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CFT2111 Introduction to Website Development Module Leader: Matthew Mantle

CFT2111 Introduction to Website Development Module Leader: Matthew Mantle e-mail: m.e.mantle@hud.ac.uk. Arrays. var stuName=prompt("Tell me your name"); var stuMark=prompt("Tell me your mark out of 20"); var percent=stuMark/20*100;

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CFT2111 Introduction to Website Development Module Leader: Matthew Mantle

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  1. CFT2111 Introduction to Website Development Module Leader: Matthew Mantle e-mail: m.e.mantle@hud.ac.uk

  2. Arrays var stuName=prompt("Tell me your name"); var stuMark=prompt("Tell me your mark out of 20"); var percent=stuMark/20*100; document.write("<h1>"+stuName+" you got "+percent+"%</h1>"); • Previously we have worked on a program that asked the user for a test result out of 20 and displayed the user’s score as a percentage. • Imagine that we wanted to create a similar program for a tutor that would allow them to input results for an class of 20 students. • The program would then need to output a complete list of everyone’s results

  3. Based on what we know so far… var stu1Name=prompt("Enter the student name"); var stu1Mark=prompt("Enter the mark out of 20"); var stu1Percent=stu1Mark/20*100; var stu2Name=prompt("Enter the student name"); var stu2Mark=prompt("Enter the mark out of 20"); var stu2Percent=stu2Mark/20*100; var stu3Name=prompt("Enter the student name"); var stu3Mark=prompt("Enter the mark out of 20"); var stu3Percent=stu3Mark/20*100; • Need a separate variable for each student

  4. Based on what we know so far… var stu1Name=prompt("Enter the student name"); var stu1Mark=prompt("Enter the mark out of 20"); var stu1Percent=stu1Mark/20*100; var stu2Name=prompt("Enter the student name"); var stu2Mark=prompt("Enter the mark out of 20"); var stu2Percent=stu2Mark/20*100; var stu3Name=prompt("Enter the student name"); var stu3Mark=prompt("Enter the mark out of 20"); var stu3Percent=stu3Mark/20*100; if(stu1Percent>stu2Percent && stu1Percent>stu3Percent){ document.write(stu1Name+" got the highest mark"); }else if (stu2Percent>stu1Percent && stu2Percent>stu3Percent){ document.write(stu2Name+" got the highest mark"); }else if (stu3Percent>stu1Percent && stu3Percent>stu2Percent){ document.write(stu3Name+" got the highest mark"); } • What if I want the name of the student with the highest mark? • ‘else if’ statement for each possibility

  5. Arrays var stu1Name=prompt("Enter the student name"); var stu1Mark=prompt("Enter the mark out of 20"); var stu1Percent=stu1Mark/20*100; var stu2Name=prompt("Enter the student name"); var stu2Mark=prompt("Enter the mark out of 20"); var stu2Percent=stu2Mark/20*100; var stu3Name=prompt("Enter the student name"); var stu3Mark=prompt("Enter the mark out of 20"); var stu3Percent=stu3Mark/20*100; if(stu1Percent>stu2Percent && stu1Percent>stu3Percent){ document.write(stu1Name+" got the highest mark"); }else if (stu2Percent>stu1Percent && stu2Percent>stu3Percent){ document.write(stu2Name+" got the highest mark"); }else if (stu3Percent>stu1Percent && stu3Percent>stu2Percent){ document.write(stu3Name+" got the highest mark"); } • This approach is time-consuming and inefficient • Only three students in this example! • The solution is a variable that can store more than a single piece of data • An array

  6. Arrays • An array is a special type of variable. • It is a container for several pieces of data that are related in some way. • We can think of an array as being a bit like a list of information. • Each item in the list is numbered so it can be distinguished from the others • So in the previous example we could create an array called stuScores and use it to store all the student scores.

