Writing and Reading C++ Programs A programming language has syntax and semantics like any

natural language Syntax is the set of rules like spelling and grammar in natural languages English: syntax spelled, sentences start with subject followed by verb

C++: main spelled, programs start with main() followed by { Semantics is the meaning

English: water means H2O C++: int means integer, + means add

Approaches of learning programming languages Template based

Examine example programs and make analogies Like a child learns how to speak

First learn syntax and semantics, then start by writing small programs, ... Like learning a foreign language

Which one do you prefer? We will follow the second method

First C++ Program Hello world program

#include using namespace std;

/* traditional first program */

int main(){cout

Format of a C++ Program

#include using namespace std;

/* traditional first program */

int main(){

cout

Format of a C++ Program

#include statements make libraries of classes and functions available to the program Utility functions and tools that make the programmers life easier are defined in libraries

Helps programmers develop code independently in a standard way and reuse common operations

Compiler needs access to interface (definition), what the functions look like, but not to the implementation of those functions This is in the #included file e.g. #include

for input/output functions all programs that use standard C++ libraries should have

using namespace std;

Format of a C++ Program Comments make programs readable by humans (and by assistants!)

Easier maintenance Try to use natural language, do not repeat the code!

Bad examplearea = pi * r * r; /* area is pi*r*r */

Better examplearea = pi * r * r; /* calculate area */

Best examplearea = pi * r * r; /* calculate area of a circle

of radius r */ Two ways of commenting

Using // make the rest of the line commentarea = pi * r * r; // calculate area

Between /* and *//*

Calculate area of a circle of radius r*/area = pi * r * r;

Compiler disregards comments In VC++, comments are in green

Format of a C++ Program

Execution of the program begins with main

Each program must have a main function

Execution of C++ programs is organized as a

sequence of statements

Statements execute sequentially one after another statement 0, statement 1, , statement (n-1)

Branching, repetition are possible (we will see them later)

The main function returns a value to the operating

system or the environment in which it is executed

return 0

Why 0? Because 0 means no problems (errors)

encountered!

Format of a C++ Program

Each statement ends with a ; (semicolon)

except #include and function headers like main()

Each statement has optional line break after the ;int main(){// This is valid code toocout

Rules of C++

Now some syntax rules and definitions

ABC of C++

What is a literal?

Reserved words (keywords)

What is an identifier?

Variables and basic types

Symbols and compound symbols

Where to use blanks, line breaks?

Basic Input/Output

Literals Fixed (constant) values

They cannot be changed during programs execution

They can be output by cout

Different format for different types: String literals

Sequences of characters

Within double quotes (quotes are not part of the string)

Almost any character is fine (letters, digits, symbols)

"Hello world!" " 10 > 22 $&*%? "

Numeric literals Integer

3 454 -43 +34

Real

3.1415 +45.44 -54.6 1.2334e3

1.2334e3 is 1.2334 times 10 to the power 3 (scientific notation)

Identifiers Names of programmer defined elements in a program

Names of variables, functions and parameters

Examples:number1 valid

number_1 valid

mySum valid

my_sum_1 valid

1number not valid

Syntax (rules):1.Sequence of letters (a .. z, A ..Z), digits (0 ..9) underscore _

2.Cannot start with a digit or underscore

3.Case sensitive (number1 and Number1 are not the same)

Pick meaningful names to improve readability and understandability of your program (be consistent)

Hungarian notation

Reserved Words (Keywords)

Special and fixed meanings

built-in in C++ language

no need to have libraries to use them

You cannot use a reserved word as a user-defined identifier

Cannot be changed by programmer

int

return

Full list is Table 2.1 of the textbook

Full list also in MSDN:

http://msdn.microsoft.com/en-us/library/aa245310(VS.60).aspx

In MS VC++, reserved words are automatically blue

Variables and Types

Variables are used to store data values that can

change during the program

Input (cin) data is stored in variables

Results are stored in variables

Named memory locations of certain sizes

Must be defined before they can be used

Often initialized before use

Syntax:

type name; identifier

type name1, name2, , namek;

Common types:

int number1, age, sum;

string myName, last_name;

float area, distance;

number1 age

Memory

area

distance

myName

sum

last_name

Symbols

Non-digit and non-letter characters with special meanings

Mostly used as operators (some examples below, full list later)Symbol Meaning Example

+ addition, sign 12 + 2, +67

- subtraction, minus 37 5, -8

* multiplication 3 * 5 * number

/ division 5.2 / 1.5

% modulus/remainder 7 % 2

= assignment sum = x + 5;

