Medium Level C++

Medium Level C++ Structures, Function, Arrays and Pointers

Engineer Jokhio Sultan Salahuddin Kohistani

Lecturer, CSE, MUET Jamshoro

Structures

We have seen some primitive data types, like int, float

char etc. but C++ also offers some user defined data

types in shapes of structures.*

Structures are user defined data types, which are

combination of several primitive data types.

A structure is a collection of simple variables.

The variables are mostly of different types.

The data items in a structure are called the members of

the structure.

Engr. SDJK, CSE, MUET Jamshoro 2

Definition Syntax & Accessing Structures

struct name-of-struture{

datatype var-name;

datatype var-name;

datatype var-name;

….

};

Accessing:

With dot operator (.)

Structures can be declared and defined outside the main

function.


Structures Definition

Accessing a Structure variables:


Structures Cont.

Definition of a structure variable

notice that the format for defining a structure variable is

the same as that for defining a basic built-in data type

such as int:


Structures in memory


Combining all those //structures.cpp

#include<iostream>

using namespace std;

struct part //declare a structure

{

int modelnumber; //ID number of widget

int partnumber; //ID number of widget part

float cost; //cost of part

};


Combining all those //program is continued

int main()

{

part part1; //define a structure variable

part1.modelnumber = 6244;

part1.partnumber = 373;

part1.cost = 217.55F;

cout << “Model “ << part1.modelnumber;

cout << “, part “ << part1.partnumber;

cout << “, costs $” << part1.cost << endl;

return 0;

}


Output


Structure

All Structures have

their own variables


Alternative version of the program:

Assigning in a different way

// structures2.cpp

// shows initialization of structure

variables

#include <iostream>


struct part //specify a structure

{

int modelnumber; //ID number of widget

int partnumber; //ID number of widget part

float cost; //cost of part

};


//cont.

int main()

{

part part1 = { 6244, 373, 217.55F };

part part2; //define variable




part2 = part1; //assign first variable to second




return 0;

}


Functions

A function is the entity in a computer program which groups

the set of statements as a single unit, which when called,

perform some useful operation, like calculating the square of a

number, setting up spaces, asking user to enter something.

A function simply is a collection of statements.

The function could be called from any where of the program.

When the function is called, all the statements inside it are

executed.

Two types

User Defined

Library


Program (Prototyping/Declaration of the

function)

// functiondemo1.cpp

// demonstrates simple function

#include <iostream>


void starline(); //function

declaration

// (prototype)


Program (calling the function).

//Continued from above

int main()

{

starline(); //call to function

cout << "Students Percentage" << endl;


cout<<"12CE01 80"<< endl

<<"12CE02 85"<< endl

<<"12CE03 70"<< endl;


return 0;

}


Program (Function Definition)

// starline()

// function definition

void starline() //function declarator

{

for(int j=0; j<20; j++) //function body

cout << '*';

cout << endl;

}


Explanation

The program consists of two functions: main() and

starline(). You’ve already seen many programs that use

main() alone.

What other components are necessary to add a function

to the program?

There are three: the function declaration, the call to the

function, and the function definition.


The Function Declaration

Also called function prototyping.

Just as you can’t use the variable, before you declare it, Simply

you also can’t use a function without first declaring it.

Declaration is necessary, in case you are defining the function

after the main, but if you are defining the function before the

main function, then there is no any need of declaration, you

can directly define and call the function.

The above line is a typical declaration.

Function declaration is terminated with semicolon, this tells

the compiler that, the function will be used inside main, but

will be defined later on.

Sometimes referred as Signature of the function.


Calling the Function and Its Definition

The main calls the function three times, using the

following statement.

When called, the control is shifted to the function

definition, and all the statements inside the function are

executed.

The Function definition is the actually the collection of

statements that comprises itself.

The First line in the function definition is called the

function declarator, which is followed by the function

body.


