structured programming introduction to c fundamentals

INF 130

STRUCTURED PROGRAMMING

(3 UNITS)

Instructor:

Dr. H. Bii / Mr. J Sigei

INTRODUCTION

Programming is a required skill today,

just like English and Maths.

It teaches a variety of skills that are

important in all kinds of professions: critical reading,

analytical thinking,

creative synthesis, and

attention to detail.

It provides immediate feedback, leading

to exploration, experimentation, and self-

evaluation.

What is programming?

Process of coming up with computer

programs.

But what is a program?

A PROGRAM is a set of instructions that a

computer can follow to do something.

Programming = process of coming up

with instructions that a computer can

follow to do something.

… What is programming?

As a process, it involves:

Understanding a problem for which a

solution is required;

Designing a solution;

Writing or coding the program in a

programming language;

Testing the code;

Correcting any errors (debugging); and

Maintaining the program.

… and Structured programming?

Programming that:

Enforces a logical structure on the

program to make it efficient and easier to

maintain/modify.

Implements modules (procedures /

functions), each fulfilling some function.

Uses basic programming constructs -

sequence, selection and iteration (no goto

statements in „spaghetti code‟).

Programming Language

Programming requires a programming

language:

a set of words, codes, and symbols that

allow a programmer to give instructions to

the computer.

Each language has rules (or syntax) for

writing the instructions.

… Programming Language

There are many programming

languages – so many! (like human

languages)

They may be classified (in many

ways, including) into THREE broad

categories:

Machine Language;

Assembly Language; and

High-level Languages.

Their Evolution

Machine LanguageMade up of streams of 1s and 0s.

Programs written as series of 1s and

0s is said to be in machine language:

… Machine Language

Machine language is the only language

understood by computer hardware.

Writing programs in machine language

is difficult and cumbersome –

instructions are difficult to remember.

The only language understood by computer

hardware is machine language.

… Machine Language

Each computer has its own machine

language; rules of language differ from

one computer hardware to another.

Note: Machine language is also

referred to as First Generation

programming language.

First generation programming

Language; also low-level languages

Symbolic / Assembly Language

Developed in 1950s to reduce

programmers‟ burden – by Grace Murray

Hopper, US naval officer.

She developed the concept of a special

computer program that would convert

programs into machine language.

… Symbolic / Assembly Language

The program mirrored the machine

languages using symbols, or mnemonics,

to represent the various machine

instructions.

The languages developed in this manner

were known as symbolic languages.

An assembler translates symbolic code

into machine language – thus Assembly

Language.

… Assembly language

High-Level LanguagesSymbolic language improved programming

efficiency, but still tedious and hardware focused.

High-level languages were developed to further

improve efficiency and change focus from

computer to the problem being solved.

High-level languages:

produce portable programs;

easier to learn;

require less time to write;

easier to maintain; and

provide better documentation.

… High-level language

Continued …

… example

Programs written in high-level languages have

English-like statements (and familiar math symbols)

and must be converted to machine language (1s and

0s).

The process of converting them is called compilation.

Examples of high-level languages are FORTRAN,

COBOL, C, BASIC, Pascal, ALGOL, and many

others.

Overview of some high-level languages

a) BASIC

Beginners‟ All-purpose Symbolic Instruction Code.

Developed by John Kemeny & Thomas Kurtz in

1964 – for beginners – easy to learn.

Example:5 REM Program to compute sum of 10 numbers

10 LET s = 0

20 FOR i=1 TO 10

30 READ n

40 LET s = s + n

50 NEXT i

60 PRINT "The sum of the given numbers ="; s

70 DATA 4, 20, 15, 32, 48

80 DATA 12, 3, 9, 14, 44

100 END

b) Pascal

Introduced in 1971 by Niklaus Wirth in Zurich becoming

the first language to fully embody structured

programming concepts.

Example:PROGRAM SUMNUM(INPUT, OUTPUT);

(* Program to Compute the sum of 10

numbers *)

(* Declaration of variables *)

VAR Sum, N :REAL;

VAR i :INTEGER;

BEGIN

Sum := 0;

FOR i := 1 TO 10 DO

BEGIN

READ (N);

Sum := Sum + N;

END;

WRITELN ('THE SUM OF GIVEN

NUMBERS =', SUM);

END

Assignment 1:

Read about and write short notes on the following

high-level languages:

FORTRAN;

COBOL;

ADA;

ALGOL; and

PL/1.

