Programming Fundamentals: Variables and Data Storage in C

ENTI - Escola de Noves Tecnologies Interactives

UNIVERSITAT DE BARCELONA

Fonaments de programació

Variables

centre odborit a:

ENTİ Escola de Noves Tecnologies Interactives UNIVERSITAT DE BARCELONA

Conditionals

How can we store and use information?

06:54 Asap -_ Killaz 0 x O 06:09 D 12 6 O 6 O 255 23/45 PICKED UP A CLIP. 192 AMMO 91% 2 h E 5 67 ARMS 185% BULL 192 SHEL 200 50 50 En HEALTH ARMOR ellosnuncaloharian.com

Variables: Storing Information

Memory Organization

Computers store things in electronic memory, which is organized in sequential units called memory addresses.

Imagine memory as a large street where each house is identified by an address.

Addresses allow us to find and access the contents of memory at a particular location.

Lerda Grice

Computer Memory Examples

Types of Memory

Computer memory can be found for example as: • CPU Registers • L1/L2 Cache • RAM • Hard disks • Cloud storage ..

The smallest addressable unit of memory is a byte, comprised of 8 sequential bits.

Address 3 11101000 Address 2 00000000 Address 1 10010111 Address 0 01101001

Computers and Binary

Understanding Computer Logic

Remember: Computers are stupid! Computers are 100% electronics. They understand 2 things: ON and OFF. To speak to them we need to use binary.

VU 01010101010 1 1 100 100 001100 011 111001000010101 1 100100101111 11001 101100100001 10110 01 00 00100101011001 11 1000 0001011 10010110 1101 110 10 = 2 0 00011 11100100111010 01000 010110011 11001 001011010 1010010 001 010 1100011110100 10011000101:101101110188 01101000 00 11101118 1 1011010 0111011000 11 0110 000010111 4 1 4 110 101000111 10 011100000 11100010011 11 1001 0 = 0 10111111 1000111 1100001 010001 00110111 110100100 010001 01 1= 1 010 0100 0100 011000 001 10 0 1100 11 100 = 4 101001 11 = 3 011000

Variables in Programming

Storing Information with Variables

A programming language allows us to use variables to store information, without worrying about memory addresses and their content in binary

1 Variable Data

So a variable is the representation of a piece of memory that can be used to store values.

The Compiler's Role

Managing Memory Addresses

To make it easier for programmers to store information without remembering the address, the compiler manages the addresses for us.

CHILL BRO compiler dude I GOT THIS

Simplest Variable Example

Declaring and Assigning

int myVariable; myVariable = 5;

5 myVariable

Simple Program with Variables

C++ Example

#include int main() { int myVariable; myVariable = 5; printf("myVariable is %d", myVariable) ; return 0; }

Declaring Variables

Syntax and Naming Conventions

int myVariable;

This line declares a variable called "myVariable". The compiler creates a 'box' to contain the data, and manages the address for us. The data is going to be an integer, by using the int keyword. Is recommended to use always the same naming convention, we will use the lower camel case: myVariable, entio, jordiRadev, eduardArnau, lowerCamelCase ...

Initializing Variables

Assigning Values

myVariable = 5;

This line fills the variable with data. In this case, the integer 5.

Address Value Name 0x10 5 myVariable 0x14 ? ? 0x18 ? ? ... ...

Other Ways of Initializing Variables in C++

Initialization Methods

Copy initialization Direct initialization Uniform initialization

int myVariable = 5; int myVariable(5); int myVariable{ 5 } ;

This is the safest since C++11, because the compiler will warn us when we are trying to assign another value that is not safely hold by an integer

L-values and R-values

Understanding Value Categories

An l-value is a value that has an address in memory. Since all variables have addresses, all variables are l-values. L-value comes from left side, so when we do an assignment, the left hand side of the assignment operator must be an l-value. Consequently, a statement like 5 = 6; will cause a compile error, because 5 is not an l-value. The value of 5 has no memory, and thus nothing can be assigned to it.

An r-value refers to any value that can be assigned to an l-value. R-values are always evaluated to produce a single value. Examples of r-values are • single numbers (such as 4, which evaluates to 4) • variables (such as x, which evaluates to whatever value was last assigned to it) • expressions (such as x + 2, which evaluates to the value of variable x plus 2).

int x, y; X = 4; y = x + 2;

Identifier Naming Rules

Valid and Invalid Names

1. Must begin with a letter or underscore _ 2. Can only contain letters and/or numbers and/or underscore 3. Cannot contain any spaces 4. Cannot be the same as any reserved keyword

Valid names: sum myVariableName i J6x7 number_of_moves sysflag

Invalid names: sum$value number of moves 3dgame int THƯỜNG ◌͙ ...

Good Style for Naming Variables

Readability and Conciseness

It is good to give variables a logical name as it makes code easier to read BUT names which are too long are difficult to type.

e.g. bad: int theAmountOfMoneyWeMadeThisYear = 100000;

e.g. good: int moneyThisYear = 100000;

Comments in Code

Explaining Your Code

It's always very important to write understandable, self-explanatory code even if we are the only programmers working with that code.

And in order to explain and help us remember what our lines of code are doing, we can use comments, which are parts of our code that the compiler will ignore.

int money = 100000; // Amount of money made this year

Types of Comments

Single-line and Multi-line

C++ single-line comments // this is a comment - the compiler will ignore everything on this line int score = 10; // comments can come after regular statements

C-style multi-line comments /* This is a block comment. * / /* The advantage of these comments is that everything in between the start and the end symbols is ignored by the compiler, so you can have a comment which spans multiple lines */

Simple Arithmetic with Variables

Basic Operations

#include int main() { int a = 5; int b = 10; int sum = a + b; printf("The sum is %d", sum) ; return 0; result = a + b * c / d; }

Basic Arithmetic Operators

Common Symbols

Common operations (such as addition) use special symbols (such as +) that denote the operation.

. - * / These symbols are called operators. They are the same for almost all programming languages.

Variables Task

Practice Exercise

1. Create 4 different variables, a, b, c, and d; assign numbers to them, and then print them to the console.
2. Create a variable called result and make an arithmetic expression of your choice e.g. result = a + b * c / d; Print the value of result.

Operator Precedence

Mathematical Rules

We use normal mathematical precedence rules: First * and / are evaluated (going from left to right), then + and -

e.g. int result = 3 + 5 * 10; the value of resultis 53, not 80

Using Parentheses

Overruling Precedence

You can use parentheses to overrule operator precedence

int result = (3 + 5) * 10; the value of result is now 80

Undefined Behavior

C/C++ Philosophy

Undefined behavior is the result of executing code whose behavior is not well defined by the language. C and C++ don't have any rules determining what happens for example if you use the value of a variable that has not been initialized. The nature of undefined behavior is that you never quite know what you're going to get, whether you'll get it every time, and whether it'll change when you make other changes.

Remember C/C++ philosophy: "Trust the programmer"

Jordi Radev - jradev@enti.cat L FRE: ART BUTTI H