Arrays and library functions

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Arrays and Library Functions
Arrays: - An array is a collection of variables of the same type that are referenced by a common
name. It consists of contiguous memory locations.
Need for arrays:- For large applications or calculations say to find the average marks of 50
students if we use 50 different variables the job will be cumbersome and tedious and program
maintenance will be very difficult. But if we use array the remembering and managing these
variables will be easy.
To make the program complex –free and more understandable array is used.
Declaration of arrays:
Syntax:- data-type array-name[size];
For ex:- int A[10];
float B[20];
char C[30];
where data-type refers to any fundamental(or primitive or in-built) data types, array-name
will be any valid identifier name and size will be any number which indicates no. of elements
the array contains.
Types of Arrays:- Arrays are of two types:- (i) one-dimensional arrays and (ii) Twodimensional arrays. Both the arrays can be of numeric as well as character (or string) types.
(i) One-dimensional (or single dimensional or 1-D) arrays:- It is
types of elements referenced by a common name. The elements of the
subscripts or indices.
For eg. int A[5];
The above array will be having elements : A[0], A[1], A[2], A[4], A[5].
numbers which are within [ ] ) always starts with number 0 not 1 in
the locations of the elements within the array.

a collection of similar
are referred by their

Array subscripts ( the
C++. Subscripts are

Memory representation of 1-D array
Let us take the above example which is int A[5];

A[0]
Starting
address

A[1]
25

A[2]
-13

A[3]
44

A[4]
0

Location
10

value

Where A[0] is the first element, A[1] is the second element and so on. The last element (i.e. 10
here) always having location A[size-1]. Each element contains 2 bytes of memory.
The address of first element of the array i.e. &A[0] is called the base address of the array.
Note:- The name of the array (here A) is a pointer to its base address i.e. first element’s
address (i.e. &A[0]).
Size of the array in memory = data-type X size of the array
For the above array the memory occupied will be 2 X 5 = 10 bytes.
We can find it using C++ coding also
cout << sizeof(A); here sizeof is a operator which is used to find the size of any data
type, variable or derived data type in bytes and A is the array name.
Initialization of One-dimensional array (Numeric type):- There are two types of
initialization
(i)
Sized array initialization and
(ii)
unsized array initialization
(i) Sized array initialization :- It can be done during the program writing (i.e. before program
execution) or during the program execution (Using Loop).
For ex:-

int A[5] = {12, 13, 20, 5, 2};

Prepared By Sumit Kumar Gupta, PGT Computer Science

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float B[4] = { 3.4, 4.5, 6.2, 7.8};
This is sometimes called direct initialization.
code segment:
int A[5];
for( int i=0; i<5; i++)
cin >> A[i];
Here the values must be provided by the user during the execution of the program.
In the first case the values are actually assigned during the compilation time and in the second
case the values are assigned during the execution time by the user’s input.
(i) Unsized array initialization :- It can only be done in following ways:
int A[ ] = {2, 5, 17, 10, 12};
// No size is given within [ ]
char str[ ] = “Kendriya Vidyalaya”;
The compiler will automatically fixed the size of the array. Here the advantage is that the
number of elements can be increased or decreased without considering the size. It is more
flexible whenever there is a requirement of direct initialization or the values are known to the
user.

String as an array:- C++ does not string data types rather it implements string as onedimensional character arrays.
String is defined as a array of characters that is terminated by a null character ‘0’.
For ex:- char str[20] = “Kendriya Vidyalaya”;
It can be represented as

str[0]
K

Location in the array

str[8]
e

n

d

r

i

y

a

V

i

d

y

a

l

a

y

str[18]
a

0

The above array contains 18 characters , but it can contain maximum of 19 characters i.e. size –
1 characters and one space is reserved for null character. Here the length of the array is 18.
The position of null character is not taken for finding the length of the array.
(i) Two-dimensional (2-D) arrays:- A two-dimensional array is a multi one-dimensional
arrays. It consists of rows and columns i.e. it is in a matrix format.
For instance an array A[m][n] is an m by n table with m rows and n columns containing m X n
elements.
The no. of elements = no. of rows X no. of columns
One of the use of 2-D numeric array is matrix manipulation which is one of the important concept
of mathematics.

