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Chapter 11: Arrays

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

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Chapter 11: Arrays

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  1. 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] + "<br />") }

  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 <html xmlns = "http://www.w3.org/1999/xhtml"> <head> <title>Random Image Generator</title> <script type = "text/javascript"> <!-- var pictures = [ "CPE", "EPT", "GPP", "GUI", "PERF", "PORT", "SEO" ]; document.write ( "<img src = \"" + pictures[ Math.floor( Math.random() * 7 ) ] + ".gif\" width = \"105\" height = \"100\" />" ); // --> </script> </head> <body> <p>Click Refresh (or Reload) to run the script again</p> </body> </html>

  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. <script type = "text/javascript"> 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( "<h2>Effects of passing array " + "element by value</h2>" + "a[3] before modifyElement: " + a[ 3 ] ); modifyElement( a[ 3 ] ); document.writeln( "<br />a[3] after modifyElement: " + a[ 3 ] ); } function outputArray( header, theArray ){ document.writeln(header + theArray.join( " " ) + "<br />" ); } function modifyArray( theArray ){ for ( var j in theArray ) theArray[ j ] *= 2; } function modifyElement( e ){ e *= 2; document.writeln( "<br />value in modifyElement: " + e ); } </script> 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. <html xmlns = "http://www.w3.org/1999/xhtml"> <head> <title>Sorting an Array with Array Method sort</title> <script type = "text/javascript"> function start() { var a=[10,1,9,2,8,3,7,4,6,5]; document.writeln( "<h1>Sorting an Array</h1>" ); outputArray( "Data items in original order: ", a ); a.sort( compareIntegers ); outputArray( "Data items in ascending order: ", a ); } function outputArray(header, theArray) { document.writeln( "<p>" + header + theArray.join( " " ) + "</p>" ); } function compareIntegers(value1, value2) { return parseInt(value1) - parseInt(value2); } </script> </head> <body onload = "start()“> </body> </html> sort.html Fig. 11.9, p. 355

  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).

  10. 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 3rd 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. 11.14, p. 367

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