1.Structured Programming(141)

7/25/2019 1.Structured Programming(141)

1/141


2/141


3/141

We often think that a computer program is nothing but a set of instructions. But it may not be true. It

does not do justice to the involved complexity of this simple idea. The idea of a program exists outside

any particular programming language, but we only get to see and experience it when it is expressed.

This makes it hard to separate the fundamental ideas from language features.

Given that a program is merely a list of instructions, one might think that all the fuss we make about it

is a little unjustified. However this is to underrate the complexity of this apparently simple idea. List of

instructions start out being simple. All you have to do is write down what is to be done at each step.

You start at step one, obey it and then move to step two. When step two is complete you move to

step three and so on.

The language, using which the program is written, is usually a little more precise than standard English

but it is nothing special in most cases it could usually do with being more precise but thats a

problem of another sort. The instructions are the program, the model builder is the computer and you

could even think of the actual model itself as the data that the program manipulates.


4/141


5/141


6/141


7/141


8/141


9/141


10/141


11/141

One of the most important aspects of problem solving is to clearly understand the

problem so that we can provide a correct solution. Asking the right set of questions is

the first step in getting the problem statement clear.

Once the problem is understood clearly, we can look for similar problems solved

elsewhere earlier so that the current problem also can be solved easily and quickly.

Analogy is an inference that, if things agree in some respects they probably agree in

others. Drawing a comparison in order to show similarity in some respect. E.g. the

working of the brain presents an interesting analogy to understand the operation of a

computer.

Means-ends analysis involves application of systems thinking .


12/141

Means-Ends Analysis (MEA): Application of systems thinking to planning whereby

the overall goal is broken down into objectives which in-turn are broken down into

individual steps or actions. MEA is based on the concept that 'every attainable end is

in itself a means to a more general end'.


13/141


14/141

The order of steps in an algorithm is also very important.


15/141


16/141


17/141

Note algorithm and flowchart are a different means to solve a problem. Since

flowchart is diagrammatic, users may find it more easier to understand than its

equivalent algorithm. Either an algorithm or flowchart is required to solve the

problem, not both. Objective is to solve the problem effectively rather than themeans.


18/141


19/141

Imagine a situation where step 1, 2 & 3 are mixed up. Will you get the expected

output? No. Hence it's very important that the steps are written in a proper sequence

to get the required output.


20/141

In a flowchart, we always need to ensure that all possible branches of a condition are

covered.


21/141


22/141

General approaches to the construction of efficient solutions to problems are of

interest because:

> They provide templates suited to solving a broad range of diverse problems.> They can be translated into common control and data structures provided by most

high-level languages.

> The temporal and spatial requirements of the algorithms which result can be

precisely analyzed.

Although more than one technique may be applicable to a specific problem, it is

often the case that an algorithm constructed by one approach is clearly superior to

equivalent solutions built using alternative techniques.


23/141


24/141

While algorithms are used for solving the problems from the user's perspective, it

cannot be directly fed or programmed into the computer for asking it to provide the

solutions. They are written in plain English which a normal human can understand.

In order to make a computer understand the algorithm, we need to program it in its

language. A programming language is a high-level language used by programmers to

write programs which then gets converted into machine language that the computer

can understand and execute.


25/141


26/141

; Example: Assembly language

; AX, DS, etc. are CPU registers

START :

MOV AX, @DATAMOV DS, AX

BEGIN :

MOV AX, 3H ; CLEAR SCREEN BY

INT 10H ; CHANGING VIDEO MODE

CALL DISP2

OPTION:

LEA DX,MSG32

CALL DISP1

CALL READCH ; READ CHOICE

AND AL, 0FH

CMP AL, 1 ; BRANCH TO APPROPRIATE

JNZ A ; MODULE DEPENDING ON

JMP CR_FILE ; THE CHOICE

A : CMP AL, 3


27/141

JZ VW_FILE

MOV AX, 4C00H ; EXIT PROGRAM

INT 21H


28/141

Power of high-level language (E.g. C, Java) is that they provide a few set of keywords

using which any complex problem can be solved.