  7. Creating Arrays • Generic syntax • We can fill an array with any type of data we wish – strings, numbers, Boolean values and as many items of data as we wish. var nameOfArray = new Array("element1","element2","element3") • Examples var shopping = new Array("Tea","Bread","Milk","Cheese","Flour") var testScores=new Array(34,32,21,8,56,45) var countries = new Array("England","Scotland","Wales", "N.Ireland")

  8. Arrays • Creates a new array called shopping and fills it with pieces of text data • Each item in an array is called an element • Starting at 0 each element in the array is numbered var shopping = new Array("Tea","Bread","Milk","Cheese","Flour")

  9. Using Arrays • document.write(shopping[0]) • will output “Tea” to the page • varuserChoice=prompt("Do you like "+shopping[3]) • Asks the user if they like cheese • shopping[4]="Sugar" • Changes the 4th element in the array to sugar.

  10. Using Variables with Arrays • Often we use variables to specify the element in the array that we wish to manipulate. • The following code uses the variable counter to add data to successive elements in an array var ealing = new Array(); counter=0; ealing[counter]="Passport To Pimlico"; counter++; ealing[counter]="Kind Hearts and Coronets"; counter++; ealing[counter]="The Lavender Hill Mob"; counter++;

  11. Arrays and Loops Would output for(i=0;i<5;i++){ document.write(ealing[i]+"<br>"); } Passport To Pimlico Kind Hearts and Coronets The Lavender Hill Mob The Man in the White Suit The Ladykillers

  12. Arrays - The length property The length property tells us how many elements there are in an array • This alert statement will output 5 alert(ealing.length) Passport To Pimlico Kind Hearts and Coronets The Lavender Hill Mob The Man in the White Suit The Ladykillers for(i=0;i<ealing.length;i++){ document.write(ealing[i]+"<br>"); } • It is a good idea to use the length property with a for loop • We can change the number of elements in the array and the loop will still work

  13. Arrays and Loops var numStudents=prompt("How many students do you have?") var stuScores=new Array(); for(var i=0;i<numStudents;i++){ stuScores[i]=prompt("please give me the score for student"+i) } for(var i=0;i<stuScores.length;i++){ document.write("Student "+(i+1)+" scored "+stuScores[i]+"<br>"); } • Loops can be used to populate an Array with data • This program • Asks the user for a number of different student scores • Stores these scores in the stuScores Array • Writes a complete list of all the scores on the page

  14. Array Methods • Array methods are functions an array can perform • Often makes it easier to work with arrays • See w3schools for a complete reference http://www.w3schools.com/jsref/jsref_obj_array.asp • push() • Adds elements to an array var ealing = new Array(); ealing.push("Passport To Pimlico"); ealing.push("Kind Hearts and Coronets"); document.write(ealing) Passport To Pimlico,Kind Hearts and Coronets • splice() • Cuts an element from an array • The first number specifies the number of the element to be removed • The second element specifies how many elements to remove ealing.splice(0,1); document.write("<br>The contents of the array is now "+ealing)

  15. Finding the Highest and Lowest Values • The for loop cycles through each element in turn • If the value of the element is greater than the current largest value • This element’s value is assigned to biggestSize var shoeSize=new Array(5,5,7,9,11,7,12,6,9,10); var biggestSize=shoeSize[0]; for (i=0;i<=9;i++) { if(shoeSize[i]>biggestSize){ biggestSize=shoeSize[i] } } alert("The biggest shoe size is "+biggestSize);

  16. Parallel Arrays • Parallel arrays are used to store related data • E.g. one array for student names, another array for student scores var numStudents=prompt("How many students do you have?") var stuNames=new Array(); var stuScores=new Array(); for(var i=0;i<numStudents;i++){ stuNames[i]=prompt("Please enter a student name"); stuScores[i]=prompt("Please enter the mark for "+stuNames[i]); } • A loop is used to populate the arrays with data

  17. Parallel Arrays • Parallel arrays are used to store related data • E.g. one array for student names, another array for student scores var numStudents=prompt("How many students do you have?") var stuNames=new Array(); var stuScores=new Array(); for(var i=0;i<numStudents;i++){ stuNames[i]=prompt("Please enter a student name"); stuScores[i]=prompt("Please enter the mark for "+stuNames[i]); } for(var i=0;i<stuNames.length;i++){ document.write(stuNames[i]+" scored "+stuScores[i]+"<br>"); } • Another loop outputs the list of results