Declaration of 2-D array:
The general form of a two-dimensional array is
Syntax:- Data-type array-name [rows] [columns];
Where data-type is any base data type, array-name is any valid identifier name and rows, the
first index indicates the no. of rows and columns the second index, indicates the no. of columns.
For ex:- int Price [4] [5];
The array Price have 4 elements Price[0], Price[1],……., Price[3] which itself an int array with 5
elements. The individual elements of Price are referred to as Price[0][0], Price[0][1],…….,
Price[0][3], Price[1][0], Price[1][1] and so forth. The last element will be Price [3][4].

Memory Map Representation :Ex:-

int Price [4][5];


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Columns

0

1

2

3

n-1

4

0
1
Rows

m = rows, n = columns
2
3
Price [3][4]

Price [1] [1]

m-1

Size occupied by the above array in memory = data-type X rows X columns
= 2 X 4 X 5 = 40 bytes
C++ statement will be : cout << sizeof(Price);

Array of Strings:- The two-dimensional character array is known as array of strings. The size of
the first index (rows) is the number of strings and the size of the second index (columns) is the
maximum length of each string.
For ex:char days [7][11];
Declares an array of 7 strings each of which can hold maximum of 10 valid characters where 1
extra to take care of the null character ‘0’;

The above array of strings appears in memory as shown below:

(11)

0

(7)

0
1
2
3
4
5
6

M
T
W
T
F
S
S

1
O
U
E
H
R
A
U

2

3

4

N
E
D
U
I
T
N

D
S
N
R
D
U
D

A
D
E
S
A
R
A

5
Y
A
S
D
Y
D
Y

6
0
Y
D
A
0
A
0

7

8

0
A
Y

Y
0

Y

9

10

0

0

Array Initialization:- Like One-dimensional array two-dimensional array can be initialized in two
ways:(i) Sized 2-D array initialization
int SQ[3][2] = { 1, 1,
2, 4,
3, 9
};

int SQ[3][2] = {1,1, 2,4, 3,9};


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For Array of strings:
Char Months[12][4] = {“Jan”, “Feb”, “Mar”, “Apr”, “May”, “Jun”, “Jul”,
“Aug”, “Sep”, “Oct”, “Nov”, “Dec”};
(i) Unsized 2-D array initialization
int Cube[ ][2] = { 1, 1,
2, 8,
3, 27,
4, 64
};

-- rows should be left blank

Char Months[ ][4] = {“Jan”, “Feb”, “Mar”, “Apr”, “May”, “Jun”, “Jul”,
“Aug”, “Sep”, “Oct”, “Nov”, “Dec”};
The advantage is that one can increase the rows as and when required.
In C++ program nested loop is required for taking inputs for numeric type 2-D arrays
whereas generally single loop is used for taking inputs in character type 2-D arrays (i.e. for
array of strings).
For string input gets ( ) function (which is defined in stdio.h header file) is normally preferred
over cin>> operator since it can able to take the white space characters (tabs, spaces etc).
Code segment:

int Mat[4][5];
for (int i = 0; i < 4; i++)
{-- Nested loop
for (int j = 0; j < 5; j++)
cin >> Mat[i][j]; -- Here i indicates rows & j indicates

columns
char days [7][11];
for (int i = 0; i < 7; i++)
gets(days[i]);
//Q1. Write a program to display the multiplication of two matrices
#include<iostream.h>
#include<conio.h>
void main()
{
clrscr();
int A[50][50],B[50][50],C[50][50];
int r1,c1,r2,c2,i,j,k;
cout<<"nEnter the rows & columns for matrix A:";
cin>>r1>>c1;
cout<<"nEnter the rows & columns for matrix B:";
cin>>r2>>c2;
cout<<"nEnter the elements for matrix A:n";
for(i=0;i<r1;i++)
for(j=0;j<c1;j++)
{
cout<<"element"<<i<<","<<j<<":";
cin>>A[i][j];
}
cout<<"nEnter the elements for matrix B:n";
for(i=0;i<r2;i++)
for(j=0;j<c2;j++)
{
cout<<"element"<<i<<","<<j<<":";
cin>>B[i][j];


