Computer Programming- Lecture 10

Lecture 10
Arrays,
Functions &
Structures

TCP1231 Computer Programming I 1

Objectives

• To Learn about functions and arrays
• Explore how to declare and manipulate arrays
with functions
• Explore how to declare and manipulate structures
with functions
• Become familiar with functions, arrays, and
structures.


Functions – Revisited
(User Defined Function)
• Two components of a function definition
• Function declaration (or function prototype)
– Shows how the function is called
– Must appear in the code before the function can be
called
– Syntax:
Type_returned Function_Name(Parameter_List);
//Comment describing what function does


Functions – Revisited
(User Defined Function)
• Function definition
– Describes how the function does its task
– Can appear before or after the function is called
– Syntax:
Type_returned Function_Name(Parameter_List)
{
//code to make the function work
}


#include <iostream>
using namespace std; int p(int x, int n) {
int temp=1;
int p(int x, int n); Function for (int i=1; i <= n; i++) Function
int f(int x); declaration
temp= temp * x; definition
return temp;
int main() { }
int no, x, n;
cout << "Enter a number==> "; int f(int x) {
cin >> no; int temp=1;
cout << "factorial = "<<f(no); for (int i=1; i <= x; i++)
cout << "nnEnter number 1==> "; temp= temp * i;
cin >> x; return temp;
cout << "Enter number 2==> "; }
cin >> n;
cout << "power = "<<p(x,n);

system(“PAUSE”);
return 0; Function call
}


Structure and Function Calls

• Structure definition is generally placed outside
any function definition
– This makes the structure type available to all code
that follows the structure definition

• To declare two variables of type CDAccount:

CDAccount my_account, your_account;

– My_account and your_account contain distinct
member variables balance, interest_rate, and term


Structures as Arguments

• Structures can be arguments in function calls
– The formal parameter can be call-by-value
– The formal parameter can be call-by-reference

• Example:
void get_data(CDAccount& the_account);

– Uses the structure type CDAccount as the type
for a call-by-reference parameter


A Structure Definition
//Program to demonstrate the CDAccount structure type.
#include <iostream>
using namespace std;
//Structure for a bank certificate of deposit:
struct CDAccount
{
double balance;
double interest_rate;
int term; //months until maturity
}; Function declaration:
To receive struct
CDAccount as
void get_data(CDAccount& the_account); argument

//Postcondition: the_account.balance and the_account.interest_rate
//have been given values that the user entered at the keyboard.


int main( )
{
CDAccount account;
Function calling :
get_data(account); Send account as
get_data argument

double rate_fraction, interest;
rate_fraction = account.interest_rate / 100.0;
interest = account.balance * rate_fraction * (account.term / 12.0);
account.balance = account.balance + interest;

cout.setf(ios::fixed);
cout.setf(ios::showpoint);
cout.precision(2);
cout << "When your CD matures in " << account.term << " months,n"
<< "it will have a balance of $" << account.balance << endl;
return 0;
}


void get_data(CDAccount& the_account)
{
cout << "Enter account balance: $";
cin >> the_account.balance;
cout << "Enter account interest rate: "; Function definition :
Manipulating
cin >> the_account.interest_rate; the_account inside
cout << "Enter the number of months until get_data
implementation
maturityn“
<< "(must be 12 or fewer months): ";
cin >> the_account.term;
}
Enter account balance: $100.00
Sample Output:
Enter account interest rate: 10.0
Output:
Enter the number of months until maturity(must
be 12 or fewer months): 6
When your CD matures in 6 months, it will have
a balance of $105.00


Structures as Return Types
• Structures can be the type of a value returned by
a function
students reading(){
• Example: students rec;
cout << "nEnter the student name ==> ";
getline(cin, rec.name);
cout << "Enter the student ID ==> ";
cin >> rec.id;
cout << "Enter the student Mark ==> ";
cin >> rec.mark;
cin.ignore();
return rec;
}


#include <iostream> To read info about three students
using namespace std; void printing(students rec)
{
struct students{ cout << "nThe student name: ";
string name; cout << rec.name;
int id; cout << "nThe student ID: ";
double mark; cout << rec.id;
}; cout << "nThe student mark: ";
students reading() cout << rec.mark;
{ }
students rec; int main() {
cout << "nEnter the student name ==> "; int i;
getline(cin, rec.name); students info[3];
cout << "Enter the student ID ==> "; for (i=0; i<=2; i++)
cin >> rec.id; info[i]=reading() ;
cout << "Enter the student Mark ==> ";
cin >> rec.mark; for (i=0; i<=2; i++)
cin.ignore(); printing(info[i]);
return rec;
} return 0;
TCP1231 Computer Programming I } 12

Arrays in Function

• Indexed variables can be arguments to functions
– Example: If a program contains these declarations:
int i, n, a[10];
void my_function(int n);

Variables a[0] through a[9] are of type int, making
these calls legal:
my_function( a[ 0 ] );
my_function( a[ 3 ] );
my_function( a[ i ] );