Summary of the Function Components


Eliminating the declaration #include <iostream>


void starline()

{

for(int j=0; j<6; j++)

cout << ‘*’<<endl;

}

int main()

{


cout << “HELLO ” << endl;

starline();

return 0;

}


Arrays

As structures are combining different data type variables,

Arrays are entities which are providing feature of

grouping same data types as one single unit.

They are holding homogeneous (similar) type of data.

Can hold few as well as tens of thousands.

Items or members in structures are accessed through

their names with dot operator, but in Arrays we can

access members with their index number which is also an

element number, So accessing elements is easier in arrays.

Arrays can be single dimensional as well as

multidimensional.


Syntax for single dimensional array

Now this age array will have four elements, starting from age[0] …..

To age [3], total 4 elements. So, the index of first element is zero and

last element is one less than array’s size i.e. 3 = 4-1.


Arrays inside the memory

Array’s elements inside the memory

are placed sequentially.

The figure shows typical elements

placed inside the array named age[ ].

Now all elements are of integer data

type.


Accessing array elements

As Array Elements are sequential in nature, they

individually could be easily accessed with the use of loop.

For loop is better to use, as array size is fixed and almost

known in all cases.

So, we can access each element of an array using a for

loop, starting its counter variable from 0, to the last

element (1 less than array’s size). To access elements

inside age array of size 4, we will use following loop.

for (int i=0;i<4; i++) or for (int i=0; i<=3; i++)


Program

#include <iostream>


int main(){

int age[4]; //array 'age' of 4 ints

for(int j=0; j<4; j++) //get 4 ages

{

cout << "Enter an age number "<<j+1<<‘\n’;

cin >> age[j]; //access array element

}

for(int j=0; j<4; j++) //display 4 ages

cout << "You entered " << age[j] << endl;

return 0;

}


Explanation

We have used two for loops, one for input of the

elements, while other is for output of the same elements

on the screen.

As our Array’s size is 4, so our loop starts from 0 and

ends up with 3 (less than 4).

As j’s scope is only to first loop, we also can use same

name for counter variable inside second loop, so we have

to declare it once again.


Averaging the array elements #include <iostream>


int main(){

const int SIZE = 6; //size of array

double sales[SIZE]; //array of 6 variables

cout << "Enter widget sales for 6 days\n";

for(int j=0; j<SIZE; j++)cin >> sales[j];

double total = 0;

for(int j=0; j<SIZE; j++) total += sales[j];

double average = total / SIZE; // find average

cout << "Average = " << average << endl;

return 0;

} Engr. SDJK, CSE, MUET Jamshoro 28

Initializing Arrays: An alternative

int days_per_month[12]=

{31,28,31,30,31,30,31,31,30,31,30,31};

Now first element days_per_month [0] will contain 31 and

next will contain 28 and so on, so last element

days_per_month [11] will contain 31.

Similarly,


Multidimensional Arrays

Can be two dimensional array, three dimensional, and so

on.

Working with more than two dimensions is really hard

and time consuming.

A two dimensional array is like a two dimensional matrix.

So, a two dimensional array is an array of arrays.

const int DISTRICTS = 4;

const int MONTHS = 3;

double sales[DISTRICTS][MONTHS];


For every sales array, there would be 4 arrays, each array

capable of storing 3 elements.

To access we would use two for loops:

for(int i=0;i<DISTRICTS;i++){

for(int j=0;j<MONTHS;j++){

cin>>sales[i][j];

}


An Alternative Initialization

int sales[2][3]={ {1, 1, 4}, {5, 7, 80} };


Two – Dimensional Array in Memory

Two for loops

(nested)

Can be used to

Access both

dimensions


Adding two 3x3 Matrices

#include<iostream>

#include<iomanip>


int main(){

int matrixA[3][3];

int matrixB[3][3];

int result [3][3];

int i,j;

//continued


//Enter Matrix A

for(i=0;i<3;i++){

for(j=0;j<3;j++){

cout<<"Enter Matrix A Element number:row

"<<i<<" Column "<<j<<"\n“;cin>>matrixA[i][j];

