Logic and Control

4-2 Decision (selection) structure: if (condition) { statement etc. } Example: if (age == 15) { document.write(“ you are a fifteen”); }

4-3 A relational operator (aka comparison operator) determines whether a specific relationship exists between two values. Table 4-1 Relational operators

4-4 Examples: if (age > 90)… if (size < 10)… if (sum <= 50)… if (theNumber == 100)… if (x != 100)…

4-5 Examples: if (age > 90) { document.write (“you are a bit old”); } if (size< 10) { document.write (“you are just the right size”); } if (total >= 0) { total += 50; } if (name == “jasmine”) { document.write (“nice name!”); }

4-6 if (condition) { statement etc. } else { statement etc. }

4-7 if (age >= 20) { document.write(“you are an adult”); } else { document.write(“you are NOT an adult”); } if (salary <= 10) { document.write(“you need a raise”); } else { document.write(“you make a fine salary”); }

4-8 Concept: You can compare strings. This allows you to create decision structures that test the value of a string. If (password == “blahblah”) { document.write(“that is the correct password”); } else { document.write(“that is the correct password”); }

4-9 Other String Comparisons Figure 4-10 Character codes for the strings 'Mary' and 'Mark' Figure 4-11 Comparing each character in a string

4-10 The if-else if - else Statement if (condition_1) { statement etc. } else if (condition_2){ statement etc. } else{ statement etc. }

4-11 if (score < 60) { document.write(‘Your grade is F.’); } else if (score < 70) { document.write( ‘Your grade is D.’); } else if score < 80: { document.write( ‘Your grade is C.’); } else if score < 90 { document.write( ‘Your grade is B.’); } else { document.write( ‘Your grade is A.’); }

 isNaN( ) – determines whether a number is legal  Returns True (if not a number)  or False (if it is a number)  NaN is an abbreviation for: Not a Number  Examples of nonNumbers:  A string  A number divided by 0  alert(isNaN(4)) will return false  alert(isNaN(“four”)) will return true

 Logical operators are used to determine the logic between variables or values.  Given that x=6 and y=3, the table below explains the logical operators: Operator Description Example && and (x 1) is true || or (x==5 || y==5) is false ! not !(x==y) is true

 Many times you will need to check multiple conditions within the same statement  Logical Operators allow you to check multiple conditions:  Examples: if ((x > 100) && (x < 1000)) … if (age 65) …

 The innerHTML property sets or returns the inner HTML of an element.  We will use it to set error messages on fields Example: Styling error message #Nerror {color:red;} The input field with place for error message Setting the innerHTML of the span element to conatin error message document.getElementById(" Nerror ").innerHTML = "Must be numeric";

5-16 A condition-controlled loop uses a true/false condition to control the number of times that it repeats. while (number < 20) … while (password != passwordOnFile)… while (isNaN(ans))…

5-17 while (condition) { statement etc. }

5-18 The loop will continue to run as long as count is less than, or equal to 5. var count = 1;//set count to have a value of 1 while (count <= 5)//this is the condition being tested { document.write(count + " "); count++;// this will increment the count by 1 } If the condition (count <= 5) is true, the statements inside the brackets are executed and then the loop starts over If the condition is false, the statements inside the brackets are skipped and the program exits the loop

5-19 Programs that calculate the total of a series of numbers typically use two elements: A loop that reads each number in the series A variable that accumulates the total of the numbers as they are read.

5-20 for (var=startvalue; var<=endvalue; var=var+increment) { code to be executed… } var i = 1; for (i = 1; i <= 5; i++)…

5-21 The example below defines a loop that starts with count=0. The loop will continue to run as long as count is less than, or equal to 5. count will increase by 1 each time the loop runs. var i=0; for (i=0; i "); }

 Loops used extensively when working with arrays  Example: var fruits = [‘apple’, ‘peach’, ‘orange’]; var counter = 0; while (counter < fruits.length) { document.write(fruits[counter]) + ‘ ‘); counter++; }

function functionName ( ) { some code goes in here…. }  function – keyword, tells browser you are declaring a function  functionName – the name you choose to call the function  ( ) - place for parameters, extra info the function may need  { - show the beginning of function code  } – shows the end of the function code

 Functions only execute if they are called!!  Good Practice – place function definitions in at the top of the head section  You can call a function in the head section or the body section  To call a function, provide the function name and the parameters (if any)  Example: doSomething( );

 Used to supply 1 or more values to a function  Set in the function header inside the parenthesis  General format: function doSomething(var1, var2) //this is a function header  When you make a function “call”, you need to supply the parameters  Example: doSomething(myVar1, myVar2) //this is a function call

 Used to return a value from a function  Place the return statement as the last line of the function  The value is returned to the place in the main script where the function was called  You need to save the returned value in a variable

 When a variable is created by an assignment statement inside the function, the variable is local to that function  Can be assigned or modified in the function  Once the function is done (hit the closing bracket }), variable dies – value cannot be used outside of function  The variable does not exist outside the function!