Structured programming Unit-1-Introduction-to-C-Programming.pptx

Er. Nipun Thapa
Unit 1 : Introduction to C Programming
Nipun Thapa/BIM_C/Unit 1
1 3/29/22

1.1. Introduction and History
⚫ C is a programming language developed at AT & T’s Bell Laboratories of
USA in 1972. It was designed and written by a man named Dennis Ritchie.
⚫ In the late seventies C began to replace the more familiar languages of that
time like PL/I, ALGOL, etc
⚫ It was initially designed for programming UNIX operating system. Now the
software tool as well as the C compiler is written in C. Major parts of
popular operating systems like Windows, UNIX, Linux is still written in C.
⚫ This is because even today when it comes to performance (speed of
execution) nothing beats C.
⚫ Moreover, if one is to extend the operating system to work with new
devices one needs to write device driver programs. These programs are
exclusively written in C.
⚫ C seems so popular is because it is reliable, simple and easy to use. Often
heard today is – “C has been already superceded by languages like C++, C#
and Java.
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1.1. Introduction to
Programming Language
Fig. 1.1. Steps in C program
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1.1. Introduction to
Programming Language
⚫ Learning C is similar and easier.
⚫ Instead of straight-away learning how to write programs, we
must first know what alphabets, numbers and special
symbols are used in C, then how using them constants,
variables and keywords are constructed, and finally how
are these combined to form an instruction.
⚫ A group of instructions would be combined later on to form a
program.
⚫ So a computer program is just a collection of the instructions
necessary to solve a specific problem.
⚫ The basic operations of a computer system form what is
known as the computer’s instruction set. And the approach or
method that is used to solve the problem is known as an
algorithm.
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1.2. Types of Programming Language
Programming Languages
Low Level Language High Level Language
Procedure Oriented
Language
Problem Oriented Language
Natural Language
Assembly
Language
Machine
Language
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So for as programming language concern these are of
two types.
⚫Low level language
⚫High level language
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1. Low level language:
⚫ Low level languages are machine level and assembly level
language.
⚫ In machine level language computer only understand digital
numbers i.e. in the form of 0 and 1. So, instruction given to
the computer is in the form binary digit, which is difficult to
implement instruction in binary code.
⚫ This type of program is not portable, difficult to maintain and
also error prone. The assembly language is on other hand
modified version of machine level language.
⚫ Where instructions are given in English like word as ADD,
SUM, MOV etc. It is easy to write and understand but not
understand by the machine. So the translator used here is
assembler to translate into machine level.
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2. High level language:
⚫These languages are machine independent, means
it is portable. The language in this category is
Pascal, Cobol, Fortran etc.
⚫High level languages are understood by the
machine. So it need to translate by the translator
into machine level.
⚫A translator is software which is used to translate
high level language as well as low level language in
to machine level language.
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1.3. Language Processor
Three types of translator are there:
⚫Compiler
⚫Interpreter
⚫Assembler
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1. Compiler
⚫ The language processor that reads the complete source program written in
high level language as a whole in one go and translates it into an equivalent
program in machine language is called as a Compiler.
⚫ Example: C, C++, C#, JavaIn a compiler, the source code is translated to
object code successfully if it is free of errors. The compiler specifies the
errors at the end of compilation with line numbers when there are any
errors in the source code. The errors must be removed before the compiler can
successfully recompile the source code again.
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2. Assembler
⚫ The Assembler is used to translate the program written in
Assembly language into machine code.
⚫ The source program is a input of assembler
that contains assembly language instructions.
⚫ The output generated by assembler is the object code or
machine code understandable by the computer.
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3. Interpreter
⚫ The translation of single statement of source program into machine
code is done by language processor and executes it immediately
before moving on to the next line is called an interpreter.
⚫ If there is an error in the statement, the interpreter terminates its
translating process at that statement and displays an error
message.
⚫ The interpreter moves on to the next line for execution only after
removal of the error.
⚫ An Interpreter directly executes instructions written in a
programming or scripting language without previously converting
them to an object code or machine code.
Example: Perl, Python and Matlab.
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COMPILER INTERPRETER
1. A compiler is a program which coverts
the entire source code of a programming
language into executable machine code
for a CPU.
1. interpreter takes a source program and
runs it line by line, translating each line
as it comes to it.
2. Compiler takes large amount of time to
analyze the entire source code but the
overall execution time of the program is
comparatively faster.
2. Interpreter takes less amount of time to
analyze the source code but the overall
execution time of the program is slower.
3. Compiler generates the error message only
after scanning the whole program, so
debugging is comparatively hard as the
error can be present any where in the
program.
3. Its Debugging is easier as it continues
translating the program until the error is
met
4. Generates intermediate object code. 4. No intermediate object code is generated.
5. Examples: C, C++, Java 5. Examples: Python, Perl
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1.4. Program Errors
⚫ Error is an illegal operation performed by the user which results in
abnormal working of the program.
⚫ Programming errors often remain undetected until the program
is compiled or executed.
⚫ Some of the errors inhibit the program from getting compiled or executed.
Thus errors should be removed before compiling and executing.
⚫ The most common errors can be broadly classified as follows.
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1.4. Program Errors
15
1. Syntax errors:
⚫ Errors that occur when you violate the rules of writing C/C++ syntax are
known as syntax errors. This compiler error indicates something that must be
fixed before the code can be compiled. All these errors are detected by
compiler and thus are known as compile-time errors. Most frequent syntax
errors are:
⚫ Missing Parenthesis (})
⚫ Printing the value of variable without declaring it
⚫ Missing semicolon like this:// C program to illustrate
// syntax error
#include<stdio.h>
int main()
{
int x = 10;
int y = 15;
printf("%d", (x, y)) // semicolon missed
retutn 0;
} Error: 3/29/22

