lecture 2: programming basics & variables

LECTURE 2:PROGRAMMING BASICS & VARIABLES

CSC 107 – Programming For Science

Announcements

Initial set of slides had wrong day for midterm Correct date on syllabus and in Angel

Midterm is on October 21

Class time is not 60 minutes, but 75 minutes I screwed this up on Tuesday and wanted to

apologize If time permits, still have Tuesday’s actual

activity(otherwise I will post it & solution to Angel)

History of C

Dennis Ritchie developed C from 1969 – 1973

Based upon B (& other) earlier languages Since its creation, language grown

organically Tradition of adding features beyond standard

as desired

History of C++

Bjarne Stroustrup created to add “objects” Also included many other improvements to

language Name is inside joke: "++" is increment

operator in C Updated for quick growth

2.0 release in 1989 1998 adopted as ISO standard C++ 201x in development now

C Versus C++C++ is designed to be

as compatible with C as possible, thereby

providing a smooth transition from C

C Versus C++

C++

C

C Versus C++

C

C Versus C++

Latest definition of C added most C++ features Not classes & objects, these only found in

C++ For this reason, also not a part of CSC 107 Differences now minimal and easily

avoided Once objects removed, C++ just

“looser” C Removes annoying restrictions that had

been in C Since makes life easier, often supported in

C anyway

Computers are VERY, VERY stupid

Computers have no common-sense They will only do what you tell them to do NOT what you want them to do, which

often differs

While this is true for every computer does Programming highlights exactly how this

happens As you will see, C++ does nothing to

prevent issues

Computers have no common-sense They will only do what you tell them to do NOT what you want them to do, which

often differs

Case-Sensitivity

Example of computers being very literal And language not helping by fixing what you

say

main, Main, & MAiN treated as different words Case of the letters matters, not just the

words Could be different, so C++ won’t change Main to main

Can help prevent easy mistakes from swapping names

With just a little practice, becomes second nature

“Whitespace”

One (very small) way C++ actually helps you C++ treats whitespace equally – spaces,

enters, & tabs Whether 1 or 1000000000000 – all will be

ignored Cannot use in symbol, whitespace

splits words Treats these as different “: :” and “::”

Spaces between words needed, but not counted Wecansplitwordsbutthecomputercannot

Your First C++ Program

#include <iostream>using std::cout;

int main() { /* Hi, Mom. This is a comment

that goes over 2 line. */ std::cout << “Hello world!”; return 0; // This comment goes to the line’s end}

#include Statements


/* Hi, Mom. This is a comment that goes over 2 line. */int main() { std::cout << “Hello world!”; return 0; // This comment goes to the line’s end}

Nearly every C++ file begins with this directive May add more #include to include other

files Contents of included file usable as if it

were here Easy way to copy ideas across multiple

files Programs can use two types of #include

statements Include system file using #include <filename>

#include “filename” includes a file you wrote

Watch Me Pull a Rabbit



For now, automatically start each file with this line Details are unimportant – consider it

magic

Using Commands



More “magic”, but using has less important purpose Tells compiler we are lazy & save some

typing Two types of using statements to choose

from Specify single shortcut with using std::cout

using std; gives you a list of shortcuts to use

Unlike #include statements, using never required Do not worry about it – will not be using

them

main Function



that goes over 2 line. */ std::cout << “Hello world!”; return 0; // This comment goes to the line’s end

}

All C++ programs contain function called main Tells computer where to start running

program Code inside the braces will be what is

executed For the moment, consider this more “magic”

main Function

#include <iosteam>using std::cout;


that goes over 2 line. */ std::cout << “Hello world!”; return 0; // This comment goes to the line’s end

}

All C++ programs contain function called main Tells computer where to start running

program Code inside the braces will be what is

executed For the moment, consider this more “magic”

Comments

Vital for writing and maintaining any program Not required to run program - only for

human eyes Computer simply ignores anything in a

comment Use to describe code in simple English

Sie konnen auch auf Deutsch screiben o U c%d wrte n txt msg

Should be used liberally I add comments where cannot see what

code does Impossible to have too many comments, if

readable

Comments in C++

Double slash comments continue to line’s enda = a – 4; // Hi, Mom!// This entire line is a comment!

