Computer Programming- Lecture 9

Lecture 9
Arrays and
Functions

TCP1231 Computer Programming I 1

Objectives

• To Learn about arrays
• Explore how to declare and manipulate data
into arrays
• Understand the meaning of “array index out of
bounds”
• Become familiar with the restrictions on array
processing


Two kinds of Multidimensional
Arrays
There are two basic ways of implementing 2-
dimensional arrays:
 true two-dimensional arrays, and
 arrays of arrays.

Some languages use one method, some another,
and some both.

C++ allows both methods, and each has its
advantages and disadvantages.

Two kinds of Multidimensional
Arrays
1. True arrays
• In this case the rows are laid out sequentially in memory.
• This provides simplicity in memory management and a slight
speed advantage.
• This is the kind of array C/C++ creates by default.

1. Arrays of arrays
• In this style each element of a one-dimensional array is a
pointer to another array.
• It's a common way to create an array of C-strings.
• The disadvantage is that memory management can be a little
more complex and there is a slight performance overhead.


Multidimensional Array Declaration

Syntax

Type Array_Name[Size_Dim_1][Size_Dim_2] . . . [Size_Dim_Last];

Examples

char page[30][100];
int matrix[2][3];
double three_d_picture[10][20][30];

An array declaration, of the form shown, defines one indexed variable for each
combination of array indexes. For instance, the second of the sample declarations
defines the following six indexed variables for the array matrix:

matrix[0][0], matrix[0][1], matrix[0][2],
matrix[1][0], matrix[1][1], matrix[0][2]


Multidimensional Array Parameters
When a multidimensional array parameter is given in a function
heading or function declaration, the size of the first dimension
is not given, but the remaining dimension sizes must be given in
square brackets.
Since the first dimension size is not given, we usually need an
additional parameter of type int that gives the size of this first
dimension.
Below is an example of a function declaration with a two-
dimensional array parameter p:

void get_page(char p[][100], int size_dimension_1);


#include <iostream>
using namespace std;

int main ()
{
int col, row;

for (row=0; row <=2; row++)
a[0,0] a[0,1] a[0,2]
{
for (col=0; col <=2; col++) a[1,0] a[1,1] a[1,2]
cout << "a[" <<row << "," << col << "] "; a[2,0] a[2,1] a[2,2]
cout << endl;
}

system(“pause”);
return 0;
}


#include <iostream>
using namespace std; Read an array of 3x3
then print its elements
int main ()
{ input a[0,0]= 5
int col, row; a[0,1]= -6
int a[3][3]; a[0,2]= 1
a[1,0]= 7
for (col=0; col <=2; col++)
{ a[1,1]= 88
cout << "a[" <<row << "," << col << "]= "; a[1,2]= 2
cin >> a[row][col]; a[2,0]= 0
} a[2,1]= 5
a[2,2]= 9
{
cout << a[row][col] << 't'; output 5 -6 1
cout << endl; 7 88 2
} 0 5 9
}

#include <iostream>
using namespace std; Read an array of 3x3
then print Max. No.
int main ()
{ input
int col, row, max; a[0,0]= 5
int a[3][3]; a[0,1]= -6
for (row=0; row <=2; row++) a[0,2]= 1
a[1,0]= 7
{
cout << "a[" <<row << "," << col << "]= "; a[1,1]= 88
cin >> a[row][col]; a[1,2]= 2
} a[2,0]= 0
max=a[0][0]; a[2,1]= 5
a[2,2]= 9
if (max< a[row][col]) output
max=a[row][col]; Max= 88
cout << "nMax= " << max;
}

#include <iostream>
using namespace std; Convert Tow-Dimensional Array a(3x3)
to One Dimensional Array b(9)
int main ()
{ input
int col, row, i, j, c=0; a[0,0]= -5
int a[3][3], b[9]; a[0,1]= 4
for (row=0; row <=2; row++) a[0,2]= 97
a[1,0]= -6
{
cout << "a[" <<row << "," << col << "]= "; a[1,1]= 5
cin >> a[row][col]; a[1,2]= -8
} a[2,0]= -1
for (int i=0; i<3; i++) a[2,1]= 44
for (int j=0; j<3; j++)
a[2,2]= 2
{ b[c]=a[i][j]; c++; }
output
for (int i=0 ;i<9; i++)
cout << b[i] << 't'; -5 4 97 -6 5 -8 -1 44 2
}