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}
if(c1!=r2)
{
cout<<"matrix multiplication is not possible!";
getch();
return;
}
else
cout<<"multiplication is possible!";
//Multiplication
for(i=0;i<r1;i++)
{
for(j=0;j<c2;j++)
{
C[i][j]=0;
for(k=0;k<r2;k++)
{
C[i][j]+=A[i][k]*B[k][j];
}
}
}
cout<<"nMatrix A:n";
for(i=0;i<r1;i++)
{
cout<<"n";
for(j=0;j<c1;j++)
cout<<A[i][j];
}
cout<<"nMatrix B:n";
for(i=0;i<r2;i++)
{
cout<<"n";
for(j=0;j<c2;j++)
cout<<B[i][j];
}
cout<<"nProduct Matrix C:n";
for(i=0;i<c1;i++)
{
cout<<"n";
for(j=0;j<r2;j++)
cout<<C[i][j];
}
getch();
}

call by value & call by reference
A function can be invoked in two ways: call by value and call by reference
Call by value
In call by value method the values of actual
parameters (the parameters that appear in a
function call statement i.e. the original values)
are copied into the formal parameters (i.e.
the parameters that appear in function
definition). Here the called function creates its
own copy of argument values for the original

Call by reference
In call by reference a reference to the original
variable is passed. A reference is an alias (i.e.
a different name) for a predefined variable.
This means the original values are referred
here. Here the called function does not creates
its own copy of original values, rather, it refers
to the original values only by different names


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values and uses them i.e. it works with the
duplicate data(s).

i.e. the references i.e. it works with the original
data(s).

In this method if there is any change(s)
occurred in the parameter(s), are not reflected
back to the original values.

In this method if any change(s) occurred in the
parameter(s), are reflected back to the original
values.

Example of call by value method:#include<iostream.h>
#include<conio.h>
void main()
{
clrscr();
void change(int); //prototype declaration
int n;
cout<<"n Enter any number:";
cin>>n;
cout<<"noriginal value="<<n<<endl;
change(n); // function call
cout<<"nValue after function call="<<n<<endl;
getch();
}
//function definition
void change(int n1)
{
n1 = n1 + 5; //number is incremented by 5
cout<<"nValue in function definition="<<n1;
}
Output:
Enter any number:5
original value=5
Value in function definition=10
Value after function call=5 // Here the changes are not reflected
Example of call by reference method:#include<iostream.h>
#include<conio.h>
void main()
{
clrscr();
void change(int &); //prototype declaration (see the syntax)
int n;
cout<<"n Enter any number:";
cin>>n;
cout<<"noriginal value="<<n<<endl;
change(n); // function call
cout<<"nValue after function call="<<n<<endl;
getch();
}
//function definition
void change(int &n1)
{
n1 = n1 + 5; //number is incremented by 5
cout<<"nValue in function definition="<<n1;


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}

Output:
Enter any number:5
original value=5
Value in function definition=10
Value after function call=10
//Here the changes are reflected
Note:

The parameters are also known as arguments.

Reference Variables:- Reference variables are the variables which refer to other variables by a
different name. If we want to create another name of any variable then we have to use reference
variables;
For ex:int a =10;
0x8fc9fff4
int &b = a;
10
Both refer to the same memory area
Where 10 is stored.

a

b

Passing arrays to functions (numeric & string)
Numeric array and string array can be passed as an argument to functions. Whenever we want to
pass a numeric array as an argument to functions we have to provide the array name (Since it
is pointer to its base address i.e. holds the starting address of the array) along with its size.
But in case of character array (i.e. for strings) we need to provide only the array name. This
is because the string is terminated by null character in C++ so the size of the string is
automatically understandable by the compiler.
Let us take examples to illustrate this:
Q To display the highest & lowest marks of 10 students in a particular subject using
array as an argument to a function
#include<conio.h>
void main()
{
void ArrHL(int [ ],int); // prototype declaration
int A[10],i;
cout<<"nEnter the subject marks:n";
for(i=0;i<10;i++)
{
cout<<"marks "<<i+1<<":";
cin>>A[i];
}
ArrHL(A,i); //function call
getch();
}
void ArrHL(int A1[],int n) //arguments are int array A and its size
{
// [ ] indicates it can any size
int H,L;
for(int i=0;i<n;i++)