System and Program Development

System Development

An old programming proverb:

Resist the temptation to code.

Note

Program Development

Multistep process that requires that we:

Understand the problem – output

required; input available; steps to follow

in processing (algorithm).

Plan the logic of the solution (or

program). Three tools will help in this

task:

Flowcharts;

Pseudocode; and

Structure charts.

… Program Development

Code or write program statements in a

programming language e.g. BASIC, C,

Pascal. This may be done on paper.

Key the program into the computer

(use text editor).

Compile, test and debug the program.

Complete the documentation: charts,

listings, manuals.

... Programming Steps –

1) Understand the ProblemRead the problem or talk to & listen to the

person who posed the problem.

Identify the problem inputs, outputs, and

any additional requirements or constraints:

Inputs – data to work with;

Outputs – desired results;

Other Requirements/Constraints –

Relationships between variables, format of

results e.g. Table.

... Understand the Problem

Example:

Compute and display the total cost of

oranges given the weight of oranges

purchased and the cost per 1000g of

oranges.

... Understand the Problem

From the problem, we identify:

Compute and display the total cost of

oranges given the weight of oranges

purchased and the cost per 1000g of

oranges.

Inputs:

Quantity of oranges purchased (in Kgs);

Unit cost of oranges (in Kshs.).

... Understand the Problem

From the problem, we identify:

Compute and display the total cost of

oranges given the weight of oranges

purchased and the cost per 1000g of

oranges.

Outputs:

Total cost of oranges (in Kshs).

... Understand the Problem

Other requirements/constraints:

Total cost = Weight (Kgs) X Unit Cost

(Kshs).

The process we went thru (extracting

essential variables and their relationships)

is called ABSTRACTION.

... Understand the Problem

Exercises:

Read two numbers from the keyboard,

sum them up, and display the result.

Eldy surveyors want a program that

converts distances in miles to kilometres

and showing the result on screen.

2) Plan the logic of (Design) the solution

Involves developing a list of steps

(algorithm) to solve the problem.

Usually the most difficult part of problem-

solving process.

As noted above, 3 tools are important

here:

Structure charts;

Pseudocode; and

Flowcharts.

Structure Chart

Also called hierarchy chart.

It shows the functional flow through a

program – parts (modules) of a program

and how they are related e.g.

… structure chart

It is drawn before a program is written –

thus acting as an architectural blueprint –

more like a house plan.

In business world, once a structure chart

is completed, a structured walkthrough is

conducted – where a review panel is

taken through the structure to understand

how programmers plan to solve the

problem and attain the objectives they

set out to achieve.

… structure chart

Question 1:

Develop a structure chart for a program

that is meant to obtain two numbers

from a user, multiply the numbers and

show the result on screen.

Solution?

Multiply 2

numbers

Program

Print ResultCalculate

Product

Input first &

second

numbers

Pseudocode Is an English-like statement; part of program logic.

It describes what the program will do in precise

algorithmic detail e.g.

Pseudocode

English-like statements that follow a loosely defined syntax

and are used to convey the design of an algorithm.

Question 2:

Write a pseudocode for a program for calculating the

amount of tax (at 15% of value for property worth Kshs

100,000 and above, and 12% otherwise) of a property.

Assume that the user wants to determine taxes for more

than one property.

Question 3:

Write a pseudocode for a program for calculating

the cost of flooring the living areas (slide 33).

Reading:Do a literature search in the Library or on the Internet about pseudocodeas a design and documentation tool. Read and attempt the questions above.

Flowchart

Program design tool that uses standard

graphical symbols to represent logical

flow of data thru a function/program.

Its primary purpose is to show the design

of an algorithm.

… Flowchart

It frees a programmer from the syntax and

details of programming to concentrate on

details of the problem to be solved.

