10-13 Test 2 Review

Chapter 3  JavaScript

<SCRIPT LANGUAGE="JavaScript"> to add JavaScript

Variables:
  place holder for a value 
  has a name: can't be reserved word (keyword) 
      can't have spaces
      has to start with a letter and contain letters or numbers
          ($ and _ are letters)
      case sensitive theNumber != thenumber != THENUMBER
      
  declare:
      var userName;
      
  initialize:
      userName="Guest";   (the = is assignment)
      
  data: (what can be in a variable?)
      Numbers: 1, 3.14
      Strings: "This is a string", "Enter your name.", "", "1234"
      Logical: (Boolean) true, false
      null: no value in the variable (a value that represents no value)
      Undefined
  
Expression:
    ((x + 3) * 7)/10
    (x*y) <= 100
      
Operators:
  arithmetic: +, -, *, /, %, ++, --
  comparison: <, >, <=, >=, ==, !=  (produce true or false)
  string: +
      "Hi" + "tHere"  is "HitHere"
      "3" + "5" is "35"
  logical:  &&, ||, !
      (x > 0 && x <= 100) 
      (x < -100 || x > 100) x is really negative OR x is really positive
      !(x > 10)  it is not the case that x is larger than 10

Control Structures:
   Selection: if statements
        - keyword "if"
        - (condition) 
        - { the body --entered if the condition is true }
        
        -optional: else{} , else if (condition){}
        
     if(x < 0) {
        document.writeln("Negative");
     }
     else if(x > 0){
        document.writeln("Positive");
     }
     else {
        document.writeln("Zero");
     }
  
  Iteration: while loops
      - some initialization: a place to start (usually makes the condition true)
      - keyword "while"
      - (condition)
            if true -- executes body of the loop, checks the condition again
            if false -- skips the body of the loop
      - { body of loop }
            -some statement that will eventually make the condition false
            
      var count = 1;
      while(count < 129){
        document.writeln(count);
        count = 2*count;
      }
      
      var answer="";
      while(answer != "quit"){
        answer = prompt("What next?", "Type here.");
        alert("You said, " + answer);
      }
  
  
  Functions:
      usually defined in the HEAD section.
      - keyword "function"
      - name: same rules for variables
      - (parameter list)
      - { function body }
          - contains other statements (ifs, whiles, etc)
          - return statement
          
      //script in the HEAD section    
     function printName (theName)
     {
        document.writeln("My Name is " + theName);
     }
     
     function printMyName(){
        document.writeln("My Name is Clif");
     }
     
     function getLargest(x, y, z){
        var result;

        if(x >= y && x >= z){
           result = x;
        }
        else if(y >= x && y >= z){
            result = y;
        }
        else if(z >= x && z >= y){
            result = z;
        }
     
        return result;
     }
     
     //script in the body
     //when I want to use it:
     printName("Clif");
     printName("Bob");
     var name = "Sue";
     printName(name);
     printName(name + " Johnson");
  
      var large = getLargest(10, -20, 500);