COMP 110 Designing Programs Luv Kohli August 27

COMP 110 Designing Programs Luv Kohli August 27, 2008 MWF 2 -2: 50 pm Sitterson 014 1

Announcements Office Hours ◦ After class today ◦ Come if you don’t have j. GRASP working 2

Questions? 3

Today in COMP 110 Writing algorithms in pseudocode Variables and primitive types

Fun exercise time 5

Algorithm A set of instructions for solving a problem 6

Pseudocode combination of code and English used to express an algorithm before writing algorithm into code 7

Variables Used to store data in a program The data currently in a variable is its value Name of variable is an identifier Can change value throughout program Choose variable names that are meaningful!

Variables and Memory A variable corresponds to a location in memory variable n 1 • Use this cell to store the value of n 1 main memory • Prevent this cell from being used by other variables later

How to use variables Declare a variable Assign a value to the variable Change the value of the variable

Variable Declarations Syntax: ◦ Type Variable_1, Variable_2, …; Examples: ◦ int count, score, my. Int; ◦ char letter; ◦ double total. Cost, ratio; ◦ int fjiofeu; // not a useful name! 11

How to name a variable Letters, digits (0 -9), underscore (_) First character cannot be a digit Java is case sensitive Legal names ◦ pink. Floyd, the_coup, b 3 atles Illegal names ◦ michael. bolton, kenny-G, 1 CP 12

Keywords Reserved words with predefined meanings You cannot name your variables keywords if, else, return, new See Appendix 1 in the textbook 13

Type What kind of value the variable can hold. Two kinds of types. ◦ Primitive type - indecomposable values Names begin with lowercase letters int, double, char, boolean See section 2. 1 for a full list ◦ Class type - objects with both data and methods Names begin with uppercase letter Scanner, String 14

Primitive Types Integer (byte, short, int, long) ◦ 0, -3, 5, 43 Floating-point number (float, double) ◦ 0. 5, 12. 4863, -4. 3 Characters (char) ◦ A, r, %, T Boolean (boolean) ◦ true, false 15

Primitive Types: small to big

Variables and Memory When declaring a variable, a certain amount of memory is assigned based on the declared primitive type int age; double length; char letter; main memory

Assignment Statements Change a variable’s value Syntax: ◦ variable = expression; Example: ◦ sleep. Needed = 8; ◦ sleep. Desired = sleep. Needed * 2;

Behind the statement variable = expression; ◦ CPU calculates the value of the expression. ◦ Send the value to the location of variable. sleep. Desired = sleep. Needed * 2; ◦ Calculate sleep. Needed * 2 Get the current value of sleep. Needed from its memory location ◦ Assign the value to the location of sleep. Desired

Specialized Assignment Operators length *= 5; // is the same as length = length * 5; age ++; // is the same as age = age + 1;

Assignment compatibilities Usually, we need to put values of a certain type into variables of the same type However, in some cases, the value will automatically be converted when types are different int age; age = 10; double length; length = age ;

Assignment Compatibilities byte->short->int->long->float->double ◦ my. Short my. Int; ◦ my. Byte my. Long; ◦ my. Float my. Byte; ◦ my. Long my. Int; 22

Type Casting You can ask the computer to change the type of values which are against the compatibility. my. Float = my. Double; my. Byte = my. Int; my. Short = my. Float; my. Float = (float)my. Double; my. Byte = (byte)my. Int; my. Short = (short)my. Float; 23

Arithmetic Operators Unary operators (more info later) ◦ +, -, ++, --, ! Binary arithmetic operators ◦ *, /, %, +, rate*rate + delta 1/(time + 3*mass) (a - 7)/(t + 9*v) 24

Modular Arithmetic - % “clock arithmetic” ◦ Minutes on a clock are mod 60 Remainder 7 % 3 = 1 (7 / 3 = 2, remainder 1) 8 % 3 = 2 (8 / 3 = 2, remainder 2) 9 % 3 = 0 (9 / 3 = 3, remainder 0) 25

Homework Program 1 is on the web page We will look at code in recitation that will help you

Friday Recitation (bring charged laptop and textbook) Lab 1 Programming help for Program 1 27