1.4. Program Errors
16
2. Run-time Errors :
⚫ Errors which occur during program execution(run-time) after
successful compilation are called run-time errors. One of the most
common run-time error is division by zero also known as Division
error. These types of error are hard to find as the compiler doesn’t
point to the line at which the error occurs. For more understanding
run the example given below.
#include<stdio.h>
int main()
{
int n = 9, div = 0;
// wrong logic
// number is
divided by 0,
// so this
program
abnormally
terminates
div = n/0;
} 3/29/22

1.4. Program Errors
3. Logical Errors :
⚫ On compilation and
execution of a program, desired
output is not obtained when
certain input values are given.
These types of errors which
provide incorrect output but
appears to be error free are
called logical errors. These are
one of the most common
errors done by beginners of
programming. These errors
solely depend on the logical
thinking of the programmer
and are easy to detect if we
follow the line of execution
and determine why the
program takes that path of
execution.
// C program to illustrate
// logical error
int main()
{
int i = 0;
// logical error : a semicolon after
loop
for(i = 0; i < 3; i++);
{
printf("loop
"); continue;
}
getcha
r(); return
0;
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}

1.5. Features of good Program
⚫ Every computer requires appropriate instruction set
(programs) to perform the required task.
⚫ The quality of the processing depends upon the given
instructions.
⚫ If the instructions are improper or incorrect, then it is
obvious that the result will be superfluous.
⚫ Therefore, proper and correct instructions should be
provided to the computer so that it can provide the
desired output.
⚫ Hence, a program should be developed in such a way
that it ensures proper functionality of the computer. In
addition, a program should be written in such a manner
that it is easier to understand the underlying logic.
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⚫A good computer program should have following
characteristics:
1. Portability
2. Readability
3. Efficiency
4. Structural
5. Flexibility
6. Generality
7. Documentation
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1. Portability:
⚫ Portability refers to the ability of an application to run
on different platforms (operating systems) with or
without minimal changes.
⚫ Due to rapid development in the hardware and the
software, nowadays platform change is a common
phenomenon.
⚫ Hence, if a program is developed for a particular
platform, then the life span of the program is severely
affected.
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2. Readability:
⚫ The program should be written in such a way that it
makes other programmers or users to follow the logic of
the program without much effort.
⚫ If a program is written structurally, it helps the
programmers to understand their own program in a
better way.
⚫ Even if some computational efficiency needs to be
sacrificed for better readability, it is advisable to use a
more user-friendly approach, unless the processing of an
application is of utmost importance.
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3. Efficiency:
⚫ Every program requires certain processing time and
memory to process the instructions and data.
⚫ As the processing power and memory are the most
precious resources of a computer, a program should be
laid out in such a manner that it utilizes the least
amount of memory and processing time.
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4. Structural:
⚫ To develop a program, the task must be broken down
into a number of subtasks.
⚫ These subtasks are developed independently, and each
subtask is able to perform the assigned job without the
help of any other subtask.
⚫ If a program is developed structurally, it becomes more
readable, and the testing and documentation process
also gets easier.
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5. Flexibility:
⚫ A program should be flexible enough to handle most of
the changes without having to rewrite the entire
program.
⚫ Most of the programs are developed for a certain period
and they require modifications from time to time.
⚫ For example, in case of payroll management, as the time
progresses, some employees may leave the company
while some others may join.
⚫ Hence, the payroll application should be flexible enough to
incorporate all the changes without having to
reconstruct the entire application.