/* … */ comments can be on one or more linesa = a - /* Hi, Mom! */ 4;/* This comment takes an entire line. *//* This is a really long comment that * goes on to multiple lines. The stars on * lines 2 and on are optional, but * makes things easier to read. */

Pre-processor Directives

Code “pre-processed” before compilation No need to request it --- automatically

occurs Easier-to-read code results from this

process Just like using comments -- notice a recurring

theme? Pre-processor directives start with #

One directive per line & nothing else on the line

Directives should not span multiple lines

Symbolic Constants

Directive can be used to name a constant Any/all lines BELOW directive can use this

constant Pre-processor replaces name with value

Compiler sees value as if that were written there

When reading the code, programmer sees name

Makes code much easier to read, write, debug

Names traditionally in all CAPITAL letters THIS IS NOT REQUIRED, but common

convention

What You Write And Work With#define PI 3.1415962#define AVOGADRO 6.022E23 #define MY_NAME “Matthew Hertz”#define DUMB_EXAMPLE MY_NAMEdouble area = PI * (r * r);cout << MY_NAME;cout << DUMB_EXAMPLE;

What The Compiler Sees

#define PI 3.1415962#define AVOGADRO 6.022E23 #define MY_NAME “Matthew Hertz”#define DUMB_EXAMPLE MY_NAMEdouble area = PI * (r * r);cout << MY_NAME;cout << DUMB_EXAMPLE;


#define AVOGADRO 6.022E23 #define MY_NAME “Matthew Hertz”#define DUMB_EXAMPLE MY_NAMEdouble area = 3.1415962 * (r * r);cout << MY_NAME;cout << DUMB_EXAMPLE;


#define MY_NAME “Matthew Hertz”#define DUMB_EXAMPLE MY_NAMEdouble area = 3.1415962 * (r * r);cout << MY_NAME;cout << DUMB_EXAMPLE;


#define DUMB_EXAMPLE “Matthew Hertz”double area = 3.1415962 * (r * r);cout << “Matthew Hertz”;cout << DUMB_EXAMPLE;


double area = 3.1415962 * (r * r);cout << “Matthew Hertz”;cout << “Matthew Hertz”;

Variables

Variable names location to store data Memory location's initial value is unknown Assignments update memory location with

new value Memory location updated by assignment

ONLY When variable is used in program…

…uses current value at that memory location

Just about everything (interesting) uses variables

Variable Declarations

Variables must be declared before can be used Way of getting computer to make space for

variable States how to interpret memory in future

uses Allows the compiler to check if uses are

legal Declarations must include two pieces:

Each variable must have legal, unique name

Type of data that the variable stores

Variable Names

Begin with letter or underscore (_) Then use any letters, numbers, or

underscore C++ case-sensitive when naming

variables Will treat as different Mass, mass, & masS

Unique name* needed for each variable Computer wouldn't know which of 1,000 bobs to use

Reserved words are… reserved and can't be used Includes all type names on p. 83 of book void, unsigned, class also reserved words

Variable Name Conventions

Usually names begin with lowercase letter Helps clarify variables & symbolic constants

Provide good idea of what variable stores Split multiple uses into multiple variables

Some things always make for bad names tmp, b, l (lowercase letter L) Anything would not say to parents and/or

priest

Data Types

Each variable also has data type How program treats variable’s value

defined by this Single true or false value held by bool C/C++ defines 7 numeric data types

Integer types: short, int, long, long long Decimal types: float, double, long double Ranges for each type is not really

standardized Non-negative versions using unsigned

______ char data type can hold a character

Representing Text

Most computers you find follow ASCII standard American Standard Code for Information

Interchange 256 (= 28) possible characters in extended

definition Since computers are stupid, need to set

fixed size Only use 0s & 1s within computer – all

it knows Number still stored, but character is

displayed For number 97, a is printed Prints & for number 38 For number 55, 7 is printed

ASCII Table

There Is No Character

For computer, there are no characters Add to actual number just like normal

addition: ’M’ + 3 = 77 + 3 = 80 (’P’) ’0’ + 5 = 48 + 5 = 53 (’5’) 9 + ’1’ = 49 + 9 = 58 (’:’) ’1’+’0’ = 49 + 48= 97 (’a’)

Can also use to subtract, divide, any other operation

Writing Variable Declarations Single variable declared as: type name;double goodNameExample;short bad;

Can also declare multiple variables at once:int i, j;long double k, l, m, n, o, p;float thisIsAReallyLongName, thisIsAnotherLongName;

Writing Variable Declarations Could also specify initial value for

variable Variable, constant, literal, or expression can

be usedint i = 0.0;long j = -1;long double k = -0.000232847812;long l = j, many, minusJ = -j;char c = ‘i’;char newLine = ‘\n’;char tab = ‘\t’;

Constants

Constants very similar to variables Must be declared with a data type and

unique name const data_type var_name declares

variable Value of constant fixed when declared,

however Variables & constants treated and used

similarly

Your Turn

Get in groups & work on following activity

For Next Lecture

Read sections 5.1 – 5.4 & 5.6, 6.1 – 6.6 for Tues. What is this cout thing, anyway? Can we read in input from the keyboard? What operations exist for us to use with

variables? What do we mean by order of operations?

Week #1 weekly assignment due Tuesday Problems available on Angel – covered 1st

two already If problem takes more than 10 minutes,

TALK TO ME!

lecture 2: programming basics & variables

Documents