Update Computer Science.md

Grade 9/Computer Science.md

@@ -57,3 +57,343 @@
 > |double|-1.7e<sup>+/-308</sup> to 1.7<sup>+/-308</sup>|64 bits|stuff|double stuff;|
 > |char|Single (unicode) characters|16 bits|letter|char letter;|
 
+> ## Operations
+
+>> |Operation|Notation|Equivalent|Result Type|
+>> |:--------|:-------|:---------|:----------|
+>> |equals|a == b||boolean|
+>> |addition|a + b||number|
+>> |subtraction|a - b||number|
+>> |multiplication|a * b||number|
+>> |division|a / b||number|
+>> |less|a < b||boolean|
+>> |less or equal|a > b|a <= b||boolean|
+>> |more|a >= b|not (a < b)|boolean|
+>> |more or equal|a >= b|not(a == b)|boolean|
+>> |negation|-b|0 - b|number|
+
+> ## Sample Code
+>> ``` java
+>> class AddTip{
+>>    public static void main(String[]args){
+>>      double amount; // variable declaration, 
+>>                     // can store a double(real number)
+>>                     // no value assigned to it yet
+>>                     // variable name is identifier
+>>      double pi = 3.1415926;
+>>      amount = 19.95;  // variable amount has been assigned value of 19.95
+>>      amount = amount + 3.00; // takes current vaue of amount(19.95) and add 3.00 to it
+>>                              // then assigns the new value to amount(22.95)
+>>      System.out.print("We will pay $");
+>>      System.out.print(amount);
+>>      System.out.print(" for the pizza delivery");
+>>      // prints amount
+>>    }
+>> }
+>> ```
+
+> ## Java Data Types
+>> ### Java primitive types
+>>> boolean      
+
+>>> number:    
+>>> - integer
+>>>   - byte
+>>>   - short
+>>>   - int
+>>>   - long
+>>>   - char
+>>> - floating-point
+>>>   - float
+>>>   - double
+
+>>> **Remember** ```String``` is not a primitive type      
+
+>> ### Boolean Expressions
+>>> can only have 2 possible value(true or false)     
+>>>  - compare must be compatible type     
+
+>>> |Symbol|Meaning|
+>>> |:-----|:------|
+>>> |==|equal to|
+>>> |!=|not equal to|
+>>> |>|greater than|
+>>> |<|less than|
+>>> |>=|greater than or equal to|
+>>> |<=|less than or equal to|
+
+>> ```Modulus operator (%)```: returns the remainder of 2 numbers        
+>> ```String```: stores characters / text     
+>> ```String comparison```: different from primitive type comparison     
+>>   - cannot use ```==``` sign
+>>   - use boolean expression ```object1.equals(object2)```
+
+> ## Reading Input (Scanner Class)
+
+>> ```import``` scanner class to use it      
+>> use 
+>> ```java 
+>> import java.util.Scanner;  
+>> ``` 
+>> to tell compiler to include scanner class in the .class file       
+>> line at very top of file
+>> create scanner using 
+>> ```java
+>> Scanner myScanner = new Scanner(System.in);
+>> ```
+
+>> |To read this...|...Make this method call|
+>> |:--------------|:-----------------------|
+>> |a number with no decimal point in it|nextInt()|
+>> |a number with a decimal point in it|nextDouble()|
+>> |a word(ending in a blank space, for example)|next()|
+>> |a line(or what remains of a line after you've already read some data from the line)|nextLine()|
+>> |a single character(such as a letter, a digit or a punctuation character|next.charAt(0)|
+
+
+> ## Selection statements
+>> allow java to make a decision     
+>> depending on decision, program will function differently each time it is run      
+
+>> ```java
+>> if(condition){
+>>    //then perform some commands
+>>    // outcome
+>> }
+>>```
+
+>> ### Example:
+
+>>> ```java
+>>> int age = 17;
+>>> if(age >= 16){
+>>>     // execute if condition
+>>>     System.out.println("You are " + age);
+>>>     System.out.println("You can learn to drive");
+>>> } // skips if condition not met
+>>>```
+
+>> ### ```=``` vs ```==```
+>>> ```=```: assignment    
+>>> ```==```: comparison    
+
+>> ### if.... else if.... else
+
+>>> ```java
+>>> if(condition){
+>>>    statement1;
+>>> } else{
+>>>    statement2;
+>>> // -----------------------
+>>> }
+>>> if(num > 10){
+>>>    System.out.println("Your number is greater than 10");
+>>> } else{
+>>>    System.out.println("Your number is less than or equal to 10");
+>>> }
+>>> ```
+
+>>>  - used when program needs to choose from a variety of situations
+>>>  - use else if to specify another condition
+>>>  - helps to control the flow of your program
+>>>  - helps make decision when 3 or more conditions must be considered
+>>>  - makes program more efficient
+
+>>> ```java
+>>> if(age >= 16){
+>>>    System.out.println("You can drive");
+>>> }else if(age == 15){
+>>>    System.out.println("You can drive next year");
+>>> }
+>>> ```
+>>>  - else if statement is additonal part of if statement     
+>>>  - can be multiple else if statement in a single if construct     
+>>>  - one if statement can only run one outcome       
+
+>> else - used to specify outcome that will be run if one other conditions are met      
+>> debugging - the process of finding out and correcting erros in a program       
