Chapter 11: Arrays CIS 275—Web Application Development for Business I

2 Array Object An Array object is a contiguous series of storage locations (_________) in memory. First, create the Array object. Then _____ the Array: var famname = new Array(3) famname[0] = "Jan Egil" famname[1] = "Tove" famname[2] = "Hege“ Use a ____ loop to write an Array (note the use of the length property of the Array object): for (i=0; i < famname.length; i++) { document.write(famname[i] + " ") }

3 Creating, Initializing, Summing Creating Arrays var n1 = new Array( 5 ); // allocate 5-element Array var n2 = new Array(); // allocate empty Array Three ways to initialize Arrays with lists var colors = new Array( “cyan”, “magenta”, “yellow”, “black” ); var integers1 = [ 2, 4, 6, 8 ]; var integers2 = [ 2,,, 8 ]; Summing elements in an Array for ( var i = 0; i < theArray.length; i++) total1 += theArray[ i ]; for ( var element in theArray) total2 += theArray[ element ];

4 Random Image Generator Random Image Generator <!-- var pictures = [ "CPE", "EPT", "GPP", "GUI", "PERF", "PORT", "SEO" ]; document.write ( "<img src = \"" + pictures[ Math.floor( Math.random() * 7 ) ] + ".gif\" width = \"105\" height = \"100\" />" ); // --> Click Refresh (or Reload) to run the script again

5 Passing Data to Functions Example var a = [ 1, 2, 3, 4, 5 ]; Pass-by-value In JavaScript, numbers and ________ values are passed to functions by value modifyElement( a[ 3 ] ); Pass-by-reference In JavaScript, references to ______ are passed to functions A reference is a location in memory modifyArray( a );

6 function start(){ var a = [ 1, 2, 3, 4, 5 ]; outputArray( "The values of the original array are: ", a ); modifyArray( a ); // array a passed by reference outputArray( "The values of the modified array are: ", a ); document.writeln( " Effects of passing array " + "element by value " + "a[3] before modifyElement: " + a[ 3 ] ); modifyElement( a[ 3 ] ); document.writeln( " a[3] after modifyElement: " + a[ 3 ] ); } function outputArray( header, theArray ){ document.writeln(header + theArray.join( " " ) + " " ); } function modifyArray( theArray ){ for ( var j in theArray ) theArray[ j ] *= 2; } function modifyElement( e ){ e *= 2; document.writeln( " value in modifyElement: " + e ); } Fig. 11.8, p. 353

7 Sorting Arrays The Array class a built-in method called _______ for sorting arrays. anArray.sort(); // uses string comparisons for sort An optional argument of sort is the name of a function called a ___________ function that compares its two arguments. anArray.sort(compareIntegers); function compareIntegers( integer1, integer2 ) { return parseInt( integer1) – parseInt ( integer2 ); }

8 sort.html Fig. 11.9, p. 355 Sorting an Array with Array Method sort function start() { var a=[10,1,9,2,8,3,7,4,6,5]; document.writeln( " Sorting an Array " ); outputArray( "Data items in original order: ", a ); a.sort( compareIntegers ); outputArray( "Data items in ascending order: ", a ); } function outputArray(header, theArray) { document.writeln( " " + header + theArray.join( " " ) + " " ); } function compareIntegers(value1, value2) { return parseInt(value1) - parseInt(value2); }

9 Searching an Array You search an array for a ______ value. The following contains the logic for a ______ search. var searchKey = “Johnson”; var element = linearSearch(anArray, searchKey); function linearSearch(theArray, key) { for ( var n = 0; n < theArray.length; ++n) if ( theArray[n] == key ) return n; return -1; } See p. 360 for the more complicated binary search (will not be covered on exam).

Multidimensional Arrays An array with two subscripts can be thought of as a table with rows and _______ (a two-dimensional array). In JavaScript, a two-dim array is a one-dim array whose elements are _________ arrays (rows). Example: var b = [ [ 1, 2], [ 3, 4 ] ]; The 1st row of Array b contains 1 in the 1st column, 2 in the 2nd column The 2nd row of Array b contains 3 in the 1st column, 4 in the 2nd column Declaring a two-dim array var b = new Array(2); b[0]=new Array(5); b[1]=new Array(3);

11 Manipulating Multi-Dim Arrays Set all elements in the 3 rd row of array a to zero: for( var col = 0; col < a[2].length; ++col) a[2][col] = 0; The same thing using for______: for( var col in a[2]) a[2][col] = 0; Determining the total of all elements in array a: var total=0; for(var row=0; row < a.length; ++row) for(var col=0; col < a[row].length; ++col) total += a[row][col]; See Fig , p. 367