29/141


30/141

Java is compiled to an intermediate "byte code" at compilation time. This is in

contrast to a language like C that is compiled to machine language at compilation

time. The Java byte code cannot be directly executed on hardware the way that

compiled C code can. Instead the byte code must be interpreted by the JVM (JavaVirtual Machine) at runtime in order to be executed. The primary drawback of a

language like C is that when it is compiled, that binary file will only work on one

particular architecture (e.g. x86). However with Java, given byte code can be

executed on any machine architecture provided appropriate is JVM is installed on that

computer.


31/141 3


32/141 3


33/141 3


34/141 3


35/141 3


36/141 3


37/141

During the maintenance phase, apart from enhancing already implemented programs

which may arise due to changing business scenarios, some defects which might have

gone undetected during the testing phase also may be fixed.

3


38/141

Answer: Keep changing the problem statement

3


39/141

Answer: Includes set of implicit steps

3


40/141

Answer: Greedy algorithm

Transform-and-conquer

3


41/141

Answer: Non-procedural language

4


42/141 4


43/141 4


44/141

Identifiers or variable names can contain alphabets, digits and few special characters

like $ and _ (underscore). Some programming languages may allow other special

characters also. COBOL allows minus (-) sign in variable names. However, no variable

name can start with a number and have white space (blank, tab or newline character)in them. Variable names may have maximum length which is again dependent on the

programming language. Some valid variable names:

account_number

fixed_price1

customerName

Invalid variable names:

1password

product id

ticket-price

4


45/141

First step in creating appropriate data is to know what kind of data to create i.e. data

literacy. Create variables based on the need. Creating too many and not using them

later is not going to help solve the problem easily.

4


46/141 4


47/141 4


48/141

The main problem with persistence arises when you assume that a variable has a

longer persistence than it really does. Shorter the persistence the better it is for the

program.

4


49/141

The time at which the variable and its value are bound together is the binding time of

the variable. Later the binding time, better the programming. Binding while writing

the code should be avoided for it hard-codes the values in the program; it induces

inflexibility into the program.Assignment during compile time e.g. Assignment of macro values, constants are done

during compile time.

4


50/141 4


51/141 5


52/141

Naming a variable too short like i, j, k, etc. should be avoided; on the other hand

having too long a name also (e.g. customers_savings_bank_account_number) would

pose difficulty during programming and maintenance phase later.

It is very important that we follow appropriate naming convention (as set by the

project) for better programming.

5


53/141 5


54/141

Some compilers like C and Java are smart enough while evaluating expression

involving such logical operators. For e.g. in comparisons like "if a > 10 AND b < 20", if

the value of a is 10 or less, it will not go to evaluate the expression if b < 20 because,

one 'false' condition in an AND operator, will result in whole expression evaluating to'false'. It's like multiplying many numbers with zero, answer is always zero.

Similar explanation holds good for OR also. In expression, if a > 10 OR b < 20, if value

of a is more than 20, the whole expression becomes true irrespective of whether b = 20.

5


55/141 5


56/141

It is quite unlikely that a program will always have a sequential flow i.e. executing

each statement starting from line #1 one-by-one till the end. Based on the various

conditions and situations, few statements get executed many times, few of them may

get skipped, few of them may never get executed (e.g. rare error conditions). It isduring the program design that we decide about such flow based on the

requirements of the program.

5


57/141

Conditional constructs are one of the very important constructs in a program that

make a make-or-break kind of decision. Some examples that might require if else

ladder are deciding the grade based on the marks range, deciding the tax based on

the income range, increment calculation based on no. of years of service and similarsituations.

'case' statement replaces multiple 'if' statements provided they use equality

operators (if a = 1 , if a = 2, ). Some examples include: menu selection, salary

decision based on employee grade, tax calculation based on state code , etc.

5


58/141 5


59/141 5


60/141 5


61/141


62/141


63/141


64/141


65/141


66/141


67/141


68/141

Looping construct is the one which makes the users to get the best use of power of a

computer. Based on the given value the program can be made to execute the same

set of instructions (possibly with different values) 10, 100, 1000, 10000 and even

beyond!

However, one side effect of looping is that it may go for 'infinite loop' if the loop exit

condition is not properly checked so that the loop never ends. This however can be

solved with little more analysis, debugging the program and taking experts' help.


69/141


70/141


71/141 7


72/141 7


73/141

Use do .. while loop when you need to run through the loop at least once like

showing a list menu of menu items.

