unit 7 - object oriented programming / c++

8/6/2019 Unit 7 - Object Oriented Programming / C++

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Functions (Part I) QF002/7/1

UNIT 7

General Objective : To understand and apply the fundamental

concept of functions in C++ programming.

Specific Objective : At the end of the unit you should be able to :-

Describe the declaration of functions. Explain how to declare and initialize functions. Use functions in a program. Write and design a simple functionof a program.

OBJECTIVES

FUNCTIONS

(Part I)


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7.0 Introduction

As shown in figure 7.1 below, when a function call is made, the program execution jumps to the function and finishes the task

assigned to the function. Then the program execution resumes

after the called function returns.

INPUT

To make large program manageable, programmers

modularize them into subprograms. These subprograms are

called functions. They can be compiled and tested separately

and being reused in different programs. This modularization

is one of the characteristics of successful object -oriented

software.

I see


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7.1 Standard Header Files C++ provides numerous predefined functions. These functions

are stored in what are known as standard header files

(with extension .h)

Figure 7.2 shows the location of the HeaderFiles in Turbo C++Programming.

Start

Function Call

Function

Execution

Function

Return

End

Program

ExecutionFlow

Figure 7.1: A Program Execution Jumps To An Invoked Function

When A Function Call Is Made

noteA function is declared with a function prototype, which describes the

return value, the function name, and its parameter types. A function

can optionally be declared inline. A function prototype can also

declare default variables for one or more of the parameters.


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Before you can use any of the functions contained in a headerfile, you must include the header file in your program. You can

do this by using the #include preprocessor directive place before

the function main().

The preprocessor directive has the general form#include < filename>

Figure 7.3 below shows a simple program that uses the standardheader files.

#include < iostream.h>

#include < math.h>#include < string.h>

{:::::::::::

:::::::::::

}

Figure 7.3 :Simple Program That Uses The Standard Header Files.

Figure 7.2 : Location Of The Header Files.


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iostream.h - The name iostream.h stands for input/outputstream header file. The basic I/O objects contained in this header

files are cin for console input (the keyboard) and cout forconsole output (the screen). cin operator is used with the

operator >> while cout is used with operator


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7.1.2 string.h string.h - This header file contains several string

manipulation functions. A partial list is given in Figure 7.3 .

Here, we will only highlight some of these functions.

FUNCTION RETURN VALUE

iIsalnum ( c )

isalpha ( c )

isascii ( c )

iscntri ( c )

isdigit ( c )

isgraph ( c )

islower ( c )

isodigit ( c )

isprint ( c )

isunct ( c )

isspace ( c )

isupper ( c )

isxdigit ( c )

toascii ( c )

tolower ( c )

toupper ( c )

Non-zero if c is alphanumeric; 0 otherwise

Non-zero if c is alphabetic; 0 otherwise

Non-zero if c is an ASCII character; 0 otherwise

Non-zero if c is a control character; 0 otherwise

Non-zero if c is a digit; 0 otherwise

Non-zero if c is a graphic character space excluded; 0 otherwise

Non-zero if c is a lowercase letter; 0 otherwise

Non-zero if c is an octal digit; 0 otherwise

Non-zero if c is a printable character; 0 otherwise

Non-zero if c is a punctuation character; 0 otherwise

Non-zero if c is a space, tab, form feed or newline character; 0 otherwise

Non-zero if c is uppercase letter; 0 otherwise

Non-zero if c is a hexadecimal digit; 0 otherwise

ASCII equivalent

Lowercase equivalent of c if it is a letter; unchanged otherwise

Uppercase equivalent of c if it is letter; changed otherwise

Figure 7.2 : List Of Function In Ctype.H

The header files that are

required by the #include

directive, like iostrem.h.


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Figure 7.3: Header File That Contains Several String Manipulation

Functions.

FUNCTION ACTION

stsrcat ( ) Appends one string to another

strchr ( ) Scans a string for the first

occurrence of a given character

strcmp ( s1, s2 ) Compares one string to another

strcmpi ( s1, s2 ) Compares one string to another

without case sensitivity

strcpy ( s1, s2 ) Copies one string into another

strlen ( s ) Calculates the length of a string

strlwr ( ) Converts uppercase letters in a

string to lowercase

strrev ( s ) Reverses the string

strset ( s, c ) Sets all characters in a string to

given character

strstr ( ) Scans a string for the

occurrence of a given substring

strupr ( ) Converts lowers letter in a

string to uppercase


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The function strlen ( ) calculates the length of string. It takesthe form

strlen (string)

Example:

Cout s2

7.1.3 stdlib.h stdlib.h - The standard library header file contains several

miscellaneous functions. Figure 7.4 gives a partial list o f

these functions. The argument type varies depending on the

function. They are void, int, char or some other types.