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6. Generality:
⚫ Apart from flexibility, the program should also be
general. Generality means that if a program is developed
for a particular task, then it should also be used for all
similar tasks of the same domain.
⚫ For example, if a program is developed for a particular
organization, then it should suit all the other similar
organizations.
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7. Documentation:
⚫ Documentation is one of the most important
components of an application development.
⚫ Even if a program is developed following the best
programming practices, it will be rendered useless if the
end user is not able to fully utilize the functionality of
the application.
⚫ A well-documented application is also useful for other
programmers because even in the absence of the author,
they can understand it.
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1.6. Introduction to Program Technique
⚫ C is a general-purpose, procedural, imperative computer
programming language developed in 1972 by Dennis M. Ritchie at
the Bell Telephone Laboratories to develop the UNIX operating
system.
⚫ C is the most widely used computer language.
⚫ It keeps fluctuating at number one scale of popularity along with
Java programming language, which is also equally popular and
most widely used among modern software programmers.
Nipun Thapa-BCA-C-Unit 2
27

1.6. Top down and Bottom up Approach
Top down Approach
⚫ The basic task of a top-down approach is to divide the
problem into tasks and then divide tasks into smaller
sub-tasks and so on.
⚫ Each part of it then refined into more details, defining it in
yet more details until the entire specification is
detailed enough to validate the model.
⚫ It break the problem into parts, Then break the parts
into parts soon and now each of part will be easy to do.
28

Top down Approach
⚫ C programming language supports this approach
for developing projects.
⚫ It is always good idea that decomposing solution into
modules in a hierarchal manner.
⚫ In this approach, first we develop the main module and
then the next level modules are developed.
⚫ This procedure is continued until all the modules are
developed.
29

Top down Approach
Program
X Y Z
X1 X2 X3 Y1 Y2 Z1 Z2
30

Top down Approach
Advantages:
⚫ Breaking problems into parts help us to identify what needs to be
done.
⚫ At each step of refinement new parts will become less complex and
therefore easier to solve.
⚫ Parts of solution may turn out to be reusable.
⚫ Breaking problems into parts allows more than one person to solve the
problem.
31

Bottom-Up Design Model:
⚫ In this design, individual parts of the system are specified in details.
⚫ The parts are the linked to form larger components, which are in
turn linked until a complete system is formed.
⚫ This approach is exactly opposite to the top-down approach.
⚫ In this approach, bottom level modules developed first (Lower level
module developed, tested and debugged).
⚫ Then the next module developed, tested and debugged.
⚫ This process is continued until all modules have been completed.
⚫ This approach is good for reusability of code.
⚫ Object oriented language such as C++ or java uses bottom
up approach where each object is identified first.
32

Program
X Y Z
X1 X2 X3 Y1 Y2 Z1 Z2
33

Advantage:
⚫ Make decisions about reusable low level utilities then decide how
there will be put together to create high level construct.
⚫ Contrast between Top down design and bottom up design.
34

S.NO. TOP DOWN APPROACH BOTTOM UP APPROACH
1. In this approach We focus on breaking up the
problem into smaller parts.
In bottom up approach, we solve smaller
problems and integrate it as whole and
complete the solution.
2.
Mainly used by structured programming
language such as COBOL, Fortan, C etc.
Mainly used by object oriented programming
language such as C++, C#, Python.
3.
Each part is programmed separately
therefore contain redundancy.
Redundancy is minimized by using data
encapsulation and data hiding.
4.
In this the communications is less among
modules.
In this module must have communication.
5.
It is used in debugging, module
documentation, etc.
It is basically used in testing.
6.
In top down approach, decomposition takes
place.
In bottom up approach composition takes
place.
7.
In this top function of system might be hard
to identify.
In this sometimes we can not build a
program from the piece we have started.
8. In this implementation details may differ. This is not natural for people to assemble.
35

