array"); Done Current 0 1 Saab Volvo BMW i target absent Future 1

13 Here's what the 'main' / on click handler looks like for the FindInArray logic: $("#findinarray").click( function() { var cars = ["Saab", "Volvo", "BMW"]; (1) var target = $("#findtarget").val(); () // Now convert the array to being a string so we can print it out onto the page: for (i in cars) { if( cars[i] == target) { cars[i] - $("#findoutput").html( "Found " + target + " at array slot " + i ); return; // stop searching, otherwise we'll print the 'not found' message $("#findoutput").html( "Did NOT find " + target + " in the array"); Done 0 1 Saab Volvo BMW i - target absent 13

14 14 present

15 Here's what the 'main' / on click handler looks like for the FindInArray logic: $("#findinarray").click( function() { var cars = ["Saab", "Volvo", "BMW"]; (1) var target = $("#findtarget").val(); () // Now convert the array to being a string so we can print it out onto the page: for (i in cars) { if( cars[i] == target) { cars[i] Saab $("#findoutput").html( "Found " + target + " at array slot " + i ); return; // stop searching, otherwise we'll print the 'not found' message $("#findoutput").html( "Did NOT find " + target + " in the array"); Done Current Future 0 1 Saab Volvo BMW i 0 target Volvo 15

16 Here's what the 'main' / on click handler looks like for the FindInArray logic: $("#findinarray").click( function() { var cars = ["Saab", "Volvo", "BMW"]; (1) var target = $("#findtarget").val(); () // Now convert the array to being a string so we can print it out onto the page: for (i in cars) { if( cars[i] == target) { cars[i] Volvo $("#findoutput").html( "Found " + target + " at array slot " + i ); return; // stop searching, otherwise we'll print the 'not found' message $("#findoutput").html( "Did NOT find " + target + " in the array"); Done Current 0 1 Saab Volvo BMW i 1 target Future Volvo 16

17 ICE #1: Parsons problems: Finding something in an array ICE #: Use this pattern to write new code printing everything in an array that matches a given criteria 17

18 Some array problems need to consider all the elements of the array, even though we see each one individually Examples: Find min/max calculate average concatenating / joining Difference in approach is that we retain, or persist, a value through multiple iterations of our loop. 18

19 Here's what the 'main' / on click handler looks like for the FindInArray logic: $("#findminimum").click( function() { (1) var nums = [10, 0,, -4, -, 4] () var minimumidx = 0; (3) var minimumval = nums[0]; // check each element of the array to see if it's what we're looking for for (i in nums) { if( nums[i] < minimumval) { minimumidx = i; minimumval = nums[i]; $("#findminimumoutput").html( "Smallest value is " + nums[minimumidx]+ " (located at slot " + minimumidx + " in the array)"); Start by defining an array (1) We re going to look at the very first element first. Having only looked at the first element that means it must be the smallest that we ve seen so far. We re going to remember the smallest that we ve seen so far is at index 1 () We re going to remember the smallest value that we ve seen so far (3) 19

20 Here's what the 'main' / on click handler looks like for the FindInArray logic: $("#findminimum").click( function() { var nums = [10, 0,, -4, -, 4] var minimumidx = 0; var minimumval = nums[0]; // check each element of the array to see if it's what we're looking for (1) for (i in nums) { () if( nums[i] < minimumval) { (3) minimumidx = i; (4) minimumval = nums[i]; $("#findminimumoutput").html( "Smallest value is " + nums[minimumidx]+ " (located at slot " + minimumidx + " in the array)"); (1) We ll go through every slot in the array () If the slot we re currently looking at is less than the smallest value that we ve seen so far (3) Then remember this index (4) And remember this value, which is now the NEW smallest value that we ve seen so far 0

21 Here's what the 'main' / on click handler looks like for the FindInArray logic: $("#findminimum").click( function() { var nums = [10, 0,, -4, -, 4] var minimumidx = 0; var minimumval = nums[0]; // check each element of the array to see if it's what we're looking for for (i in nums) { if( nums[i] < minimumval) { minimumidx = i; minimumval = nums[i]; (1) $("#findminimumoutput").html( "Smallest value is " + nums[minimumidx]+ " (located at slot " + minimumidx + " in the array)"); (1) Lastly, display the output on the page 1