7


74/141 7


75/141 7


76/141 7


77/141

Entering the loop:

Enter from one location

Put initialization code before the loop

Decide between for and while loops

Inside the loop

Use bracket sets to group the loop statements even if there is only one statement

in the loop

Avoid empty loops

Keep loop housekeeping part either at the beginning or end of the loop (E.g.

increment, etc.)

Assure that the loop ends!

Do not play around with for loop index values

Exiting the loop

Use break statements if it has to be exited early

May have to use multiple break statements in case of nested loops

Use continue to skip the loop for certain iterations

Use extra caution while using break and continue statements

7


78/141

Since 'goto' makes the control to flow unconditionally to any location inside the

program, it's considered as an unprofessional programming practice in languages like

C, C++, etc. However, it would be very difficult to write FORTRAN programs without

using gotos.

7


79/141

Answer: Its life span

7


80/141

Answer:what data gets stored in it

7


81/141

Answer: it is an infinite loop

8


82/141

Answer: No output

8


83/141 8


84/141

Arrays are used for storing homogeneous data. E.g. marks of students, employee

numbers, salaries of employees, names, etc. Array name is the index to the first

element of the array. Such arrays are called static arrays. They have limitation that

their sizes needs to be specified while declaring them. If all locations of an array arenot used, the memory space consumed by them is going to be wasted and cannot be

used by other programs or variables till the program exits. Hence the program has to

be designed in such a way to make efficient use of all elements of an array.

Programs involving arrays usually have looping statements to process the array

elements. Loop will execute as many no. of times as the no. of elements in the array,

to process each element in every iteration.

8


85/141

It's during the declaration of the array, the memory space is allocated to it. An integer

of 100 elements would require 200 bytes of memory space (assuming each integer

requires 2 bytes of space).

8


86/141

In this case numArray with 5 elements will be initialized with those values. Note that

in most of the programming languages the array subscript i.e. the index to access

individual array element, starts from 0. Hence array of size N, will have the max index

N 1. Accessing the array element beyond this index may result in an error or will notgive the expected result.

Initializing the array during declaration itself is a good practice for it requires a

looping structure to initialize it at later time. Programming language C, Java, etc. have

library routines to initialize array elements without using loop statements. However,

initializing the array during declaration is better.

8


87/141 8


88/141

As an example, a single-dimensional array may be used to store marks of a student

stores scored in various subjects. Similarly, a two-dimensional array may be used to

store marks of multiple students in various subjects. Continuing with this example, a

three-dimensional array can be created to store marks of multiple students in varioussubjects in different examinations. However, going beyond this will make the program

more complex and very difficult to maintain and understand.

8


89/141

Though multi-dimensional array is shown in a tabular structure, its elements however

are stored in sequential manner in the memory. Specific element can be accessed by

an arithmetic expression using its row and column size.

Element (i, j) can be accessed using expression, i * column size + j.

For e.g. referring to the 2-dimensional array above whose column size is 4,

numArray[3][2] = 3 * 4 + 2 = 14th element starting from 0 i.e. 5 (last row, column

subscript [2]).

8


90/141 8


91/141

While static arrays require their size to be decided during compile time (i.e. while

creating the program), a pointer makes it dynamic so that the size can be decided

during run time.

The limitation of static arrays, their size to be decided during declaration, is overcome

by pointers. They can be allocated allocate memory dynamically during run time (late

binding). Once the work is complete, the memory can be de-allocated i.e. released

back to the system. This again is a limitation in static arrays, which cannot be done

unless the program exits.

9


92/141

Pointer can be similar to a librarian having an index of book titles along with their

location i.e. shelf no. on which it is kept. If somebody asks for a particular book, she

can refer to the index, go to the exact shelf where the book is placed to access it. It

will save a lot of time that would otherwise have spent in searching for it arbitrarily.In this case, each index is pointing to exactly one location. If there is any change in

the library layout, librarian will have to change the index values of books relocated.

9


93/141 9


94/141 9


95/141

You would typically ask a plumber who fixed your piping problem in your home, the

exact cause of the problem. It would help avoid the same problem recurring in future.