A C program is divided into different
sections.
There are six main sections to a basic c program.
The six sections are,
⚫Documentation
⚫Link
⚫Definition
⚫Global Declarations
⚫Main functions
⚫Subprograms
36
1.7.Strucuted Programming

Figure: Basic Structure Of C Program
37

1. Documentation Section
⚫ The documentation section is the part of the program where the
programmer gives the details associated with the program.
⚫ It usually gives the name of the program, the details of the author and
other details like the time of coding and description. It gives anyone
reading the code the overview of the code.
Example
/**
* File
Nam
e:
Hello
worl
d.c
* Auth
or:
Mant
han
Naik
38

2. Link Section
⚫ This part of the code is used to declare all the header
files that will be used in the program.
⚫ This leads to the compiler being told to link the header
files to the system libraries.
Example
#include<stdio.h>
Moving on to the next bit of this
basic structure of a C program
article,
39

3. Definition Section
⚫ In this section, we define different constants. The
keyword define is used in this part.
Example
#define PI=3.14
Moving on to the next bit of this basic structure of a C
program article,
40

4. Global Declaration Section
⚫ This part of the code is the part where the global variables are
declared.
⚫ All the global variable used are declared in this part.
⚫ The user-defined functions are also declared in this part of the
code.
Example
float area(float r);
int a=7;
Moving on to the
next bit of this basic
structure of a C
program article,
41

5. Main Function Section
⚫ Every C-programs needs to have the main function. Each main function
contains 2 parts. A declaration part and an Execution part. The declaration
part is the part where all the variables are declared. The execution part
begins with the curly brackets and ends with the curly close bracket. Both the
declaration and execution part are inside the curly braces.
Example
int main(void)
{
int a=10; printf("
%d", a); return
0;
}
Moving on to the
next bit of this
basic structure of
a C program
42

6. Sub Program Section
⚫All the user-defined functions are defined in
this section of the program.
Example
int add(int a, int b)
{
return a+b;
}
43

44

Features of structured programming
⚫ The structured program consists of well structured and separated
modules.
⚫ But the entry and exit in a Structured program is a single-time
event.
⚫ It means that the program uses single-entry and single-
exit elements.
⚫ Therefore a structured program is well maintained, neat and clean
program.
⚫ This is the reason why the Structured Programming Approach is
well accepted in the programming world.
45

Advantages of Structured Programming
Approach:
⚫ Easier to read and understand
⚫ User Friendly
⚫ Easier to Maintain
⚫ Mainly problem based instead of being
machine based
⚫ Development is easier as it requires less effort
and time
⚫ Easier to Debug
⚫ Machine-Independent, mostly.
46

Disadvantages of Structured Programming
Approach:
⚫ Since it is Machine-Independent, So it takes time to convert
into machine code.
⚫ The converted machine code is not the same as for assembly
language.
⚫ The program depends upon changeable factors like data-
types. Therefore it needs to be updated with the need on the go.
⚫ Usually the development in this approach takes longer time as
it is language-dependent. Whereas in the case of assembly
language, the development takes lesser time as it is fixed for the
machine.
47

1.8. Program Design
The next stage is the program design. The
software developer makes use of tools like algorithms
and flowcharts to develop the design of the program.
⚫Algorithm
⚫Flowchart
48 3/29/22

1.8. Program Design
1. Definition of Algorithm
⚫ To write a logical step-by-step method to solve the problem is
called the algorithm; in other words, an algorithm is a
procedure for solving problems. In order to solve a
mathematical or computer problem, this is the first step in
the process. An algorithm includes calculations, reasoning,
and data processing. Algorithms can be presented by natural
languages, pseudocode, and flowcharts, etc.
2. Definition of Flowchart
⚫ A flowchart is the graphical or pictorial representation of an
algorithm with the help of different symbols, shapes, and
arrows to demonstrate a process or a program. With
algorithms, we can easily understand a program. The main
purpose of using a flowchart is to analyze different methods.
Several standard symbols are applied in a flowchart:
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1.8. Program Design
Definition of Flowchart
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Start and stop
Flow or connection
Input or output
process
condition