Symbol Meaning Example

/* comment start /* calculates

*/ comment end area */

stream input cin >> number;

== equality comparison number == 0

Compound symbols (two consecutive symbols one meaning),

examples below, full list later

Arithmetic Operations

Operators: + - * / %

Operands: values that operator combines

variables or literals

Combination of operators and operands is called expression

Syntax and semantics for arithmetic operations:

AdditionSubtraction

Multiplication Division Modulus

23 + 4 23 * 4 21 / 4 is 5 21 / 4 is 5

x + y x * 3.0 21 / 4.0 is5.25

18 % 2 is 0

d 14.0 + 23 d * 23.1 * 4 x / 4 x % 4

5 - 3 + 2 5 3 * 2 x / y x % y

See Figure 3.4 in the book.

Assignment Operator

Stores a new value in a variable

variable = expression;

The value of expression becomes

the value of variable

int number;

number = 40;

number = 40 + 5;

string name;

name = "Gulsen";

number * 4 = 56; wrong syntax

Previous value of variable is lost

Be careful about the types of left and right hand sides

they must match

compiler may or may not warn you int a = 32.6;

Memory

number

45

name

name

Gulsen

value

Example Program Write a program to calculate the area of a circle

program first input a name and print a greeting input the radius calculate and display area

identify literals, identifiers, keywords, symbols, variables and expressions

#include #include using namespace std;

// area calculation program

int main(){int radius;float area;string myname;cout > myname;cout

Issues with the Example Program

What happens if the user enters a real number for

radius?

wrong result

solution: real radius

Can we combine?cout

Where to use Blanks (Newline) You must have at least one blank

between two words (identifiers or keywords) e.g. int number;

between a word and numeric literal e.g. return 0;

You cannot have a blank within a word (e.g. float) within a compound symbol (e.g.

Stream Output

Output is necessary for our programs

Standard output stream cout is the monitor (read see-out)

cout is implemented in the iostream library

Output is sent to stream by the

Stream Input Input is also necessary for our programs

Standard input stream cin is the keyboard (read see-in)

cin is also implemented in the iostream library

You can input only to variables

Input is read from the stream by the >> operatorcin >> number;

More than one input could be read from the streamcin >> variable1 >> variable2 >> variable3 ;

Data will be read into the variables in the same order they are in the cin statement

int a, b, anynumber;

cin >> b >> anynumber >> a;

first the value for b, then the value for anynumber, then the value of a must be entered by the user using the keyboard

Stream Input You have to have at least one blank between any two inputentry

Multiple blanks are OK

You may input values at several lines for a single cin statement

You cannot display something using cin statement

Type match between variable and the corresponding input value

If mismatch then the input entry fails for the rest of the program

But the values read up to that point are kept in the variables

Stream Input Example showing the

operation

Data Types string

used it in previous lectures

more technically, string is a class

char for single character

digits, letters, symbols

uses up one byte

range 0 ... 255

why? one byte (8 bits) can store 28 = 256 different values.

stores the code of the character

e.g. 65 for A

character arithmetic is possible (will see later)

char literals are in single quotes (strings are in double quotes ")

'z' 'T' '4' '&'

bool

boolean (will see later)

Numeric Types

to represent integer and real numbers

int

integer numbers

no infinity in computers

limited range

2 or 4 bytes (16 or 32 bits) depending on the computer and

compiler you use

in our case: 4 bytes (32 bits)

integer range:

32,768 ... 32,767 for 16-bit computers

why?

2,147,483,648 ... 2,147,483,647 for 32-bit computers

why?

Numeric Types (contd)

short int (or just short ) always 16-bit integer

long int (or just long ) always 32-bit integer

signed versus unsigned integers you can put signed or unsigned keywords before the type

we discussed signed integers signed is default

unsigned integers use the same amount of bits but ranges are different 16-bit: 0 ... 65,535 (216 1) 32-bit: 0 ... 4,294,967,295 (232 1)

Numeric Types (contd)

Real numbers in C++

Real literals 3.14159 -2.5 5.43e21

Real data types (their difference is in precision) float

consumes 4 bytes

Range: 0 U [-1.175494351e38 ... -3.402823466e+38]

U [1.175494351e38 ... 3.402823466e+38]

Tapestry does not like float

double consumes 8 bytes

Range: 0 U [-2.2250738585072014e308 ... -1.7976931348623158e+308]

U [2.2250738585072014e308 ... 1.7976931348623158e+308]

Standard but a bit complex representation

see floating point representation item in MSDN Library index: http://msdn.microsoft.com/en-us/library/0b34tf65.aspx