+
+> ## Types of Errors
+
+>> ```Compile-Time-Errors``` - Complier checks syntax
+>> - syntax error - how you write your statements(your grammar)
+>>    - Spelling mistakes      
+>>    - Punctuation errors    
+>>    - Missing brackets, curly brackets, key words
+>> - Incompatible types of data    
+>> - .class file not created      
+
+>> ```Logical Error``` - Hardest to detect/solve
+>>  - compiles and runs correctly but incorrect results
+>>  - wrong formula
+>>  - wrong approach taken
+
+>> ```Run-time Error``` - occur during program execution
+>>  - causes program to terminate abnnormally
+>>  - try dividing by zero
+
+
+> ## Logical Statements
+>> True/False     
+>> 3 basic logical operator
+>>  ```OR/AND/NOT```
+
+>> **```AND```**: when all values are true
+>> **```OR```**: when at least one value is true
+>> **```NOT```**: flips the value of a statement
+
+>> ### Truth Table
+>>> Used to study logic by computer scientists
+
+>>> | X | Y |X OR Y|X AND Y|
+>>> |:--|:--|:-----|:------|
+>>> |T|T|T|T|
+>>> |T|F|T|F|
+>>> |F|T|T|F|
+>>> |F|F|F|F|
+
+>> operator precendence - evaluate left to right
+>> 1. AND( & & ) - checks first statement, if it is true, check the second one
+>> 2. OR( | | ) - checks the first statement and second statement
+>> 3. NOT( ! ) - reverses the statement
+
+> ## Loops
+
+>> Allows coders to repeat code     
+>> Exit condition in loop      
+
+>> ```java
+>> while(condition){
+>>  // do something
+>> }
+>> ```
+
+>> ### While Loops
+>>> consists of a condition statement that are executed while the condition is true      
+>>> types of conditions used in a while statement are the same as in the ```if statement```     
+>>> while the condition is true, repeat the statements in the loop
+
+>>> ```java
+>>> while(num <= 10){
+>>>    System.out.println("Enter a number higher than 10.");
+>>>    num = scan.nextInt();
+>>> }
+>>> ```
+
+>>> the program continues repeating until the num is greater than 10      
+>>> there may be times when you may want to specify more than one condition     
+>>> no limit to the number of conditions, but should limit to 2 or 3     
+>>> can combine conditions(logical statements) using ```&&``` and ```||``` conditional  operators
+
+>>> ```java
+>>> while(num >= 1 && num <= 10){ // runs until num is between 1 and 10
+>>>     num = myScanner.nextInt();
+>>> }
+>>> ```
+
+>> Incrementing By One
+>> ``` java
+>>   mynumber = mynumber + 1;
+>>   // is the same as:
+>>   mynumber += 1;
+>>   // is the same as:
+>>   mynumber++;
+>> 
+>> ```
+
+>> Why counter: To keep track of how many times a loop has executed     
+
+>> ```java
+>> int counter = 0;
+>> int guess = 0;
+>> while(guess != 7){
+>>    System.out.println("Guess a number between 1 and 10");
+>>    guess = scan.nextInt();
+>>    counter++;
+>> }
+>> System.out.println("It took you " + counter + " tries!");
+>> ```
+
+
+>> ### For Loops
+>>> include three distinct statements separated by semicolon     
+>>> first statement declares the counter variable           
+>>> second statement specifies exit condition    
+>>> third statement increments the counter variable after each iteration of the loop
+>>> counter variable only exists within loop
+
+>>> ```while``` and ```for``` loop: - may not need to run if condition is false
+
+>>> ```java
+>>> for(int i = 0; i < 10; i++){ // this loop runs 10 times
+>>>     // do stuff here
+>>> }
+>>> ```
+
+>> ### Accumulator
+>>> variables that add any value to a sum or total      
+>>> realize the need for the variable     
+>>> declare the variable
+>>> initialize it (give it a start value, usually 0)
+>>> accumulate the value in a loop (add the value to the variable)
+
+>> ### Do while Loop
+
+>>> They must runu minimum once
+>>> After running once, it checks the continue condition at the end of the iteration
+
+>>> ```java
+>>> do{
+>>>   // do stuff here
+>>> }while(condition);
+>>> ```
+
+>>> Example
+
+>>> ```java
+>>> public static void main(String[]args){
+>>>    Scanner sc = new Scanner(System.in);
+>>>    int total = 0, value;
+>>>    do {
+>>>       System.out.println("Enter values to sum and 0 to quit");
+>>>       value = input.nextInt();
+>>>       total = total + value;
+>>>    }while(value != 0);
+>>>    System.out.println("Your total is: " + total);
+>>> }
+>>> ```
+
+> ### Random Number Generation
+>> ### Method 1
+
+>> ```java
+>> import java.util.Random;
+>> public class {
+>>     public static void main(String[]args){
+>>         Random randGen = new Random();
+>>         int randNumber = randGen.nextInt(100) + 1;
+>>     }
+>> }
+>> ```
+
+>> ### Method 2   
+
+>> using Math class
+
+>> ```java
+>> int myRandNumber = (int) (Math.random() * 100) + 1;
+>> ```
+
+
+# Unit 2 Arrays
+
+> ```Arrays```: a data structure that allow you to hold multiple pieces of data, in a single object     
+>   - hold a predetermined number of elements
+>   - must be same type
+
+
+
+
+
+
+