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{
L=A1[0];
H=A1[0];
if(A1[i]>H)
H=A1[i];
if(A1[i]<L)
L=A1[i];
}
cout<<"nHighest Number="<<H<<endl;
cout<<"nLowest Number="<<L;
}
output
Enter the subject marks:
marks 1:2
marks 2:6
marks 3:8
marks 4:121
marks 5:17
marks 6:19
marks 7:0
marks 8:23
marks 9:25
marks 10:29
Highest Number=29
Lowest Number=2
Q. To find the reverse of a string and its length by passing a character array in a
function.
#include<conio.h>
#include<stdio.h>
void main()
{
clrscr();
int strlencount(char []); // prototype declaration
char str[31];
cout<<"nEnter the string:";
gets(str);
cout<<"nString Length= "<<strlencount(str); //function call
getch();
}
int strlencount(char str1[]) //argument is char array
{
int len=0,i;
for(i=0; str1[i]!='0'; i++)
len++;
for(i=len-1;i>=0;i--)
cout<<str1[i];
//We can also write cout<<str;
return len;
}
Note: - Similarly 2-D array can also be passed as an argument to an array.

Library Functions


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Library is a collection of subprograms used to develop other programs and software.
The C++ library of functions stores functions of same category e.g. mathematical
functions, string functions, character functions etc. under separate files known as
header files.
Header files provide function prototypes, definitions for library functions.
Mathematical functions Header File (math.h)
SL.
NO.
1

Function

2

pow

double pow(double
arg1, double arg2)

3

sqrt

double sqrt (double
num)

4

fabs

double fabs (double
num)

5

log 10

double log10(double
num)

6

log

double log(double
num)

7

fmod

double fmod(double x,
double y)

exp

Prototype (General
Form)
double
exp(double
arg)

Description

Example

The exp( ) function returns the
natural logarithm e raised to the
arg power.
The pow( ) function returns arg1
raised to arg2 power i.e. arg1 arg2
. A domain error occur if arg1
= 0 and arg2 <= 0. Also if
arg1 < 0 and arg2 is not an
integer.
The sqrt( ) function returns the
square root of num. if num < 0
domain error occurs.
The fabs ( ) function returns the
absolute value of num.

exp(2.0)
gives
the value e2.

The log10( ) function returns the
base 10 logarithm for num. A
domain error occurs if num is
negative and a range error is
occurs if the argument num is
zero.
The log( ) function returns the
natural logarithm for num. A
domain error occurs if num is
negative and a range error is
occurs if the argument num is
zero.
The fmod( ) function returns
reamainder of the division x/y.

pow(3,2)
gives
9.
pow(3.0,0) gives
1.
pow(4.0,2.0)
gives 16.
sqrt(9) gives 3
sqrt(81.0) gives
9.0
fabs(2.0)
gives
2.0.
fabs(-3) gives 3.
log 10(1.0) gives
base
10
logarithm for 1.0

log (1.0) gives
natural logarithm
for 1.0

fmod(10.0,4.0)
returns 2.0

Note:- abs ( ) function is used to find the absolute value for integer numbers and mod(
) function is used to find the remainder when one integer is divided by another integer
number.

String functions

Header file string.h

SL.
NO.
1

Function

Description

Example

strcpy(s1,s2)

strcpy(“Vidyalaya”,
“Kendriya”) will give Kendriya.

2

strcat(s1,s2)

This function copies character
string s2 to string s1. The s1
must have enough reserved
elements to hold the string
s2.
This function concatenates
(merges) two strings. The
string s2 will be added at the
end of string s1. The array s1

strcat(“Computer”,”Science”)
will give ComputerScience.


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3

strcmp(s1,s2)

must have enough reserved
elements to hold the string
s2.
This function compares the
strings s1 with s2 on an
alphabetic
element
by
element basis.If s1>s2 then
it return 1 if s1=s2 it return 0
And if s1<s2 it return -1

Strcmp(“KVS”,”KBS”);
It will return -1

Character functions
Header File - ctype.h
Function
int isalnum(int,c)

int isalpha(int,c)

int isalnum(int,c)

int islower(int,c)

int isupper(c)

int toupper(int,c)

int tolower(int,c)

Description
This functions returns nonzero value if its
Argument c is a letter or digit, if the
character is not an alphanumeric then it
returns zero.
Argument c is a alphabet if the character is
not an alphanumeric then it returns zero.
Argument c is a digit, if the c is not digit
then it returns zero.
Argument c is in lowercase letter, otherwise
it returns zero.
Argument c is in uppercase letter, otherwise
it returns zero.
This functions returns uppercase equivalent
of c if c is already in upper case it remains
unchange.
This functions returns lowercase equivalent
of c if c is already in lower case case it
remains unchanged.