More on C++ types

Check out these items in MSDN Library Index

Fundamental types

more on C++ types

LIMITS.H header file (Microsoft Visual Studio\VC98\Include)

limits of integer and char types

MSDN help on Integer Limits

floating limits (FLOAT.H)

limits for the floating points numbers (float, double)

MSDN help on Floating Limits

floating point representation

if you are interested in to learn how the real numbers are

represented in computers

MSDN help

Integer vs. Real

Real values can be assigned to Integer variables, but this is not recommended since we loose precision

int a;double r;r = 125.879;a = r;

What is the value of a? 125

Real value is truncated before storing in an integer variable

Avoid doing this

VS 2008 Compiler warns you but does not give error

Be careful when passing arguments to parameters as well passing an integer argument to a double parameter causes the same precision problem

Overflow

See daysecs.cpp

Overflow occurs when the result of an integer expression is outside the limits

Run the program with 365 days

result: 31536000 seconds correct result and output

14500 days result: 1252800000 seconds correct result and output

25129 days result: -2123821696 seconds incorrect result and output due to overflow

65400 days result: 1355592704 seconds incorrect result and output due to overflow

Arithmetic Operations

Operators: + - * / %

Operands: values that operator combines

variables or literals

Combination of operators and operands is called expression

Syntax and semantics for arithmetic operations:

AdditionSubtraction

Multiplication Division Modulus

23 + 4 23 * 4 21 / 4 is 5 21 / 4 is 5

x + y x * 3.0 21 / 4.0 is

5.25

18 % 2 is 0

d 14.0 + 23 d * 23.1 * 4 x / 4 x % 4

5 - 3 + 2 5 3 * 2 x / y x % y

Arithmetic Operations (contd)

Mixed type expressions

what if one operator is int other is double?

integer is converted into double before operation

5.0 * 8 is 40.0

5 / 10 is 0 (integer division)

5.0 / 10 is 0.5 (real division)

10 8 is 2 (integer)

10 8.0 is 2.0 (double)

Expressions with several operators

You can use parentheses in expressions to group them Open ( and close ) parentheses should match

Rule 1: Parenthesized sub-expressions are evaluated first inside to out

Rule 2: Within an expression/subexpression if there are several operators, use operator precedence, evaluate * / % before + -

Rule 3: If the operators are in the same expression/subexpression and at the same precedence level, then associativity rule applies evaluate operators from left-to-right

Examples(5 - 3 * (7 - 3)) * 8 is -56

10 / 2 * 6 / 2 + (5 - 3 * (2 - 1)) is 17

Expressions with several operators

Are the following expressions equivalent?(40 32) * 5 / 9

(40 32) * (5 / 9)

NO, first one is 4, second one is 0

What about this?(40 32.0) * 5 / 9

Operations are double operations. Result is 4.44444

Are these operators sufficient?

how to calculate square root?

Later well study functions like sqrt, cos, sin, pow,

For complicated mathematical operations that you cannot

easily do using basic operators

Accessible using #include (or )

Integer vs. Real (More on

Precision) What is the difference between red and blue parts in the

following program (fahrcels.cpp)?

red: integer arithmetic (low precision)

blue: real arithmetic (high precision)

int main(){

int ifahr;double dfahr;

cout > ifahr;cout

More on Assignment operator (4.1 & 4.3.4)

Assignment operator is =

to store values in variables

variable = expression;

first the right hand side expression is evaluated using the current values

then the evaluated expression is stored in variable

Types should be compatible, otherwise

a syntax error may occur (e.g. string variable, integer expression), or

precision is lost (e.g. integer variable, real expression)

Example: what is the value of a after the assignment?

int a, b;

b = 25; a = 8;

a = b 3 * a + 2;

Answer: 3

A rule: Right hand side expression is evaluated before the assignment operator is executed.

If you use the left hand side variable in the right hand side expression as well, then the current value is used in the expression.

See Program 4.1 in textbook.

More on Assignment operator (4.1 & 4.3.4)

Assigning single expression to several variablesvariable1 = variable2 = variable3 = ... variablen = expression;

all variables are assigned the same value of expression

example:int x, y, z;

x = y = z = 5;

x, y and z contain 5

Arithmetic assignment operators+= -= *= /= %=

Combines arithmetic operation and assignment in one operator

variable += expression is the same as variable = variable + expression

Example: x += 1 is the same as x = x + 1

Same for -= *= /= and %=

x -= 1 x *= 3 x /= 2 and x %= 2