  18. var numStudents=prompt("How many students do you have?") var stuNames=new Array(); var stuScores=new Array(); for(var i=0;i<numStudents;i++){ stuNames[i]=prompt("Please enter a student name"); stuScores[i]=prompt("Please enter the mark for "+stuNames[i]); } for(var i=0;i<stuNames.length;i++){ document.write(stuNames[i]+" scored "+stuScores[i]+"<br>"); } var highestMark=stuScores[0]; for(var i=0;i<stuNames.length;i++){ if(stuScores[i]>highestMark){ highestMark=stuScores[i]; } } document.write("The highest mark was "+highestMark); Parallel Arrays • Another loop calculates the highest mark • Could have merged these two loops together

  19. Parallel Arrays • Look at the above table of data that shows a list of company employees and their wages • If an employee has performed well they get a bonus • We could store the data in the above table in ‘parallel’ arrays

  20. Parallel Arrays • Each column of the table is implemented as an array var emp=new Array("Bob","Kim","Jane","Pete","Joe"); var wages=new Array(10000,20000,21000,9000,16000); var bonuses=new Array(1000,2000,10000,10,1600);

  21. Parallel Arrays • Each column of the table is implemented as an array var emp=new Array("Bob","Kim","Jane","Pete","Joe"); var wages=new Array(10000,20000,21000,9000,16000); var bonuses=new Array(1000,2000,10000,10,1600); document.write(emp[2]+" earns £"+wages[2]); Jane earns £21000

  22. Parallel Arrays var emp=new Array("Bob","Kim","Jane","Pete","Joe"); var wages=new Array(10000,20000,21000,9000,16000); var bonuses=new Array(1000,2000,10000,10,1600); var name=prompt("Enter an employee name") var indexNum; for(var i=0;i<emp.length;i++){ if(name==emp[i]){ indexNum=i; } } document.write(name+" has a basic wage of £"+wages[indexNum]+" and a bonus of £"+bonuses[indexNum]) • Imagine I want the details for an employee

  23. Parallel Arrays var emp=new Array("Bob","Kim","Jane","Pete","Joe"); var wages=new Array(10000,20000,21000,9000,16000); var bonuses=new Array(1000,2000,10000,10,1600); var name=prompt("Enter an employee name") var indexNum; for(var i=0;i<emp.length;i++){ if(name==emp[i]){ indexNum=i; } } document.write(name+" has a basic wage of £"+wages[indexNum]+" and a bonus of £"+bonuses[indexNum]) • A prompt box asks the user for the name of an employee

  24. Parallel Arrays var emp=new Array("Bob","Kim","Jane","Pete","Joe"); var wages=new Array(10000,20000,21000,9000,16000); var bonuses=new Array(1000,2000,10000,10,1600); var name=prompt("Enter an employee name") var indexNum; for(var i=0;i<emp.length;i++){ if(name==emp[i]){ indexNum=i; } } document.write(name+" has a basic wage of £"+wages[indexNum]+" and a bonus of £"+bonuses[indexNum]) • We loop through each value in the emp array to find a match for the name the user entered.

  25. Parallel Arrays var emp=new Array("Bob","Kim","Jane","Pete","Joe"); var wages=new Array(10000,20000,21000,9000,16000); var bonuses=new Array(1000,2000,10000,10,1600); var name=prompt("Enter an employee name") var indexNum; for(var i=0;i<emp.length;i++){ if(name==emp[i]){ indexNum=i; } } document.write(name+" has a basic wage of £"+wages[indexNum]+" and a bonus of £"+bonuses[indexNum]) • If we find a match for the user’s entry we store the index number of the array element • e.g. if the user entered ‘Joe’ indexNum will have a value of 4

  26. Parallel Arrays var emp=new Array("Bob","Kim","Jane","Pete","Joe"); var wages=new Array(10000,20000,21000,9000,16000); var bonuses=new Array(1000,2000,10000,10,1600); var name=prompt("Enter an employee name") var indexNum; for(var i=0;i<emp.length;i++){ if(name==emp[i]){ indexNum=i; } } document.write(name+" has a basic wage of £"+wages[indexNum]+" and a bonus of £"+bonuses[indexNum]) • Finally we can output the details for the person using the indexNum variable

