ch4 modular programming

7/30/2019 Ch4 Modular Programming

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Modular Programming

Zarina TukiranDept. of Computer Engineering

Faculty of Electrical & Electronic EngineeringEmail: [email protected]

Office No.: 07-4537566

1Sem II Session 2012/2013


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2

Objectives :

understand the concept of modularity in

programming.

introduce the common functions available in the C++standard library.

able to write a user-defined function in C++.

Sem II Session 2012/2013


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Introduction

The C++ program describes in Chapter 1 through

Chapter 3 uses only the function main; the programming

instructions are packed into one function.

This technique, however, is good for a short program.

For large program, it is not practical to put the entire

programming instructions into one function. It must bebroke into manageable pieces (modules / subroutines)

called functions.



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Hierarchical modular design technique

Modularization (divide and conquer)

The complexity of design in broken down (divided) into a

hierarchy of modules/routines; from general (top) tospecific (bottom).

Benefits:

Focus on a single module at a time. Create customised low-level modules for design

reuse.

Avoid the repetition of writing out the same segment

of code. 4Sem II Session 2012/2013


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Hierarchical modular design technique (cont)

Top-down decomposition partitions the system into

smaller subsystems up to a level which the subsystems

can be realised.

Bottom-up composition integrates and connects

available modules to form bigger, more complex

subsystems.



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Categories of Functions

There are two types of functions:

Predefined function

User-defined function



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Pre-defined function

Review a concept from a algebra course.

In algebra, a function can be considered a rule or

correspondence between values, called thefunctions

arguments, and the unique value of the function

associated with the arguments.

Thus, if f(x)=2x+5, then f(1)=7, f(2)=9, and f(3)=11,where 1,2 and 3 are the arguments of f, and 7, 9 and 11

are the corresponding values of the function f.



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Pre-defined function (cont)

In C++, the concept of a function, either predefined or user-

defined, is similar to that of a function in algebra.

For example, every function has a name and depending

on the values specified by the user, it does some

computation. Some of the predefined mathematical

functions arepow(x,y), sqrt(x) andfloor(x).

In C++, predefined functions are organized into separate

libraries. For example, the header file iostream contains I/O

functions and the header file cmath contains math functions.



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Pre-defined function (cont)

Table below lists some of the predefined functions, the name

of the header file in which each functions specification can be

found, the data type of the parameters and the function type.

The function type is the data type of the final value returned

by the function.

Function Header File PurposeParameter(s)

typeResult

ceil (x) Returns the smallest whole number that is

not less than x: ceil (56.34)=57.0double double

cos (x)

Returns the cosine of angle x: cos(0.0)=1.0 double

(radians) double

exp (x) Returns ex, where e=2.718: exp

(1.0)=2.71828double double

tolower(x) Returns the lowercase value of x if x is

uppercase; otherwise, returns xint int

topupper(x) Returns the uppercase value of x if x is

lowercase; otherwise, returns x

int int



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User-defined function

C++ does not provide every function that we will ever need

and designers cannot possibly know a users specific needs,

we need to write our own functions this is called user-

defined functions.

User-defined functions in C++ are classified into two

categories:

value-returning functions functions that have a

return type. These functions return a value of a specific

data type using the return statement.

void functions functions that do not have a return

type. These functions do not use a return statement to

return a value. 11Sem II Session 2012/2013


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Function Elements

There are three function elements:

Function definition

Function call

Function prototype



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Function Elements: Function Definition

General syntax

returnValueType funct ionName(formal parameters list)

{/*function body*/

}



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Function Elements: Function Definition (cont)

Example 1 (value-returning function)

int add(int a, int b)

{

int sum;

sum = a + b;

return sum;

}

add

int a int b

int sum

Function name

Formal parameter list

Return Value Type

Pictorial view of value-

returning function



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Example 2 (value-returning function)

double circ leArea( )

{

doube r, area;

const double PI=3.142;

coutr;

area=PI*(r*r);

return (area);

}

circleArea

double area

Function name

Empty formal parameter list

Return Value TypePictorial view of value-

returning function



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Example 3 (void function)

void decide(char letter, int n)

{

if ((letter == A) && (n==100))

cout


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Example 4 (void function)

void circ leArea( )

{

doube r, area;

const double PI=3.142;

coutr;

area=PI*(r*r);

cout


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Function Elements: Function Call

A function is executed if it is calledorinvoked.