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Figure 7.4 Standard Library Header File Contains Several Miscellaneous

Functions

7.2 Defining Header

Before you can use a function in a program, you must define itfirst. A function definition takes the form Retur_type

function_name (parameter-list) as follows:

FUNCTION ACTION

abort ( ) Terminates program without closing files and buffers

atof( s ) Converts (string) s to a float (double)

abs ( I ) Converts to the absolute value of i

atoi ( s ) Converts s to an integer

atol ( s ) Converts s to a long integer

exit ( s ) Terminate program after closing all files and buffers

labs ( l ) Takes the absolute value of a long integer

rand( ) Returns a random positive integer between 0 and

RAND_MAX (327676)

strset ( s, c ) Initialize the random number generator rand( )

{

variable

declaration

statements

return expression

}


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where

y return type is any valid C++ date typey function_name is any valid C++ identifiery parameter-list is a list of parameter separated by commasy variable declaration is a list of variables declared within the

function

y return is a C++ keywordy expression is the value returned by the function

The return_type (placed before the function_name) indicatesthe type of value that the function will return when the return

statement(s) in the function is executed. The return value (given

by the ex pression in the return statement) may be of any valid

data type: int, double, char, etc. If you do not specify its type,

the function is assumed to return an integer value by default.

It is also possible that a function may not return any value to thecalling program function. In this case we say the function returns

a value of type void. If the return type is void, the return

statement may be dropped as we have done in our programs.

The function_name is the name of the function and the parameter-list is a list of parameter (sometimes called formal

parameters or dummy variables), separated by commas. The

parameter type tells what value the parameter will receive if the

function is invoked (called).


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Every parameter in the parameter-list must include its name andtype. Thus the parameter-list for a function declaration takes the

form;Type var_1, type var_2, ... , type var_N

What are the differences

between the function prototype

and the function definition?

The function prototype declares the function; the

definition defines it. The prototype ends with a

semicolon; the definition need not. The declaration

can include the keyword inline and default values

for the parameters; the definition cannot. The

declaration need not include names for the

parameters; the definition must.


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Test your comprehension before continuing the next input.

Check your answers on the next page.

7.1. If a function is not returning any value to the calling programfunction we say the function returns a value of type

___________.

7.2. Usually every parameter in the parameter-list must include its____________ and __________.

7.3. Normally in a program we must _______________ a functionbefore we can use it.

7.4. The return_type which placed before the _______________indicates the type of value that the function will return when the

return statement(s) in the function is executed.

Activity 7a


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Make sure you have tried to answer all the questions given. You can

check your answers with the answers below .

7.1. void7.2. name , type7.3. define7.4. function_name

Feedback7a


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You are approaching success, please answer the questions below. If you

have any problems, please discuss it with your lecturer. Wish you good

luck and all the best.

Question 7-1

a. C++ provides a set of header files containing commonly usedfunctions that programmers can use without having to write any code

for them. What are those functions called?

b. To simplify programming C++ provides a set off predefined function.Where are these functions stored?

c. What does iomaip.hcontain?d. What is the function of strlwr()?e. The header file contains several string manipulation functions. List

down 3 of them.

f. Before you can use a function in a program, you must define it first. Afunction definition takes the form as below:

{

variable declaration

statements

return expression

}

What is the ex pression for ?

Self-Assessment


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Make sure you have tried to answer all the questions given. You can check

your answers with the answers below.

Answer 7 - 1

a. These functions are called built -in, pre-defined or standard libraryfunction.

b. These functions are stored in header files.c. The iomaip.h header file contains function for formatting your output.d. It converts uppercase letters in a string to lowercase.e.

i. stsrcat ( )ii. strchr ( )

iii. strlen ( s )

f. The expression is the value returned by the function.

FeedbackOn Self-Assessment

CONGRATULATIONS

May success be withyou always..

unit 7 - object oriented programming / c++

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