Flowcharts and Introduction to computers

Introduction to computers
and Computing

Flow Charts
A schematic representation of sequence of
operations to achieve a task.
 Also called “Flow Diagram” or “Flow
Sheet”
This helps us to show the flow of program
graphically.

How to represent using Flow Chart?
There are certain symbols that are connected together
to form a complete Flow Chart for a particular problem
These symbols represent:
1. Start/End
2. Read/Print (Input/Output)
3. Arithmetic operations
4. Conditions
5. Connectors
6. Flow line
of the program

(Contd.)
 This sign represents a limitation.
 It shows where the program starts, and where it ends.
START END
The Oval.

(Contd.)
A PARALLELOGRAM
This sign represents an Input or an Output.
READ PRINT

(Contd.)
A RECTANGLE.
S = a + b
 This is where we want to show an arithmetic
function
(+,-,*,/,^), or to give a number or a string it's value.
NOTE: You must never write for example "a + b = s"

(Contd.)
A Square
condition
yes
No
 This represents a condition.
 Inside we write the condition, and if that condition is true,
then the flow branches to “YES” else to “NO”.
NOTE: This sign must always have two exits: "YES", if the
condition is fulfilled and "NO", if the condition is not
fulfilled.

(Contd.)
 These are the flow lines.
 They connect various blocks in a Flow Chart.

(Contd.)
 These are the connectors.
 They connects portion of algorithm and inside
use of start and end symbols.
Module

Flow Chart
Algorithms are more easily understood if they mainly
use self-contained modules and
1-Sequence logic or Sequential flow
2-Selection logic or Conditional flow
3-Iterative logic or Repetitive flow

Sequence logic (Sequential flow)
Sequence logic are executed in the obvious
sequence. The sequence may be presented
explicitly, by means of numbered steps, or
implicitly , by the order in which the module are
written.
Module A
Module B
Module C

Selection Logic (Conditional Flow)
Selection logic employs a number of conditions which lead
to a selection of one out of several alternative
modules. The structures which implement this logic are
called selection structures.
These selection structures fall into three types.
 Single selection ( If structure )
 Double selection ( If/else structure)
 Multiple selection ( if/else if / else or Switch
structure )

Single selection:
The logic of this structure is, If the
condition holds, then Module A , which
may consist of one or more statements is
executed ; otherwise Module A is skipped
and control transfers to the next step of
the algorithm.

Single Selection:
Condition ?
Module A
Yes
No

Double selection:
Condition ?
Module A Module B
No
Yes

PSEUDOCODE – Execution of if-
then-else
Multiple selection :
F
T
Break
T
Break
T
Break
F
.
.
.
F

Iterative Logic (Repetitive Flow)
The third kind of logic refers to either of two
types of structures involving loops. Each
type begins with a repeat statement and is
followed by a module ,called the body of
the loop.
1-While structure
2-For Structure

While Structure :
Condition ?
Module
(body of loop)
No
Yes

For Structure :
KR
Is K > S ?
Module
(body of loop)
KK+T
No
Yes

Example – Add two numbers, calculate &
print the sum.
A Flow Chart
Start
End
READ a, b
S := a + b
Print S

Impact of the computer language
 An algorithm is expressed in abstract terms.
 To be intelligible to a computer, it needs to be
expressed in a language understood by it.
 The only language really understood by a
computer is its own machine language.
 Programs expressed in the machine language
are said to be executable.
 A program written in any other language needs
to be first translated to the machine language
before it can be executed.

 A machine language is far too cryptic to be
suitable for the direct use of
programmers.
 A further abstraction of this language is
the assembly language which provides
mnemonic names for the instructions and
a more intelligible notation for the data.
 An assembly language program is
translated to machine language by a
translator called an assembler

 Even assembly languages are difficult to work
with.
 High-level languages such as C provide a much
more convenient notation for implementing
algorithms.
 They liberate programmers from having to think
in very low-level terms, and help them to focus
on the algorithm instead.
 A program written in a high-level language is
translated to assembly language by a translator
called a compiler.
 The assembly code produced by the compiler is
then assembled to produce an executable
program.

A Simple C Program
 #include <iostream.h>
 int main (void)
 {
 printf("Hello Worldn“);
 }

Annotation for the simple c program
 This line uses the preprocessor
directive #include to include the contents
of the header file iostream.h in the
program. Iostream.h is a standard C++
header file and contains definitions for
input and output.

Cont…
 This line defines a function called main.
 A function may have zero or more parameters;
these always appear after the function name,
between a pair of brackets.
 The word void appearing between the brackets
indicates that main has no parameters.
 A function may also have a return type; this
always appears before the function name.
 The return type for main is int (i.e., an integer
number).
 All C++ programs must have exactly one main
function. Program execution always begins from
main.

Cont…
 This brace marks the beginning of the body of
main.
 This line is a statement.
 A statement is a computation step which may
produce a value.
 The end of a statement is always marked with a
semicolon (;).
 This statement causes the string "Hello Worldn"
to be sent to the printf output stream.
 A string is any sequence of characters enclosed
in double-quotes.
 The last character in this string (n) is a newline
character which is similar to a carriage return on
a type writer.

 This brace marks the end of the body of
main.

Variable
 A variable is a symbolic name for a memory
location in which data can be stored and
subsequently recalled.
 Variables are used for holding data values so that
they can be utilized in various computations in a
program.
 All variables have two important attributes:
 A type which is established when the variable is
defined (e.g., integer, real, character). Once defined, the
type of a C variable cannot be changed.
 A value which can be changed by assigning a new
value to the variable. The kind of values a variable can
assume depends on its type. For example, an integer
variable can only take integer values (e.g., 2, 100, -12).

Flowcharts and Introduction to computers

More Related Content

Similar to Flowcharts and Introduction to computers (20)

Recently uploaded (20)

Flowcharts and Introduction to computers