copyright 2001 oxford consulting, ltd1 january 2001 - 1 - building blocks overview in this lesson we...

Copyright 2001 Oxford Consulting, Ltd

1 January 2001

- 1 -

Building BlocksBuilding Blocks

Overview

In this lesson

• We will study the basic building blocks of a C++ program

• Explore data types that are part of the C++ language

• Look at basic arithmetic operators

• Begin our study of functions

• We will write some functions

To use data the user can enter into our

program

Return computed results


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Fundamental Data

Identifiers in C++

The name of object or function in C++ is called an identifier

Gives us means to refer to an entity in program

Such an entity may be a Variable Function


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Identifiers

Any combination of symbols can be used as an identifier, but….

The C++ standard establishes some restrictions

An identifier is case-sensitive

The first character of an identifier must be an alphabetic character or an underscore

Identifiers cannot be a C++ keyword

Identifiers have no length limit

An identifier is case-sensitive

The first character of an identifier must be an alphabetic character or an underscore

Identifiers cannot be a C++ keyword

Identifiers have no length limit


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IdentifiersSimple Variables

A variable is an object we use to hold data; it’s also an identifier

It has a name

The name let’s us refer to it in our program

It has a type

Tells us how big the variable is

Types are kind of like barrels

We have a number of different types or sizes of barrels

1, 2, 5, 10, 50 gallon containers

Should be immediately obvious

Putting contents of a 50 gal barrel into a 1 gal barrel is problem


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Identifiers

Intrinsic Types

Look around real world and we see we have a number of

different units we measure by….

– Inches, feet, yards, miles

– Centimeters, meters, kilometers

– Gram, kilograms, etc.

These are standards; They are intrinsic units of measure


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Identifiers

Intrinsic Types

C++ does same thing…just not with barrels

We have number of standard numeric types to hold stuff

These are predefined variables of different sizes

Such numeric types are called the intrinsic types,

The intrinsic types are classified into two groups

Integer Types

Floating Point Types


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Identifiers

Integer Types

Integer types are whole numbers ….They have no fractional part

25, -6, 100, 83, -972….

The C++ language standard defines the following integer types

char

short

int

long

bool

char

short

int

long

bool


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Identifiers

Integer Types

May be signed or unsigned … By default all are signed except

bool

A signed integer can be either positive or negative – Unsigned integer can only be positive

Signed Integerssigned int aNumber = -25;

or

int aNumber = -25;

Unsigned Integersunsigned int aNumber = 15;


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Identifierschar Integer Type

We represent characters by assigning a value to a char

char x = ‘A’; // Preferred

char y = 65; // Assigning numeric ASCII value

We denote a char type by enclosing a character in single quotes

This line of code will display the letter M on the screen.

cout << 'M' << endl;


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When I Say 0….

There is difference between 0 and '0'

0 is integer zero…that is, all bits are 0

A char integer with a value of zero is often referred to as a

null character

On the other hand the ASCII '0' has a value of 48


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Identifiersbool Integer Type

bool integer type can contain only two values…..

zero (false) or one (true)

To express conditions for success or failure of some test

We might write

bool pass = true;

bool fail = false;


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How Big is Big…The Size of Integer Types

Each of the integer types requires different amount of memory to

store its value

• The smaller the size of the variable

…..Fewer bits allocated to store it

…..Smaller the value it can hold

• Sizes of integer types varies by computer and operating system


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How Big is Big…The Size of Integer Types

#include <iostream>

using namespace std;

int main(void)

{

// checking sizes

cout << "A char is " << sizeof(char) << " byte" << endl;

cout << "A short is " << sizeof(short) << " bytes " << endl;

cout << "A int is " << sizeof(int) << " bytes" << endl;

cout << "A long is " << sizeof(long) << " bytes" << endl;

cout << "A bool is " << sizeof(bool) << " byte" << endl;

return 0;

}

#include <iostream>


int main(void)

{

// checking sizes

cout << "A char is " << sizeof(char) << " byte" << endl;

cout << "A short is " << sizeof(short) << " bytes " << endl;

cout << "A int is " << sizeof(int) << " bytes" << endl;

cout << "A long is " << sizeof(long) << " bytes" << endl;

cout << "A bool is " << sizeof(bool) << " byte" << endl;

return 0;

}

A char is 1 byte

A short is 2 bytes

A int is 4 bytes

A long is 4 bytes


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How Big is Big…The Size of Integer Types#include <iostream>

#include <limits>


int main(void)

{

cout << CHAR_MAX << endl; //displays char maximum

cout << CHAR_MIN << endl; //displays char minimum

cout << SHRT_MAX << endl; //displays short maximum

cout << SHRT_MIN << endl; //displays short minimum

cout << INT_MAX << endl //displays int maximum

cout << INT_MIN << endl; //displays int minimum

cout << LONG_MAX << endl; //displays long maximum

cout << LONG_MIN << endl; //displays long minimum

return 0;

}

#include <iostream>

#include <limits>


int main(void)

