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ECMM6018 Enterprise Networking For Electronic Commerce Tutorial 4

ECMM6018 Enterprise Networking For Electronic Commerce Tutorial 4. Client Side Scripting JavaScript Looping. Types of Looping. While Do While For. While Statement. loops through a block of code while a condition is true Syntax while (condition) {

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ECMM6018 Enterprise Networking For Electronic Commerce Tutorial 4

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  1. ECMM6018 Enterprise Networking For Electronic CommerceTutorial 4 Client Side Scripting JavaScript Looping

  2. Types of Looping • While • Do While • For

  3. While Statement • loops through a block of code while a condition is true • Syntax while (condition) { code to be executed } • JavaScript is case sensitive while ≠ WHILE • N.B. All JavaScript reserved keywords are case sensitive After the while statement is executed program flows to the next statement after the while is finished

  4. While Statement ctd. • The while statement can be used in 2 ways • 1.) The number of repetitions is known in advance e.g. calculating the average of a class. <html> <head> <title>Class Average Program</title> <script language=“JavaScript”> var total, gradeCounter, gradeValue, average, grade; total = 0; gradeCounter =1;

  5. While Statement ctd. while (gradeCounter <=10) { grade = window.prompt (“Enter integer grade:”, “0”); gradeValue = parseInt(grade); total = total +gradeValue; gradeCounter = gradeCounter + 1; } average = total /10; document.writeln(“<H1>” Class average is “ +average + “</H1>”); </script>

  6. While Statement ctd. </head> <body> Some Text Here </body> </html>

  7. While Statement using a sentinel value • 2.) Where the number of repetitions is not known in advance. In this scenario a value known as a sentinel value is used as a stopping value. <html> <head> <title>Class Average Program</title> <script language=“JavaScript”> var total, gradeCounter, gradeValue, average, grade; total = 0; gradeCounter =0;

  8. While Statement using a sentinel value grade = window.prompt(“Enter Integer Grade, -1 to Quit:”, “0”); gradeValue = parseInt(grade); while (gradeValue != -1) { total = total + gradeValue; gradeCounter = gradeCounter +1; grade = window.prompt(“Enter Integer Grade, -1 to Quit: “, “0”); gradeValue = parseInt(grade); }

  9. While Statement using a sentinel value if (gradeCounter !=0) { average = total/gradeCounter; document.writeln(“<H1>Class average is “ +average + “</H1>”); } else { document.writeln(“<H1>Class average is “ +average + “</H1>”); } </script>

  10. While Statement using a sentinel value </head> <body> Some text </body> </html>

  11. Do While Statement • Loops through the block at least once • Syntax do { code to be executed } while (condition); example <html> <body> <script type="text/javascript"> i = 0

  12. Do While ctd. do { document.write("The number is " + i) document.write("<br>") i++ } while (i <= 5); </script> </body> </html>

  13. The For Loop • run statements a specified number of times • Requires: - the name of a control variable - its initial value - the increment/decrement by which the loop counter is modified - the testing condition for the final value

  14. For Loop ctd. • Syntax for(initialization; test condition; increment) { code to be executed; } • Example <html> <head> <title>Sum the Even Integers from 2 to 100</title>

  15. For Loop ctd <script language = “JavaScript”> var sum = 0; for (var number =2; number<=100; number +2) { sum += number; } document.writeln(“<H1>”The sum of the even integers “ + “ from 2 to 100 is “ +sum + “</H1>”); </script> </head> <body> </body> </html>

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