computer programming- lecture 10

1TCP1231 Computer Programming I

Lecture 10Arrays,

Functions & Structures


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 f(int x);

int main() { int no, x, n; cout << "Enter a number==> "; cin >> no; cout << "factorial = "<<f(no); cout << "\n\nEnter number 1==> "; cin >> x; cout << "Enter number 2==> "; cin >> n; cout << "power = "<<p(x,n); system(“PAUSE”); return 0;}

Function declaration

int p(int x, int n) { int temp=1; for (int i=1; i <= n; i++) temp= temp * x; return temp;}

int f(int x) { int temp=1; for (int i=1; i <= x; i++) temp= temp * i; return temp; }

Function definition

Function call


Structure and Function Calls

• Structure definition is generally placed outsideany 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


//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};

void get_data(CDAccount& the_account);//Postcondition: the_account.balance and the_account.interest_rate//have been given values that the user entered at the keyboard.

A Structure Definition

Function declaration:To receive struct CDAccount as argument


int main( ){ CDAccount account; get_data(account);

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;}

Function calling :Send account as get_data argument


void get_data(CDAccount& the_account){ cout << "Enter account balance: $"; cin >> the_account.balance; cout << "Enter account interest rate: "; cin >> the_account.interest_rate; cout << "Enter the number of months until

maturity\n“ << "(must be 12 or fewer months): "; cin >> the_account.term;}

Function definition :Manipulating the_account inside get_data implementation

Enter account balance: $100.00

Enter account interest rate: 10.0

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

Output:

Sample Output:


Structures as Return Types

• Structures can be the type of a value returned bya function

• Example:students reading(){

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;}



struct students{ string name; int id; double mark;};students reading(){ 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;}

void printing(students rec){ cout << "\nThe student name: "; cout << rec.name; cout << "\nThe student ID: "; cout << rec.id; cout << "\nThe student mark: "; cout << rec.mark;}int main() { int i; students info[3]; for (i=0; i<=2; i++) info[i]=reading() ; for (i=0; i<=2; i++) printing(info[i]); return 0;}

To read info about three students


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 emptybrackets in the parameter list such as

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


Function with an Array Parameter

#include<iostream>using namespace std;

void fill_up(int a[], int size);//Precondition: size is the declared size of the array a.// 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++) cin >> a[i]; size--; cout << "The last array index used is " << size << endl;}

Function declaration:To receive an array of int, a[] as argument

Function definition :Manipulating a[] inside fill_up implementation


Function calls with array

• If function fill_up is declared in this way: void fill_up(int a[ ], int

size);

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

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

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

fill_up(score, number_of_scores);


Array Formal Parameters

• An array formal parameter is a placeholder forthe 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



void ReadArray(int arr[] ) { int i; for (i=0; i < 9; i++) { cout << "a["<<i<<"]="; cin >> arr[i]; }}

int main() { int i; int a[9]; ReadArray(a); for (i=0; i < 9; i++) cout << a[i] << '\t'; system(“pause”); return 0;}

To read 9 numbers



void ReadArray(int arr[] ) { int i; for (i=0; i < 9; i++) { cout << "a["<<i<<"]="; cin >> arr[i]; }}// Bubble sortvoid sorting(int arr[] ) { int i, j, temp; for (i=0; i < 9; i++) for (j=0; j < 8; j++) if (arr[j] > arr[j+1]) { temp= arr[j]; arr[j]= arr[j+1]; arr[j+1]= temp; }}

int main() { int i; int a[9]; ReadArray(a);

for (i=0; i < 9; i++) cout << a[i] << '\t'; cout << endl; sorting(a);

for (i=0; i < 9; i++) cout << a[i] << '\t';

system(“pause”); return 0;}

To read 9 numbers, then sort them in ascending order


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){ . . . }



const int row=3;const int col=4;

void Read2Array(int arr[][col] ) { int i,j; for (i=0; i<row; i++) for ( j=0; j<col; j++) cin >> arr[i][j];}

void writing(int arr[][col]) { int i,j; for (i=0; i<row; i++) { for ( j=0; j<col; j++) cout << arr[i][j] << '\t'; cout << endl; } }

int main () { int a[row][col]; Read2Array(a); writing(a); system(“pause”); return 0;}

To two dimensional array then display its elements



void multi(int a[][3], int b[][4], int c[][4]) { int i, j, k; for (i=0; i<3; i++) for ( j=0; j<4; j++) { c[i][j]=0; for ( k=0; k<3; k++) c[i][j]= c[i][j] + a[i][k] * b[k][j]; }}void writing(int arr[][4]) { for (int i=0; i<3; i++) { for ( int j=0; j<4; j++) cout << arr[i][j] << '\t'; cout << endl; } }

int main () { int x[3][3]= {{12, 4, 9}, { -5, 3, 1}, { 9, 2, -2}};

int y[3][4]= {{11, 1, 12, 1},{ 2, 24, 32, 4}, {63, -3, 3, 4}} ;

int z[3][4];

multi(x, y, z); writing(z); system(“pause”); return 0;}

To multiply two arrays


The End

computer programming- lecture 10

Education

function function definition

int n function

function work

function prototype

int temp

functions revisiteduser

structureswith functions

arrayswith functions