{

cout << CHAR_MAX << endl; //displays char maximum

cout << CHAR_MIN << endl; //displays char minimum

cout << SHRT_MAX << endl; //displays short maximum

cout << SHRT_MIN << endl; //displays short minimum

cout << INT_MAX << endl //displays int maximum

cout << INT_MIN << endl; //displays int minimum

cout << LONG_MAX << endl; //displays long maximum

cout << LONG_MIN << endl; //displays long minimum

return 0;

}

127

-128

32767

-32768

2147483647

-2147483648

2147483647

-2147483648

127

-128

32767

-32768

2147483647

-2147483648

2147483647

-2147483648


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With an integer type, the size of number we can express is

determined by number of bits in integer

Early PCs had integers containing 16 bits which meant that the

largest integer number that could be expressed was 65,536

Clearly we need to represent large numbers in a computer….

...Have to keep track of national debt after all

To do so we use different data type called floating point type


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Floating Point TypesConsider the number 3500….

We can easily rewrite this as 0.35 x 10000

Next we rewrite 10000 as 10*10*10*10 or 104

Thus the original number becomes 0.35 x 104

We call the 0.35 the fractional part or mantissa and

The 104 the exponent part

When number expressed in such a format, we say we’re using a

floating-point format


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C++ language standard specifies two floating-point types

float

double

• Each of these types contains the same maximum exponent • Double has more significant figures to the right of the decimal

point

– There is even a long double -


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Floating Point TypesFloating-point constants by default are of size double.

If we write

float pi = 3.14159;

We get truncation warning

We can avoid the warning by directing the compiler to create

3.14159 as a float and not a double.

float pi = 3.14159f;

or

float pi = 3.14159F;


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The const Qualifier

Consider the two declarations and initializing values….

int legalPaperLength = 17;

int standardPaperLength = 11;

Now let these two variables be assigned alternate values…

legalPaperLength = 14;

standardPaperLength = 10;


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The const Qualifier

C++ language gives us the ability to make the contents of a variable

constant

We use the const qualifier when we define the variable

Thus, when we declare the variables and we write

const int legalPaperLength = 17;

const int standardPaperLength = 11;

If we now try…..problemlegalPaperLength = 14;

standardPaperLength = 10;


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Functions

Let’s now take first look at the other kind of C++ identifier

Function

A C++ program is simply collection of functions

Some functions are pre-defined

We call these library functions

Most functionsUser defined


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Functions

As we write larger programs...

Will need to write more functions

More sophisticated functions

We write such functions to decompose program into more manageable pieces


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Functions

We create a function by defining it

Defining a function involves providing

Function header

Function Body


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FunctionsFunction Header

Specifies

Function name

Return type

Parenthesized parameter list


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Functions

Function Header

Function Name

Each function has a Name that is used to identify the function

The name should be descriptive of what the function does


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FunctionsFunction Header

Argument or Parameter List Arguments enclosed in parentheses Appear after the function name Separated by commas

Parentheses and the arguments

Called the argument list

Signature of the function Number, type, and order of arguments

Called the signature


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Functions

Function Header

Return Type

Return data from a function using a C++ return

statement

When a value is returned from a function using the return statement the function is said to have a return value

Kind of data returned called the return type.


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Functions

Function Body

Series of C++ instructions

Enclosed in curly braces

These express the function body

This is where the real work gets

done

Thus we have…


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Functions

returnType functionName ( arg0, arg1…argn-1 )

{

body

}

int multiply(int first, int second)

{

// this is the function body

}

returnType functionName ( arg0, arg1…argn-1 )

{

body

}


{

// this is the function body

}

Function Body


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FunctionsUsing a Function

Using a function is called

Executing

Evaluating

Invoking

Calling A function is executed

By performing a function call The function performing the function call

Is the calling function The function being executed

Is the called function


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Functions

In C++ all functions created equal…..

…..Any function can call any other function

Recall the simple program

int main(void)

{

// statements to execute go here

return 0;

}


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Functions

Let’s consider the multiply function we described above

We can write the function body such that

It is able to multiply the first and second argument

Return the product

We might ask... How do we call the function? How do we pass in the numbers to be multiplied? How do we use the product that is returned?


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Functions

#include <iostream>


int multiply(length, width); // function prototype

int main()

{

// declare some variables

int length = 10;

int width = 20;

int area;

area = multiply(length, width); // the function call

cout << area << endl; // displays 200

return 0;

}

#include <iostream>


int multiply(length, width); // function prototype

int main()

{

// declare some variables

int length = 10;

int width = 20;

int area;

area = multiply(length, width); // the function call

cout << area << endl; // displays 200

return 0;

}


{

int answer;

answer = first * second;

return answer;

}


{

int answer;

answer = first * second;

return answer;

}


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Functions

Function PrototypesIf we look back at the example program….

We see line near top of the program

#include <iostream>


int multiply(length, width);

The line that looks like the function header is important

Called function prototype

Functions need to be known before they can be used


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Functions

You might ask why we need this ????

Doesn’t the function header provide same information

Let’s see what’s going on here…..