It gives a pictorial representation of an

algorithm – helps one to think of a

problem pictorially.

example Startv

Stop

Read

Length

Read

Width

Print Area

Calculate

Area = Length X

Width

example

Flowcharting Symbols:

Two basic categories:

1) Auxiliary symbols

enhance readability or functionality of a

flowchart.

They do not directly show instructions or

commands.

a) Terminators:

START STOP

b) Flow lines:

Rule: One entry/exit!

Rule: Start/Stop has one

Exiting/entering line!

… auxiliary symbols

c) Connectors:

n

Circle with number

in it.

2) Primary Symbols:

Show instructions or actions needed a problem presented in the algorithm.

They show all three structured programming constructs: sequence, decision, and repetition.

a) Sequence Symbols:

Sum ← x + y

i) Assignment

Statement:

ii) Input/Output

Statement:Read x

Startv

Stop

Read

Length

Read

Width

Print Area

Calculate

Area = Length X

Width

… sequence symbols:

iii) Module-call statement:

AVRG(ave, a, b, c)

Startv

Stop

Read (a)

Read (b)

Print

Average

Read (c)

AVRG(ave, a, b, c)

Flowchart for this

is elsewhere (below)

AVRG(rslt, x, y, z)v

Return

sum ← x + y + z

rslt ← sum/3

b) Selection statement symbols

Those for specifying conditional statements (that

allow execution of selected statements and

skipping of others).

There are 2 selection statements (decisions):

Two-way selection;

Multiway selection.

Condition Number > 10TF

T – to the right;

F – to the left;

NB: Not good practice to have any to bottom!

2-way:

… selection Startv

Stop

Read (a)

a > 10

TF

Write

(newnum)

newnum ← a - 10

NOTE: Only one statement (or

null) in each branch is allowed & it

may be a compound statement

… selection

Multiway selection:

Example (multiway selection)

Question 4:

Design an algorithm (flowchart) that reads an integer. If

the integer value is greater than 10, it subtracts 10 and

writes the original number and the result. If the number

is less than 10, it displays the message “That number is

less than 10”.

Question 5:

Design a flowchart for a program that reads a mark

between 0 and 100 and prints a corresponding letter

grade.

c) Looping Statements symbols

Iteration/repetition (for, while, do..while)

a) for

- Counting loop.

- pre-test, so body may

never be executed.

- good when number of

times to loop is known.

… for loop actions

Question 6:

Design a flowchart (or algorithm) for a program that

reads 20 numbers and print their sum.

? answer…

b) while

• Not a counting loop;

•Also pre-test loop – body

may not be executed.

•Good when number of

times to loop is not known.

Question 7:

Design a flowchart for a program that reads numbers from

the keyboard and prints their total. We don‟t know how

many numbers the user will input. However, all numbers

are positive numbers.

NOTE: first number is

read before the loop (i.e.

priming the loop)

c) do...while

• this is a post-test loop i.e. the

condition is tested at the end of

the loop.

•Body of the loop is executed at

least once

Question 8:

Design a flowchart for a program that reads and

processes numbers between 1 and 5. How it processes

the numbers is not important at this stage.

(num > 1)

&& (num < 5)

So far in Program Development …

Multistep process that requires that we:

Understand the problem – output required; input

available; steps to follow in processing (algorithm).

Plan the logic of the solution (or program). Three tools

will help in this task:

Flowcharts;

Pseudocode; and

Structure charts.

Code or write program statements in a programming

language e.g. BASIC, C, Pascal. This may be done on

paper.

Key the program into the computer (use text editor).

Test and debug the program.

Complete the documentation: charts, listings, manuals.

Exercises

Write a pseudocode and develop a flowchart for each of

the following problems:

1) Calculate the circumference and area of a circle (PI =

3.142).

2) Compute and display the letter grade of a student‟s

mark in a certain course.

3) Compute and print the net pay of an employee given

the number of hours worked and the hourly rate of

pay.

4) Convert the temperature given in degrees fahrenheit

to degrees celcius given that:

Degrees Celcius = (Degrees Fahrenheit – 32) * 5/9

Coding

Writing instructions in a programming language –

high-level language.

So we need to learn the language, its structure and

syntax.

Choice: C