1.8. Program Design
Example 1: Convert Temperature from Fahrenheit (0F) to Celsius (0C)
Flowchart:
Algorithm:
⚫ Step 1: Start
⚫ Step 2: Read temperature in Fahrenheit,
⚫ Step 3: Calculate temperature with formula C=5/9*(F-32),
⚫ Step 4: Print C
⚫ Step 5 : End
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1.8. Program Design
Example 2: Determine Whether A Student Passed the Exam or Not:
52 3/29/22
formula
Algorithm:
⚫ Step 1: Start
⚫ Step 2: Input grades of 4 courses M1, M2, M3 and M4,
⚫ Step 3: Calculate the average grade
with "Grade=(M1+M2+M3+M4)/4"
⚫ Step 4: If the average grade is less than 60, print "FAIL", else print
"PASS".
⚫ Step 5: End

Con….
Flowchart:
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1.8. Program Design
Example 3: Print 1 to 20 Flowchart:
Algorithm:
⚫ Step 1: Start
⚫ Step 2: Initialize X as 0,
⚫ Step 3: Increment X by 1,
⚫ Step 4: Print X,
⚫ Step 5: If X is less than 20 then go back to step 2.
⚫ Step 6: End
54 3/29/22

1.8. Program Design
Example 4: Calculate the Interest of a Bank Deposit
Flowchart:
Algorithm:
⚫ Start 1: Start
⚫ Step 2: Read amount,
⚫ Step 3: Read years,
⚫ Step 4: Read rate,
⚫ Step 5: Calculate the interest with the formula
"Interest=Amount*Years*Rate/100
⚫ Step 6: Print interest,
⚫ Step 7: End
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1.8. Program Design
Example 5: Determine and Output Whether Number N is Even or Odd
Flowchart:
Algorithm:
⚫ Step 1: Start
⚫ Step 2: Read number N,
⚫ Step 3: Set remainder as N modulo 2,
⚫ Step 4: If the remainder is equal to 0 then number N
is even, else number N is odd,
⚫ Step 5: Print output.
⚫ Step 6: End
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1.8. Program Design
Example 6: Determine Whether a Temperature is Below or Above the
Freezing Point
Algorithm:
⚫ Step 1:Start
⚫ Step 2: Input temperature,
⚫ Step 3: If it is less than 32, then print "below freezing point",
otherwise print "above freezing point".
⚫ Step 4: End
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Flowchart:
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1.8. Program Design
Example 7: Determine Whether A Student Passed the Exam or Not:
Flowchart:
Algorithm:
⚫ Step 1:Start
⚫ Step 2: Input grades of 4 courses M1, M2, M3 and
M4,
⚫ Step 3: Calculate the average grade with the
formula "Grade=(M1+M2+M3+M4)/4"
⚫ Step 4: If the average grade is less than 60, print
"FAIL", else print "PASS".
⚫ Step 5: End
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1.8. Program Design(Pseudo Code)
Pseudo Code in C
⚫ Pseudo code in C is a simple way to write programming
code in English.
⚫ Pseudo-code is informal writing style for program
algorithm independent from programming languages to
show the basic concept behind the code.
⚫ Pseudocode is not an actual programming language. So it
cannot be compiled and not be converted into an
executable program.
⚫ It uses short or simple English language syntax to write
code for programs before it is converted into a specific
programming language.
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1.8. Program Design(Pseudo Code)
Pseudocode is also known as Program Design
Language (PDL) or Structured has the following characteristics:
⚫ A free syntax of natural language that describes a processing
feature.
⚫ A subprogram definition and calling techniques.
⚫ Fixedsyntax of keywords that provide for all
structured constructs, data declarations and modularity
characteristics.
⚫ A data declaration facility.
Pseudocode is a set of sequential written human
language instructions, usually numbered, that is used to
describe the actions a program will take when it is coded in a
programming language.
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62 3/29/22

1.9. Debugging
⚫ At this stage the errors in the programs are detected
and corrected.
⚫ This stage of program development is an important
process. Debugging is also known as program
validation.
⚫ Some common errors which might occur in the
programs include:
⚫Un initialization of variables.
⚫Reversing of order of operands.
⚫Confusion of numbers and characters.
⚫Inverting of conditions eg jumping on zero instead of on
not zero.
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Finished
Unit 1
64 3/29/22

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