#include <iostream>
using namespace std; C(4x3) equal A (4x3) + B (4x3)
int main () {
int a[4][3]= {{12, 4, 9}, { -5, 3, 1}, { 9, 2, -2}, {3, 2, 22}};
int b[4][3]= {{11, 1, 12},{ 2, 24, 32}, {63, -3, 3}, {4, -4, 4}} ;
int i, j, c[4][3];

for (i=0; i<4; i++)
for ( j=0; j<3; j++)
c[i][j]= a[i][j] + b[i][j];
for (i=0; i<4; i++)
{
for ( j=0; j<3; j++)
cout << c[i][j] << 't'; 23 5 21
cout << endl; -3 27 33
} 72 -1 1
system(“pause”); 7 -2 26
return 0;
}

#include <iostream>
using namespace std; C(4x3) equal A (4x3) + B (4x3)
int main () {
int a[4][3]= {{12, 4, 9}, { -5, 3, 1}, { 9, 2, -2}, {3, 2, 22}};
int b[4][3]= {{11, 1, 12},{ 2, 24, 32}, {63, -3, 3}, {4, -4, 4}} ;
int i, j, c[4][3];
cout << "n***** B ******n"; **** A *****
for (i=0; i<4; i++) 12 4 9
for (i=0; i<4; i++) -5 3 1
for ( j=0; j<3; j++) { 9 2 -2
c[i][j]= a[i][j] + b[i][j]; for ( j=0; j<3; j++) 3 2 22
cout << b[i][j] << 't';
***** B *****
cout << "n***** A ******n"; cout << endl; 11 1 12
for (i=0; i<4; i++) } 2 24 32
{ cout << "n******C ******n"; 63 -3 3
for ( j=0; j<3; j++) 4 -4 4
for (i=0; i<4; i++)
cout << a[i][j] << 't'; { ***** C *****
cout << endl; for ( j=0; j<3; j++) 23 5 21
} cout << c[i][j] << 't'; -3 27 33
72 -1 1
cout << endl; 7 -2 26
}
}

Functions
What is a function?
• A program can be thought of as consisting
subparts, such as obtaining the input data,
calculating the output data and displaying the
output data.

• C++, like most programming languages, has
facilities to name and code each of these subparts
separately.

• In C++ these subparts are called functions.


Predefined Functions


//Computes the size of a dog house that can be purchased given the
//user’s budget
#include <iostream>
#include <cmath>
int main()
{
const double COST_PER_SQ_FT = 10.50;
double budget, are, length_side;
cout << "Enter rhe amount budgeted for your dog house $";
cin >> budget;
area = budget/COST_PER_SQ_FT;
length_side = sqrt(area);
cout.setf(ios::fixed);
cout.setf(ios::showpoint);
cout.precision(2);
cout << "For a price of $" << budget << endl
<< "I can build for you a luxurious square dog housen"
<< "that is " << length_side
<< "feet on each side.n";
Enter the amount budgeted for your dog house: $ 25.00
return 0; For a price of $ 25.00
I can build you a luxurious square dog house
} TCP1231 Computer Programming I feet on each side. 15
that is 1.54

Programmer-Defined Functions
• We can define our own functions, either in the
same file as the main part of our program of in a
separate file so that the functions can be used by
several different programs.


Functions
There are two components to define a function:

1. Function declaration (or function prototype)
* Shows how the function is called
* Must appear in the code before the function can be called
* Normally placed before the main part of your program

2. Function definition (or function body)
* Describes how the function does its task
* Can appear before or after the function is called
* Normally placed after the main part of your program or in
a separate file.