Array as Function Arguments

• A formal parameter can be for an entire array
– Such a parameter is called an array parameter
• It is not a call-by-value parameter
• It is not a call-by-reference parameter

• Array parameters behave much like call-by-
reference parameters


Array Parameter Declaration

• An array parameter is indicated using empty
brackets in the parameter list such as

void fill_up(int a[ ], int size);


Function with an Array Parameter

#include<iostream>
Function declaration:
To receive an array of
void fill_up(int a[], int size); int, a[] as
//Precondition: size is the declared size of the array a. argument
// The user will type in size integers.
//Postcondition: The array a is filled with size integers
// from the keyboard.

void fill_up(int a[], int size)
{
cout << "Enter " << size << " numbers:n";
for (int i = 0; i < size; i++) Function definition :
Manipulating a[]
cin >> a[i]; inside fill_up
size--; implementation
cout << "The last array index used is " << size << endl;
}


Function calls with array

• If function fill_up is declared in this way:

and array score is declared this way:
int score[5], number_of_scores;

fill_up is called in this way:
fill_up(score, number_of_scores);


Function call details

• A formal parameter is identified as an array
parameter by the [ ]'s with no index expression


• An array argument does not use the [ ]'s

fill_up(score, number_of_scores);


Array Formal Parameters

• An array formal parameter is a placeholder for
the argument

– When an array is an argument in a function call,

an action performed on the array parameter is
performed on the array argument

– The values of the indexed variables can be
changed by the function


Array Parameter Considerations

• Because a function does not know the size of
an array argument…
– The programmer should include a formal parameter
that specifies the size of the array
– The function can process arrays of various sizes
• Function fill_up can be used to fill an array of any
size:

fill_up(score, 5);
fill_up(time, 10);


Returning An Array

• Recall that functions can return a value of
type int, double, char, …, or a class type

• Functions cannot return arrays

• We learn later how to return a pointer to an array


#include <iostream> To read 9 numbers
void ReadArray(int arr[] ) {
int i; int main() {
for (i=0; i < 9; i++) int i;
{ cout << "a["<<i<<"]="; int a[9];
cin >> arr[i];
} ReadArray(a);
}
for (i=0; i < 9; i++)
cout << a[i] << 't';

system(“pause”);
return 0;
}


#include <iostream> To read 9 numbers, then sort
using namespace std; them in ascending order
void ReadArray(int arr[] ) { int main() {
int i; int i;
for (i=0; i < 9; i++) int a[9];
{ cout << "a["<<i<<"]=";
cin >> arr[i]; ReadArray(a);
}
} for (i=0; i < 9; i++)
// Bubble sort cout << a[i] << 't';
void sorting(int arr[] ) { cout << endl;
int i, j, temp;
for (i=0; i < 9; i++) sorting(a);
for (j=0; j < 8; j++)
if (arr[j] > arr[j+1]) for (i=0; i < 9; i++)
{ temp= arr[j]; cout << a[i] << 't';
arr[j]= arr[j+1];
arr[j+1]= temp; system(“pause”);
} return 0;
} }

Functions and
Multidimensional Array
• When a one-dimensional array is defined as
a formal parameter, the size of the array
may be omitted

void Fun(float list[], int size) {
. . .
}


Multi Dimensional Array as Parameter

• With two-dimensional arrays, the first dimension (number of
rows) may be omitted, but not the second dimension (number of
columns).
void Fun(float table[ ][5], int rows, int
cols){
. . .
}
• You can specify both dimensions if you choose to.
void Fun(float table[2][5], int rows, int
cols){
. . .
}


#include <iostream>
const int row=3; To two dimensional array
const int col=4; then display its elements
void Read2Array(int arr[][col] ) {
int i,j;
for (i=0; i<row; i++)
for ( j=0; j<col; j++)
cin >> arr[i][j]; int main ()
} {
int a[row][col];
void writing(int arr[][col]) {
int i,j; Read2Array(a);
for (i=0; i<row; i++) writing(a);
{
for ( j=0; j<col; j++) system(“pause”);
cout << arr[i][j] << 't'; return 0;
cout << endl; }
}
}

#include <iostream> To multiply two arrays
void multi(int a[][3], int b[][4], int c[][4]) { int main ()
{
int i, j, k; int x[3][3]= {{12, 4, 9}, { -5, 3,
for (i=0; i<3; i++) 1}, { 9, 2, -2}};
for ( j=0; j<4; j++)
{ int y[3][4]= {{11, 1, 12, 1},{ 2,
c[i][j]=0; 24, 32, 4}, {63, -3, 3, 4}} ;
for ( k=0; k<3; k++)
c[i][j]= c[i][j] + a[i][k] * b[k][j]; int z[3][4];
}
} multi(x, y, z);
void writing(int arr[][4]) { writing(z);
for (int i=0; i<3; i++)
{ system(“pause”);
for ( int j=0; j<4; j++) return 0;
cout << arr[i][j] << 't'; }
cout << endl;
}
} TCP1231 Computer Programming I 27

The End


Computer Programming- Lecture 10

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