When compiler encounters a function

It needs to know how to process it

It needs the information contained in header

To keep compiler happy

It’s sufficient to declare the function

If declaration not present we get a compile error

We declare a function by listing

return type function name (parameters)


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FunctionsNesting Functions

When one function used inside a second function

It’s called nesting

Now, a good question

How deeply can we nest functions????

Accompanying figure shows

Functions nested 4 deep

myF0()

myF1()

myF2()

myF3()


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FunctionsHow deeply can we nest functions????

Our question has a relative answer…..

We know the compiler

Makes copies of the variables it uses for arguments

Destroys the copies when the function completes

Seems reasonable that all copies hang around (on the stack)

Until the most deeply nested function call completes

When we run out of the stack memory our program will crash

Amount of stack memory varies with operating systems

Usually adjustable if needed


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Functions

Return ValueIn our study of functions we’ve observed the prototype

specifies

return type

We now ask question,

Do all functions have return value?????

The answer is no

void displayAnswer(int answer)

{

cout << "The answer is: " << answer << endl;

return; // this return is optional but is included // for clarity and completeness

}

void displayAnswer(int answer)

{

cout << "The answer is: " << answer << endl;

return; // this return is optional but is included // for clarity and completeness

}


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Functions

Now we use displayAnswer() in our example C++ program:

#include <iostream>using namespace std;int multiply(length, width);int main(){

// declare some variablesint length = 10;int width = 20;int area;

area = multiply(length, width); // the function calldisplayAnswer(area) // displays: The answer is 200return 0;

}

#include <iostream>using namespace std;int multiply(length, width);int main(){

// declare some variablesint length = 10;int width = 20;int area;

area = multiply(length, width); // the function calldisplayAnswer(area) // displays: The answer is 200return 0;

}


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Functions

Library FunctionsIn addition to our own functions….

….Many functions we will use are in libraries

A library is pre-compiled code and usually comes with your

compiler

To use a library function we include the proper header file

The header file contains the function prototype

This satisfies the compiler


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Arithmetic Operators

C++ uses operators to perform arithmetic operations on

variables.

Operators are the same for both integer and floating-point

Basic C++ operators are:

+ add

- subtract

/ divide

* multiply

…and they work as you would expect


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Operator Precedence

Let’s declare some variables…. e variablesint a = 20;

int b = 25;

int c;

Then write

c = a * 2/b + 15;

However, if we include these four lines of code in a program

Then compile and run it….

We will print the number 16 will appear

Why did that happen?

Variable c is

a times 2

divided by b

plus 15

Which is really 40 divided by 40

We expect the variable c to be 1

Variable c is

a times 2

divided by b

plus 15

Which is really 40 divided by 40

We expect the variable c to be 1


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Arithmetic OperatorsOperator Precedence

The answer lies in a concept we call operator precedence

Operators in C++ are evaluated in a specific order

Based upon precedence …..

For this example the compiler will

Perform division before addition

Perform multiplication before division


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Operator Precedence

In the light of precedence

1. a is multiplied by 2

Because multiplication comes before division or addition

This is 20 times 2 which is 40.

2. Next 40 is divided by b

Because division comes before addition

This is 40 divided by 25 which is 1.6

3. Finally, 15 is added to 1

To give 16


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Operator Precedence

If we wish evaluation to proceed in different order, we

can over

ride the precedence using parentheses

To force b plus 15 to be done before the division….

….We enclose those terms in parentheses

c = a * 2/ (b + 15);

Doing this changes evaluation order because the grouping

parentheses operator comes before any arithmetic operator


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Operator AssociativityNow we ask….

If precedence determines which operator is applied first,

What happens when all of the operators in a line of code

Have the same precedence?????

a + b – c

Does the compiler evaluate a + b or b – c first?

The answer is associativity subtraction

According to the C++ Operator Precedence and Associativity table

The associatively of addition and subtraction is Left to Right


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Arithmetic OperatorsInteger Division

For our example the answer will be 1. Why?????

Integers do not have fractional parts

Because the two operands are integers….

The compiler expresses result (1.6) as an integer

Which is 1 since 0.6 can't be expressed as integer

int x = 40;

int y = 25;

x = x / y;

cout << x << endl

int x = 40;

int y = 25;

x = x / y;

cout << x << endl


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The Modulus Operator %

We’ve seen integer division gives us Whole number part Remainder part

…and the remainder part disappears

If we want the remainder portion we must use an operator

Called the modulus operator

Written as percent sign

%

Also called remainder operator


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The Modulus Operator %Let’s apply the mod operator to the following integer

int number = 15;

cout << number % 3 << endl; // prints 0 …3 divides 15

// 5 times with 0 remainder

cout << number % 5 << endl; // prints 0 …5 divides 15

// 3 times with 0 remainder

cout << number % 10; << endl; // prints 5 …10 divides 15

// 1 time with 5 remainder

cout << number % 2; << endl; // prints 1 …2 divides 15 7

// times with 1 remainder

copyright 2001 oxford consulting, ltd1 january 2001 - 1 - building blocks overview in this lesson we...

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