  27. var emp=new Array("Bob","Kim","Jane","Pete","Joe"); var wages=new Array(10000,20000,21000,9000,16000); var bonuses=new Array(1000,2000,10000,10,1600); var finalSalary=new Array(); for(var i=0;i<emp.length;i++){ var bonus=prompt("Should "+emp[i]+" be paid a bonus?"); if(bonus=="yes" || bonus=="Yes"){ finalSalary[i]=wages[i]+bonuses[i]; }else{ finalSalary[i]=wages[i]; } } for(var i=0;i<emp.length;i++){ document.write(emp[i]+"'s final salary is £"+finalSalary[i]+"<br>"); } Parallel Arrays • Bonuses are not guaranteed • Imagine I am writing a program that calculates an employee’s wage based on whether or not they deserve a bonus

  28. Parallel Arrays var emp=new Array("Bob","Kim","Jane","Pete","Joe"); var wages=new Array(10000,20000,21000,9000,16000); var bonuses=new Array(1000,2000,10000,10,1600); var finalSalary=new Array(); for(var i=0;i<emp.length;i++){ var bonus=prompt("Should "+emp[i]+" be paid a bonus?"); if(bonus=="yes" || bonus=="Yes"){ finalSalary[i]=wages[i]+bonuses[i]; }else{ finalSalary[i]=wages[i]; } } for(var i=0;i<emp.length;i++){ document.write(emp[i]+"'s final salary is £"+finalSalary[i]+"<br>"); } • Create a new empty array

  29. Parallel Arrays var emp=new Array("Bob","Kim","Jane","Pete","Joe"); var wages=new Array(10000,20000,21000,9000,16000); var bonuses=new Array(1000,2000,10000,10,1600); var finalSalary=new Array(); for(var i=0;i<emp.length;i++){ var bonus=prompt("Should "+emp[i]+" be paid a bonus?"); if(bonus=="yes" || bonus=="Yes"){ finalSalary[i]=wages[i]+bonuses[i]; }else{ finalSalary[i]=wages[i]; } } for(var i=0;i<emp.length;i++){ document.write(emp[i]+"'s final salary is £"+finalSalary[i]+"<br>"); } • A loop is used to ask the user if each employee deserves their bonus • E.g. when i has a value of 2 the prompt box will ask ‘Should Jane be paid a bonus ‘

  30. Parallel Arrays var emp=new Array("Bob","Kim","Jane","Pete","Joe"); var wages=new Array(10000,20000,21000,9000,16000); var bonuses=new Array(1000,2000,10000,10,1600); var finalSalary=new Array(); for(var i=0;i<emp.length;i++){ var bonus=prompt("Should "+emp[i]+" be paid a bonus?"); if(bonus=="yes" || bonus=="Yes"){ finalSalary[i]=wages[i]+bonuses[i]; }else{ finalSalary[i]=wages[i]; } } for(var i=0;i<emp.length;i++){ document.write(emp[i]+"'s final salary is £"+finalSalary[i]+"<br>"); } • If the user answers ‘yes’ or ‘Yes’ the value of bonuses is added to the value of wages to create a finalSalary value • E.g. when i is 2, if the user says Jane is worth her bonus finalSalary[2] will have a value of 31000 (21000+10000)

  31. Parallel Arrays var emp=new Array("Bob","Kim","Jane","Pete","Joe"); var wages=new Array(10000,20000,21000,9000,16000); var bonuses=new Array(1000,2000,10000,10,1600); var finalSalary=new Array(); for(var i=0;i<emp.length;i++){ var bonus=prompt("Should "+emp[i]+" be paid a bonus?"); if(bonus=="yes" || bonus=="Yes"){ finalSalary[i]=wages[i]+bonuses[i]; }else{ finalSalary[i]=wages[i]; } } for(var i=0;i<emp.length;i++){ document.write(emp[i]+"'s final salary is £"+finalSalary[i]+"<br>"); } • I use another loop to output the complete list of employees and their final salaries

  32. Next week • Practical Session • Arrays • The Assignment

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