In C++, the function calls can be called by :

The main function

User-definedfunction user-defined function call other user-defined

function

Call itself (recursion method)

There are two ways to call/invoke a function: call-by-value

call-by-reference



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Function Elements: Function Call

General Syntax:

(a) use the following format forvalue-returning function.

variableName = functionName (list of actual parameters);

Example 5: (call-by-value)

y = findMin (a, b);



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Function Elements: Function Call (cont)

(b) use the following format forvoid function

functionName (list of actual parameters);

Example 6: (call-by-value)

view (x);

Example 7: (call-by-reference)

calculate (&num, &x, &y);



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Function Elements: Function Call (cont)

Call-by-value

The value holds by actual parameter is copied to the

formal parameter.

If the variable within the function is modified then uponreturn from the function, the value of actual variable is

not modified.

Call-by-reference The address of actual parameter is copied to the formal

parameter.

If the variable within the function is modified then the

value of actual variable is modified. 21Sem II Session 2012/2013


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Function Elements: Function Prototype

The function prototype

is an important feature.

tells the compiler what type of value the function returns,

number and types of parameters, and order in whichthese parameters are expected.

must added to a C++ program before the main function,

if call the function before defining it.

is not needed in a C++ program if the function is calledafterfunction definition.



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Function Elements: Function Prototype (cont)

General syntax

returnValueType funct ionName(formal parameters list) ;

Example:

bool accept(char let1, char let2) ;

More examples:

void display() ;

void gName(float m) ;

doub letemp(float t1, float t2) ;

float dSeries(float r[]) ;23Sem II Session 2012/2013


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Given the following.Lets say you have the following function definition

and the function calls are as follows.

j=op(a,b);

mul (z);

The function prototypes are as follows:

float op (float a, float b); void mul (int z);

void mul (int z)

{ int m;

m=z*5;

cout


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Thus,

the

fullprogra

m:

#include

using namespace std;

float oper (float a, float b);//function prototype of op

void mul (int z);//function prototype of mul

//===========main function======================

void main(){

floatj;

j=oper (2.4,2.0); //function call to op

cout


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ADDITIONAL: Custom Header File

Programmer can create custom header files

should end in .h

e.g. myfunct ion l ib .h

To insert the custom header file in a C++ program using

pre-processor directive. Example:

#include myfunctionlib.h



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Practice



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Exercise 1: Familiarise the concept

Write C++ statements that provide a function definition, calland prototype for the following description.

1. A user-defined function named myWish which able to

display I want grade A for C++ only once.2. A user-defined function named repeatWish which able

to display I want grade A for C++ 10 times.

3. A user-defined function named minus which able to find

the subtraction of three numbers.4. A user-defined function named FindMaxwhich able to

determine the highest value of two integer numbers.



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Exercise 2: Implementation of concept in the

program

Now, integrate all user-defined function (Exercise 1) in a

single C++ program.



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Exercise 3: More Programming

Write C++ program for each problem statements. Implementmodular programming in your program.

Problem Statement 1: Counti ng posit ive and negative numbers and computi ng the

average of numbers.

Write a program that reads an unspecified number of integers, determines

how many positive and negative values have been read, and computes the

total and average of the input values (not counting zeros). Your program

ends with the input 0. Display the average as a floating-point number. Here is

a sample run:

Enter integer value, the program exit if the input is 0.

1 2 -1 3 0The number of positives is 3

The number of negatives is 1

The total is 5

The average is 1.25



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Exercise 3: (cont)

Write C++ program for each problem statements. Implementmodular programming in your program.

Problem Statement 3:Finding the highest score

Write a program that prompts the user to enter the number of students

and eachstudents

score, and displays the highest score.

Problem Statement 4:Finding the highest and the lowest score

Write a program that prompts the user to enter the number of students

and each students score, and displays the highest and the lowest score.


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