Q1 Review. Other News US News top CS Universities global-universities/computer- science?int=994b08

Q1 Review

Other News• US News top CS Universitieshttp://www.usnews.com/education/best-global-universities/computer-science?int=994b08

General Problem SolvingRemember:• CS is really about solving

problems• Programming is just a means of

building these solutions

General Problem SolvingApproaching a problem is really like writing a story• The point of the story solving the

problem• The outline or structure algorithmStart by outlining the approach, in general

Example: Largest numberGiven: List of numbersOutput: The largest number in that list1. Set largest to -inf2. For each number in the list, called n

1. Compare n to largest2. Set largest to n, if n is larger

3. Output largest

Set largest to –inf

int largest = Integer.MIN_VALUE;

For each number in the list, called n

for (int n : list)

Compare n to largestSet largest to n, if n is larger

if (n > largest) {largest = n;

}

Output largest

System.out.println(largest);

int largest = Integer.MIN_VALUE;for (int n : list) {

if (n > largest) {largest = n;}

}System.out.println(largest);

Challenge ProblemIs a number in a list I give you?

Input: list, numberOutput: boolean true for yes, false for no

Basicspublic static void main(String[] args) {

…}

Always where programs start.

BasicsEverything should go inside a class (which we’ll learn more about later)

public class MyProgram {…}

Naming• Classes and complex types

should have a capitalized name–MyProgramName

• Variables should have a lower camel case name–myProgramsVariable

Data Types MatterAbsolutely most important ones are:• int (32-bit size)• double• String

Casting• You can cast to convert, with

consequences– int i = (int) 5.5;

• Other kinds of conversions require parsing, thus code to convert– int i = Integer.valueOf(“153414”);

Binary• Everything the computer sees is

binary• Know how to calculate binary

numbers• Hex is shorthand for binary• 1 hex digit = 4 bits• Byte = 8 bits

InputScanner makes your life easier.Scanner s = new Scanner(System.in);int i = s.nextInt();String string = s.next();

Output• Strings are basically the

universal form of data• System.out.print(…) tries to convert

everything to a string• System.out.println(complexObject);

Comparing StringsTo compare 2 complex types like Strings, use .equals. == is for primatives

• “Hello” == “Hello” // false• “Hello”.equals(“Hello”) // true

If• If statements control your code• Lets you determine what code

does and doesn’t execute

https://www.youtube.com/watch?v=m2Ux2PnJe6E

Syntax – Memorize!if (<condition>) {

// Do this code when condition true} else {

// Do this all other cases}

ConditionsLogical evaluations that are true/false• x == y• !(x-1 > 0 && y < 10)• (state.equals(“dead”) ||

state.equals(“sleeping”)

DeMorgan’s LawLike distribution in math• && ||• < >=• > <=• == !=!(x > 0 && y == 10) (x <= 0 || y != 10)

Short Circuit

LoopsAllows you to repeat something over and over, with small parameter changes

E.g., when finding max number, you can’t really look at an entire list of numbers at once, you quickly look at each number one by one.

For LoopsFor loops are designed for sequential looping or count based looping (most common)

for (int i = 0; i < size; i+=2) {…}

While LoopsGeneral loop to just keep repeating until a specific thing thing changes. Good for infinite loops, when you want them

boolean wantsToQuit = false;while (!wantsToQuit) {

if (input.equals(“quit”);wantsToQuit = true; // Or just break

}

Nested LoopLoop within a loop

for (int i = 0; i < 5; i++)for (int j = 0; j < 6; j++)

System.out.println(“beep”);