Computer Science 1620

C++ - Basics

#include <iostream> using namespace std;

int main() {

return 0;}

• A very basic C++ Program.

• When writing your first programs, always start with this template.

• The code that you should write should go here.

• The details of this template (what each component means) will become clear as the semester progresses.

coutconsole output

sends data to the current output stream for us, this will typically mean the screen this can be re-routed to other output devices if

necessarywhen you wish to display something to the

screen, use the following syntax:

cout << a valid C++ expression

C++ Expressionan expression in C++ is an entity that

represents a value this value can take on many typeswe will look at one type of expressions first

string literal

String Literala string literal is a sequence of charactersenclosed in quotation marksExamples:

"Hello""Computer Science 1620" ”Dolly Parton"

Back to cout to display a string literal to the screen,

include it on the right side of the << operator

Example:write a program that displays the text "Hello

world!" on the computer screen.

#include <iostream> using namespace std;

int main() {

cout << "Hello World!"; cout << endl;

return 0;}

String literal

Notice the semicolon at the end of each lineall of your C++ constructs will end in a

semicolon (unless otherwise instructed) indicates the end of an instruction

What about the second cout command?cout << endl;

endl causes the data to be flushed from the buffer (explained in class), and moves the input to the next line

your output should always include a call to endl (at some point)

cout concatenation instead of having two separate cout

statements, you can include them on the same line

#include <iostream> using namespace std;

int main() { cout << "Hello World!" << endl;

return 0;}

#include <iostream> using namespace std;

int main() { cout << "Hello " << "World!" << endl;

return 0;}

Example: Write a program that writes your name and address to the screen:

#include <iostream> using namespace std;

int main() { cout << "Robert Benkoczi" << endl; cout << "123 Sunset Blvd" << endl; cout << "Hollywood, CA" << endl; cout << "90210" << endl;

return 0;}

applepie $ g++ -o print-adr print-adr.cc applepie $ ./print-adr Robert Benkoczi123 Sunset BlvdHollywood, CA90210applepie $

Recap: structure of a C++ program

the first 2 lines are almost always included in a C++ program. every program begins with “main ( )”. main begins with { and ends with } the brackets ( ) after main are required. program starts and ends in “main”. return 0 is put right before the closing } statements always end with a semicolon. Anything preceded with // is a comment and the compiler ignores it.

#include <iostream>#include <iostream>using namespace std;using namespace std;int main( )int main( ){ { statement 1;statement 1;

statement 2;statement 2;return 0;return 0;

} // end of program} // end of program

Other data types

C++ Data Typessimplestructured (struct, class)pointers function

we will deal with these later

Other data types

C++ Data Types four categories of simple data

integer whole numbers, no fractional part

floating point real numbers

enumerationboolean

Integer types a number without a decimal part

integers: 10, -24, 5800, -9600, etc…

non-integers 14.5, -24.6, 5800.0, -8 x 106

How are integers written in C++? in the simplest case, exactly as you would expect no spaces or punctuation (commas, dollar signs, etc)

Note that a number in C++ is an expressionhence, the number 34 is an expression

typically called an integer literal the value of this expression is 34

because it is an expression, it can be used wherever an expression is permitted

eg. as data to cout

Write a program that displays your name on the first line, and age on the second line. Display your name as a string, and your age as an integer.

#include <iostream> using namespace std;

int main() {

return 0;}

Integer types there are actually several flavours of "integer" in C++

by default, all integer literals are ints we will defer discussion about the others until we take

variables

* compiler dependent

Type Range Size

char -128 .. 127* 1 byte

short -32768 .. 32767* 2 bytes

int -2147483648 … 2147483647* 4 bytes

long -2147483648 … 2147483647* 4 bytes

Internal vs source code representations

Type:used to specify the internal representation

of a value (or expression). EX: how is that value stored in the computer memory.

Source code representation:how do we write a literal in the source code

Representation of integers

Representing numbers: roman: I, II, III, IV, V, VI, VII, VIIII, IX, Xarabic: coins with face value 1, 10, 100, 1000 etc

Base 2 numbering (face value 1, 2, 4, 8...)13 = 10 + 313 = 8 + 4 + 1 = 1101 (meaning 1 x 8, 1 x 4, 0 x 2,

1 x 1)

Representation of integers

Representing numbers: roman: I, II, III, IV, V, VI, VII, VIIII, IX, Xarabic: coins with face value 1, 10, 100, 1000 etc

Base 2 numbering (face value 1, 2, 4, 8...)13 = 10 + 313 = 8 + 4 + 1 = 1101 (meaning 1 x 8, 1 x 4, 0 x 2,

1 x 1)

Addition is easy with arabic numerals!bits

Representation of integers

char (8 bits or 1 byte)0 1 1 1 1 1 1 1 = +127

int, long - same idea, more bits.

represents the sign (+/-)

Representation of integers

negative integers1 0 0 0 0 0 0 0 = -0 (?)

This one’s complement representation. Not nice to have negative 0!

We would like to add + and - integers using the same procedure as for adding + integers.

represents the sign (+/-)

Representation of integers

two’s complement representation1 ? ? ? ? ? ? ? = -x

Goal: x + (-x) = x - x = 0 = 0 0 0 0 0 0 0 0

represents the sign (+/-)

Unsigned integers

Use when there is no need to represent negative integers. We can represent more positive integers.

Type Range Size

unsigned char

0 .. 255* 1 byte

unsigned short

0 .. 65536* 2 bytes

unsigned int

0 ... 4 294 967 295* 4 bytes

unsigned long

0 ... 4 294 967 295* 4 bytes

Floating Point Numbers a number with a decimal part

floating point numbers: 10.8, -24.8372, 5800.0, etc…

non-fps 14, 28, 96, -49

How are fp numbers written in C++? (source code representation) in the simplest case, exactly as you would expect no spaces or punctuation (commas, dollar signs, etc) scientific notation:

<mantissa> E <exponent> = <mantissa> 10<exponent>

Write a program that displays your name on the first line, age on the second line, and bank account balance on the 3rd.

#include <iostream> using namespace std;

int main() {

return 0;}

Floating Point types there are actually several flavours of fps in C++

by default, all floating point literals are doubles we will defer discussion about the others until we take

variables

* compiler dependent

Type Range Size

float 1.17549e-38 ... 3.40282e+38 4 bytes

double 2.22507e-308 ... 1.79769e+308* 8 bytes

long double 3.3621e-4932 ... 1.18973e+4932* 10 bytes

Integers vs. Floating Pointwhy would you use a floating point instead

of an integer?when you are working with real numbers

why would you use an integer instead of a floating-point number?

1) Integers use less memory than doubles2) Integers are more precise than floats

more on this when we take variables

Why would you use either number type instead of a string? after all, could we not just say:

cout << "Car Price:" << endl;

cout << "32999" << endl;

two reasons 1) Cannot do arithmetic on a string 2) Strings typically require more space than the number.

1) Cannot do arithmetic on a string next class, we will perform arithmetic on numbers

cout << (32999 – 5000) << endl;

you cannot perform the same operation on the string representation

cout << ("32999" – "5000") << endl;

2) Strings typically require more space than a numberas mentioned, an int requires 4 bytes of

memorya string requires x+1 bytes, where x is the

number of characters in the string32999 requires 4 bytes to store"32999" requires 6 bytes to store

Exercise: Determine an appropriate data type (int, fp, string) for each of the following?1) The average height of the class2) The number of desks in the class3) The name of the class4) The distance from my office to the

classroom