}

}

//Enter Matrix B

for(i=0;i<3;i++){

for(j=0;j<3;j++){

cout<<"Enter Matrix B Element number:row

"<<i<<" Column "<<j<<"\n";cin>>matrixB[i][j];

}

}


//Calculate the sum in new Matrix in

show its elements on the screen

for(i=0;i<3;i++){

for(j=0;j<3;j++){

result[i][j]=matrixA[i][j]+matrixB[

i][j];

}

}

cout<<"*********************************

*****\n";


cout<<"Here is the Result below\n\n\n\n";

for(i=0;i<3;i++){

for(j=0;j<3;j++){

cout<<setw(5)<<result[i][j]<<setw(10)<<

" ";

}

cout<<endl;

}

return 0;

}


Addresses and Pointers

Every Byte in a computer memory has an address

assigned to it.

So, data is stored at different locations (bytes) of different

sequential addresses inside memory.

Addresses (in computing) are simply numbers (Mostly in

hexadecimal format).

When your program loads inside memory, it is assigned a

address or range of addresses inside RAM (memory).

Which means variables at functions start at some

particular address inside memory.


Addresses inside Memory

If var1 is int

2 Bytes

If var2 is char

1 Byte

If var3 is float

4 Bytes


The Address-of (&) Operator

Used to retrieve or fetch or find the address of a variable

inside memory.

(&) Ampersand sign is used in front of variable to find it’s

address.

Addresses can be printed used

cout<<&variable-name; //statement.


Program (Address-of operator)

#include <iostream>


int main()

{

int var1 = 11; //define and initialize

int var2 = 22; //three variables

int var3 = 33;

cout << &var1 << endl << &var2 << endl<<

&var3 << endl;

return 0;

}


Pictorial Explanation

Addresses appear in descending

Order.

Below is the sample output.


Pointers

Pointers are special type of variables to hold the addresses of variables inside memory.

A pointer variable has special format of definition.

We can-not store address in other variables than pointers.

Like

int a, b;

a=&b; //invalid, because address of b can’t be stored inside a, which is not a pointer variable.

So, Pointers are distinguished from conventional variables by use of Asterik (*) in front of the data-type or variable-name.


Declaring Pointers

The * sign shows that ptr is a pointer variable, which can

hold the address of an integer data-type variable.

Or in other words, ptr is a pointer to integer variable.

Other data-types can be used as following:

And so on.


Program


#include <iostream>


int main()

{

int var1 = 11; //two integer variables

int var2 = 22;

cout << &var1 << endl << &var2 << endl << endl;

int* ptr; //pointer to integers

ptr = &var1; //pointer points to var1

cout << ptr << endl; //print pointer value

ptr = &var2; //pointer points to var2

cout << ptr << endl; //print pointer value

return 0;

}

Explanation


ptr is a pointer variable, which now holds the address on

var1, both ptr and var1 have int data type.

Here is the sample output:

The End


Test#3


On 21 April, 2012, Saturday.

Assignment


Q#1. What is Data Processing; discuss the applications of computers in civil engineering. Discuss contributions of Charles Babbage?

Q#2. Convert following numbers from binary to decimal (i-ii-v) and from decimal to binary (iii-iv) respectively.

i) (100100111)2 ii) (101100011)2 iii) (4500)10

iv) (101100101)10 v) (10111010)2

Q#3: What is the output of the following lines of code?

1) int a = 5, b=2;

float z = a/b;

cout<<z;

II) What is the output the following lines of code?

bool condition1;

condition = 7/2>1;

cout<<condition;

Assignment cont.


Q#4. What is operator’s precedence? Discuss in detail.

Elaborate using the Tabular explanation.

Q#5. What is BIOS and POST? Discuss in detail.

Q#6: Survey computer market and find out, what is

specifications of most selling computer along with

peripherals. Model numbers, and different detailed

specifications along with input, output, storage devices.

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Medium Level C++