Just an explanation of 'there was some problem' would not satisfy you. Similarly, it's

very important that we communicate the exact error in the program to the end-userusing appropriate language. (Just like a doctor explaining the patient about an

operation that he is going to perform on the patient without using complex medical

terms, still making the patient understand what is the actual problem and why it's

required)

9


96/141

Answer: countArray[4][3] = 43;

9


97/141

Answer: 10

9


98/141

Answer: Pointer is uninitialized

9


99/141 9


100/141 9


101/141

Library routines provided by high-level languages hide implementation details;

programmers do not get to see their implementation details (which is certainly not

required). Appropriate inputs and outputs are defined so as to make their appropriate

use.

10


102/141

Think of a routine as a piece in a jig-saw puzzle. There are common pieces and there

are specific ones which fit the corners. A routine is independent of the caller i.e. any

changes done in the calling program will not result in changes to the routine.

Similarly, changes in the implementation details of a routine may not require achange in the calling program.

Routines should be robust enough to handle error situations like invalid inputs or data

errors. Errors in the routines should not abruptly end the program. They should be

appropriately communicated to the calling program so that the calling program would

take appropriate action based on the severity of the error.

10


103/141

In languages like C, C++, Java, etc. every subprogram is a function (or method). They

have to return a value at the end or they should be declared as 'void functionName()'

if they do not return any value.

10


104/141 10


105/141 10


106/141

Not all programming languages may have a separate subprogram type called

subroutine. However, subroutine and function are referred in a similar context in

general.

10


107/141

Parameters provide the interface to the function i.e. they make the function more

generic. Carrying out same set of operations but on a different data set. For e.g.

salary calculation method is same for all employees; however, inputs will differ for

every employee.

Having too many parameters to a function would make it difficult to call and

maintain, on the other hand having too less or no parameters may make it more

specific. This decision has to be taken during design time based on the requirements

of the function.

10


108/141 10


109/141 10


110/141 10


111/141

Answer: none of these.

1


112/141

Answer: false

1


113/141

Answer: pass by reference

1


114/141 1


115/141 1


116/141 1


117/141

An interactive Calculator program may be designed to have independent functions to

carry out required mathematical function. Advantage with this is that, functions can

be independently modified without causing major impact to any other modules.

Addition of new function (for e.g. square root) can also done easily.

1


118/141 1


119/141

Answer: All of these

1


120/141 1


121/141 1


122/141

Naming convention: Using variable name minimum_balance rather than mb. Using

function name calculate_interest rather than calcint

Indentation: Aligning code lines as per the block / loop they belong to. (Refer to

example programs)Comments: Enough lines of appropriate comments to make the program more

understandable. Assume it's part of the code as if without it compiler may give an

error.

Declarations: Logically grouping declarations and initializations.

Statements: Logically grouping the statements. Not too long statement lines. Wrap to

next line if the line goes beyond 80-90 characters to avoid horizontal scrolling.

Whitespaces: Space, tab & new lines. To logical group things in the program. Do not

too many unnecessary whitespaces.

1


123/141 1


124/141

Useful error messages: As an example, if the user has entered invalid CVV (Card

Verification Value) code for his credit card no., it's logical to display error message

saying, "You've entered invalid CVV code" rather than saying "Error in credit card no.".

Dead code are such code lines which never get executed. While most of the

compilers nowadays detect them and give warning messages about it, they may not

be able to do so if it's due to some logical error. For e.g. condition if (loggedInUserId

= "") may never be true if this condition is checked in a module which would get

executed once the user logs into the application.

1


125/141 1


126/141 1


127/141 1


128/141

In order to reach your destination very quickly in a metropolitan city rushing through

a heavy traffic, you need to start early or plan accordingly. None of the tricks of

showing different driving stunts, honking, overtaking, blocking others, etc. will take

you to the destination on time if you've started late. In fact, it would make theproblem much worse.

This applies to code tuning also. Clear and specific requirements, followed by an

effective design, are a good prerequisites to proper coding. The programmer should

make the best of use of good design in writing the effective code. It's the

programmer's responsibility to convert this design into a correct, tuned code.

1


129/141 1


130/141 1


131/141 13


132/141 13


133/141 13


134/141 13


135/141 13


136/141

Answer:int c = a + b;

for (i = 0; i < c; i++)

myTbl[i] = yrTbl[i] * c;

13


137/141

Answer: break;

13


138/141

Answer: Make sure that the design is correct

13


139/141 13


140/141 13


141/141

Documents

1.Structured Programming(141)