23 Here's what the 'main' / on click handler looks like for the findminimum logic: $("#findminimum").click( function() { var nums = [10, 0,, -4, -] var minimumidx = 0; minimumidx 0 var minimumval = nums[0]; for (i in nums) { if( nums[i] < minimumval) { minimumval 10 minimumidx = i; minimumval = nums[i]; i 0 $("#findminimumoutput").html( "Smallest value is " + nums[minimumidx]+ " (located at slot " + minimumidx + " in the array)"); D o n e Current Future 4-3

24 Here's what the 'main' / on click handler looks like for the findminimum logic: $("#findminimum").click( function() { var nums = [10, 0,, -4, -] var minimumidx = 0; minimumidx 0 var minimumval = nums[0]; for (i in nums) { if( nums[i] < minimumval) { minimumval 10 minimumidx = i; minimumval = nums[i]; i 0 $("#findminimumoutput").html( "Smallest value is " + nums[minimumidx]+ " (located at slot " + minimumidx + " in the array)"); D o n e Current Future 4-4

25 Here's what the 'main' / on click handler looks like for the findminimum logic: $("#findminimum").click( function() { var nums = [10, 0,, -4, -] var minimumidx = 0; minimumidx 0 var minimumval = nums[0]; for (i in nums) { if( nums[i] < minimumval) { minimumval 10 minimumidx = i; minimumval = nums[i]; i 1 $("#findminimumoutput").html( "Smallest value is " + nums[minimumidx]+ " (located at slot " + minimumidx + " in the array)"); Done Current Future

26 Here's what the 'main' / on click handler looks like for the findminimum logic: $("#findminimum").click( function() { var nums = [10, 0,, -4, -] var minimumidx = 0; minimumidx 0 var minimumval = nums[0]; for (i in nums) { if( nums[i] < minimumval) { minimumval 10 minimumidx = i; minimumval = nums[i]; i $("#findminimumoutput").html( "Smallest value is " + nums[minimumidx]+ " (located at slot " + minimumidx + " in the array)"); Done Current Future

27 Here's what the 'main' / on click handler looks like for the findminimum logic: $("#findminimum").click( function() { var nums = [10, 0,, -4, -] var minimumidx = 0; minimumidx var minimumval = nums[0]; for (i in nums) { if( nums[i] < minimumval) { minimumval minimumidx = i; minimumval = nums[i]; i $("#findminimumoutput").html( "Smallest value is " + nums[minimumidx]+ " (located at slot " + minimumidx + " in the array)"); Done Current Future

28 Here's what the 'main' / on click handler looks like for the findminimum logic: $("#findminimum").click( function() { var nums = [10, 0,, -4, -] var minimumidx = 0; var minimumval = nums[0]; for (i in nums) { if( nums[i] < minimumval) { minimumidx = i; minimumval = nums[i]; minimumidx minimumval i 3 $("#findminimumoutput").html( "Smallest value is " + nums[minimumidx]+ " (located at slot " + minimumidx + " in the array)"); Done Current Future

29 Here's what the 'main' / on click handler looks like for the findminimum logic: $("#findminimum").click( function() { var nums = [10, 0,, -4, -] var minimumidx = 0; var minimumval = nums[0]; for (i in nums) { if( nums[i] < minimumval) { minimumidx = i; minimumval = nums[i]; minimumidx minimumval i $("#findminimumoutput").html( "Smallest value is " + nums[minimumidx]+ " (located at slot " + minimumidx + " in the array)"); Done Current Future

30 Here's what the 'main' / on click handler looks like for the findminimum logic: $("#findminimum").click( function() { var nums = [10, 0,, -4, -] var minimumidx = 0; var minimumval = nums[0]; for (i in nums) { if( nums[i] < minimumval) { minimumidx = i; minimumval = nums[i]; minimumidx minimumval i $("#findminimumoutput").html( "Smallest value is " + nums[minimumidx]+ " (located at slot " + minimumidx + " in the array)"); Done Current Future

31 ICE #3: More Parsons problems ICE #4: Use this pattern to write new code 31

32 Arrays can also be used to maintain ordered lists In one such ordering array[0] is considered the bottom of the stack. You can push a new element onto the top of the stack Or pop the top element off the stack last 1 0 last 1 0 3

LR Parsing E T + E T 1 T

LR Parsing E T + E T 1 T LR Parsing 1 Introduction Before reading this quick JFLAP tutorial on parsing please make sure to look at a reference on LL parsing to get an understanding of how the First and Follow sets are defined.