Function Declaration
• Syntax:
data_type Function_Name(Parameter_List);

parameter list

data type function name parameters type formal parameters name

double total(int number, double price);
// Compute total cost including 5% sales tax on ;
// number_par items at cost of price_par each


Function Definition
• Syntax:
data_type Function_Name(Parameter_List);

function header

double total(int number, double price)
{
double tax= 0.05; function
double subtotal; body
subtotal= number * price_par - tax;
return subtotal;
}

return statement

#include <iostream>
using namespace std; function declaration
double total_cost(int number_par, double price_par);
//Computes the total cost, including 5% sales tax, on number_par
//items at a cost of price_par each.
int main()
{
double price, bill;
int number;
cout << "Enter the number of items purchased: ";
cin >> number; function call
cout << "Enter the price per item $";
cin >> price;
bill = total_cost(number, price); Enter the number of items purchased: 2
Enter the price per item: $10.10
cout.setf(ios::fixed); 2 items at $10.10 each.
cout.setf(ios::showpoint);
cout.precision(2); Final bill, including tax, is $21.21
cout << number << " items at "
<< "$" << price << " each.n”
<< "Final bill, including tax, is $" << bill
<< endl;
return 0; function heading
}
double total_cost(int number_par, double price_par)
{
const double TAX_RATE = 0.05; //5% sales tax function
double subtotal; function body definition
subtotal = price_par * number_par;
TCP1231 Computer Programming I
return (subtotal + subtotal*TAX_RATE); 20

The Return Statement

• A return statement consists of the keyword return followed by
an expression.

• When a return statement is executed, the function call ends

• Returns the value calculated by the function

• A void function is does not necessarily contain a return
statement, however it may optionally have one or more return
statement.


The Return Statement

• Syntax
return expression;
• expression performs the calculation
or
• expression is a variable containing the calculated
value

• Example
return (subtotal + subtotal * tax);
or
return subtotal + subtotal * tax;


Function Call
• A function call is an expression consisting of the
function name followed by arguments enclosed in
parentheses.

• If there is more than one argument, the arguments
are separated by commas.

• A function call is an expression that can be used
like any other expression of the type specified for
the value returned by the function.


The Function Call
Syntax

Function_Name(Argument_List);

where the Argument_list is a comma-separated list of arguments:

Argument_1, Argument_2, . . ., Argument_Last

Examples

arguments list
function name

bill = total(number, price);

return value assigned to bill

Void-Function

What is a void-function?

• Subtasks are implemented as functions in C++.

• In C++, a function must either return a single
value or return no values at all.

• A function that returns no value is called a void
function.


Void-Function
void Function_Name(Parameter_List);

There are two main differences between void-function
definitions and the definitions of functions that return one value:

1. Keyword void replaces the data type of the function
2. No return statement


Syntax for a void Function Declaration

void Function Declaration arguments list
function name
void Function_Name(Parameter_List);
Function_Declaration_Comment print (average, min, max);
void Function Definition

void Function_Name(Parameter_List) function header
{
Declaration_1
Declaration_2 void print (int number, double price)
body ...
{
Declaration_Last
Executable_Statement_1
double tax= 0.05;
Executable_Statement_2 double subtotal;
...
Executable_Statement_Last subtotal= number * price_par -
} tax;
cout << subtotal;
}

#include <iostream>
Multiply a number by itself
int sqr(int x) // to duplicate a number
{
int y;
y= x*x;
return y;
}
int main ()
{
int a, b;
a=3; 3 9
b=sqr(a);
cout << a << 't' <<b;

system(“pause”);
return 0;
}

#include <iostream>

double XtothepowerN(int x, int n) x to the power of n
// to find X to the power of n
{
double p=1;
for (int i=1; i<= n; i++)
p=p * x;
return p;
}
int main ()
{
int b; the result is 81
b=XtothepowerN(3,4);
cout << "the result is " << b;
return 0;
}


A function is like a small program
• To understand functions, keep the following three points in mind:

– A function definition is like a small program and calling the
function is the same thing as running this “small program”.

– A function uses formal parameters, rather than cin, for input. The
arguments to the function are the input and they are plugged in for
the formal parameters.

– A function does not normally send any output to the screen, but it
does send a kind of “output” back to the program. The function
returns a value, which is like the “output” for the function. The
function uses a return statement instead of a cout statement for
this “output”.


THE END


Computer Programming- Lecture 9

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