Example
char c=’A’
if (isalnum( c))
cout<<”Alphanum”;
if (isalpha( c))
cout<<”Alphabet”;
if (isdigit( c))
cout<<”Digit”;
if (islower( c))
cout<<”Lower
case”;
if (isupper( c))
cout<<”Upper
case”;
Char c=’a’
cout<<toupper(c);
output A
Char c=’A’
cout<<tolower(c);
output a

Questions
Array
1.Write a program in C++ to interchange the values of the row and column.
2 Write a user define function xyz() which takes a two dimensional array with size N rows and N
columnsas argument and store all 1)even in one dimensional array2) All odd in one dimensional
array 3. display product of all the number except those which are not divisible by either 5 or 3.
4. write a user define function unitdigit() which takes a two dimensional array with size N rows
and M columns as argument and store all i) unit digit ii) except unit digit
In two dimensional array. i.e
A[2][3] = 200
213
56
657
Resultant array should be
i)
A[2][3] =
0
3
6
7
ii)
A[2][3] =
20
21
5
65
5. Write a user define function repeat() which takes a two dimensional array with size N rows
and M columns as argument and convert all repeated element into zero.


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6. Write a user define function convert() which takes a one dimensional array with size N as
argument and convert it into two dimensional array.
Suppose arr[6]= { 1,2,3,4,5,6}
Resultant array should be
Arr[6][6] = 2
1 4 36 5
2 1 4 36 0
2 1 4 30 0
2 1 4 00 0
2 1 000 0
2 0 0 00 0
Write a function in C++ to replace the repeating elements in an
array by 0 . The zeros should be shifted to the end. Do not use
parallel array . The order of the array should not change.
(2)



Eg : Array

: 10 , 20 , 30 , 10 , 40 , 20 , 30

Result : 10 , 20 , 30 , 40 , 0 , 0 , 0
7. Write a function in C++ called shift( ) to rearrange the matrix as shown . Do not use parallel
matrix .
(2)
Original Matrix
1
0
-3

2
-1
9

-3
2
-4

Rearranged Matrix
-2
1
4

-3
-1
-3

-2
0
-4

1
2
9

2
1
4

8. Find the output of the following program:
#include <iostream.h>
void modify(int arr[ ], int N)
{
for (int I=1;I<N;I++)
arr[ I-1]+=arr[ I ];
}
void main()
{
int P[]={1,2,3,4},Q[]={5,10,15,20,30};
modify(P,4);
modify(Q,5);
for (int L=0;L<4;L++)
cout<<P[L]<<”$”;
cout<<endl;
for (L=0;L<5;L++)
cout<<Q[L] <<”$”;
cout<<endl;
}

9. Find the output of the following program:
#include <iostream.h>
int a=5;


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void sample( int &x, int y , int *z)
{
a+=x;
y*=a;
*z=a+y;
cout<<a<<” “ <<x<<” “<< y<<” “<<*z<<”n”;
}
void main()
{
clrscr();
int a =7 ,int b = 5 ;
sample(::a , a , &b);
cout<< ::a << “ “ << a <<” “<<b <<”n”;
sample(::a , a , &b);
cout<< ::a << “ “ << a <<” “<<b <<”n”;
}
10. Write a function in C++ to add new objects at the bottom of a binary file “TICKET.DAT”,
assuming the binary file is containing the objects of the following class.

class LOTTERY
{
int LotTicNo;
char StateCode[5];
public:
void Enter(){cin>>LotTicNo;gets(StateCode);}
void Display(){cout<<LotTicNo<<StateCode<<endl;}
};

11.

Write a function in C++ that will read the contents of a file
EXAM.DAT and display the details of those students whose marks>75.
The binary file EXAM.DAT containing records of student.
2
class student
{
char roll [4];
char name[20];
int marks;
public :
void Read_Data ( ) ;
// Entering data in to the file
void Show_Date ( );
//Displaying the content of the file

12 . Find the output of the following program. Assume that all required headers files have been
included.

2
int funs (int &x, int y=10)
{
if (x%y == 10)
return ++x;
else
return y-- ;
}
void main( )
{
int p=20, q=23;
q = funs(p,q);
cout <<p<<”;”<<q<< endl;
q = funs(p);


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cout <<p<<”;”<<q<<endl;
}


Arrays and library functions

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