Computer Applications: Secondary Level: Unit-4: 4.5. Program Control Structures, Explanations, Administrators

4.5. Program Control Structures

The designs which direct the request in which program articulations are executed are called Control Structures. There are 3 kinds of control structure. They are:


It is the arrangement of program guidelines which keep each other and are to be executed genuinely (not subject to any program conditions). Guidelines are placed in a predefined succession (very much like a line in a film lobby) and the following guidance is executed by CPU solely after the execution of the past guidance (C never precedes B).


It is the arrangement of directions which are to be executed restrictively for example they are executed in light of a condition that can be either obvious or misleading. Usually involved rationale for choice are if condition, if else condition, if else if condition, settled if else condition and switch case condition.

If condition

On the off chance that condition is utilized in the event that the given issue has just a single condition and just a single activity. Taking into account either obvious or misleading part, in the event that the given condition is valid, the articulation will be executed. In any case, the control exits from the condition.

else If condition

This condition is utilized on the off chance that the issue has one condition however two elective activities. Here, assuming the condition is valid, explanation 1 will be executed; if not, articulation 2 will be executed.


These are the PC guidelines which are to be performed more than once and restrictively for example circle articulations are driven by the circle condition. Generally involved rationale for emphasis are while circle, do while circle and for a circle.

While circle

In this circle, first, the condition is really taken a look at by the PC and in the event that the condition ends up being valid, the explanation inside the circle is executed. This cycle is rehashed and the worth of augmentation and decrement administrator is continuously evolving. At the point when the condition is bogus, the circle stops.

Calculation Syntax

Introduction while (condition) { proclamations … … … … … … . … … … … … … . increase/decrement }

Do while circle

In this circle, first, the PC really looks at the underlying worth; second executes the assertions inside the circle lastly, actually takes a look at the condition. The cycle is rehashed for next pass, in the event that the condition is valid. In any case, the circle stops. Assuming the condition is at first bogus, it will execute for somewhere around one time.

Calculation Syntax

Introduction do { proclamations … … … … … … .. … … … … … … .. increase/decrement

} while (condition)

For circle

It is the most normally utilized circle. It comprises of 3 articulations; instatement, condition and counter, which are characterized inside an explanation.

Calculation Syntax

for (introduction; condition; counter) { articulations … … … … … … . … … … … … … . }

Where, introduction is beginning stage, the condition is place to pause and augmentation/decrement is a counter.

4.6. Program Design Tools

Otherwise called the Programming instruments, Program Design apparatuses are the instruments used to foster a program. During planning a program, various devices are expected to take care of a few issues. A portion of the regularly utilized instruments are:

1. Calculation

A calculation is a grouping of guidelines or bit by bit guidance to track down the arrangement of an issue. A calculation ought to be basic and clear. It should be direct and ought to prompt the arrangement of the issue in a limited number of steps. A calculation is an assortment of a limited number of directions organized in a grouping to track down the arrangement of an issue.

Model 1: Algorithm for adding the two numbers.

Stage 1: Start the program
Stage 2: Input number x, y
Stage 3: Read x, y
Stage 4: Z = x + y
Stage 5: Print Z
Stage 6: Stop the program

Model 2: A calculation to go to the film and see a film.

Stage 1: Start the program
Stage 2: Go to the film lobby
Stage 3: Is the ticket counter open ?
Stage 4: If it isn't open, get back Step 5: If it is open, purchase a ticket
Stage 6: Get into the film corridor
Stage 7: Watch the film
Stage 8: Return home
Stage 9: End the program

2. Flowchart

A flowchart is a pictorial portrayal of a calculation. We can likewise characterize it as a program arranging device for coordinating a grouping of steps important to tackle an issue, which is displayed with regards to images. Flowchart utilizes images that have mathematical shapes to show the various activities. These images are associated by stream lines which show the request for execution of the different exercises. It is utilized by the software engineers to foster projects and by framework, creators to address the general framework while examining and fostering the framework.


The upsides of flowchart are :

  • It is a free language. In this way, the flowchart we plan for programming in one language is material for programming in another dialect.
  • When the flowchart is ready, doing the coding by taking a gander at the algorithm is extremely simple.
  • Understanding the rationale of program by planning the flowchart is exceptionally simple. Indeed, even individuals who don't have the foggiest idea about the coding can figure out the rationale of a program with the assistance of flowchart.
  • Precise troubleshooting and testing is effectively conceivable with the assistance of flowchart.

The Disadvantages Of Flowchart Are

  • Setting up a flowchart is a tedious interaction.
  • In the event that there is an adjustment of rationale once more, we need to foster the new flowchart.
  • Flowchart gives no advantageous means to feature the main activity.
  • The flowchart is very expensive to create and challenging to utilize and make due.
  • Mind boggling and itemized graphs can be relentless to plan and draw.

Images for flowcharts:

3. Organized English (Pseudo code)

The general significance of Pseudo code is bogus code or phony code. Before we compose a genuine program, we compose a program that seems to be a code based on calculation and flowchart, which may not be linguistically right yet seems to be a program code is called Pseudo code. The guidance of pseudo code is composed by utilizing English expression and numerical articulation. It has no hard or quick principles for composing guidance yet the guidance is nearer to significant level language guidelines. Thusly, the pseudo code fashioners ought to have essential information about undeniable level language prior to composing it. It is free of any programming language.

Model: Pseudo code for ascertaining area of square shape
Input length, expansiveness
Ascertain area= length*breadth
Yield region

4.7. Prologue to QBASIC

Q-BASIC is a general programming language created by Microsoft Corporation, USA for microcomputers in 1985. It involves Interpreter as a language interpreter program. It utilizes a bunch of watchwords and numerical images to compose programs. The projects written in QBASIC should be changed over into machine codes by utilizing Interpreter.

4.7.1. Components of QBASIC

The components utilized in Q fundamental are as per the following:

  •  Character set
  •  Factors
  •  Constants
  •  Administrator and Operands
  •  Articulation
  •  Proclamations

Character Set

QBASIC has the person set comprising of the accompanying components:

1. Letters in order: A, B, C,....Z 2. Digits: 0, 1,
2........,9 and
3. Extraordinary characters: + - */( ) . , $ ; ,: ,= ,> ,< , ^

The image ^ (caret) is utilized to signify exponentiation administrator, the image * (indicator) is utilized to indicate augmentation and different images which have their typical implications.


An amount in a PC program which doesn't change its worth during the execution of the program is known as a steady. QBASIC permits the accompanying constants:

Numeric Constant

The numeric steady is one that is framed by a grouping of digits 0, 1, 2,.....9 and may incorporate a decimal point. A numeric consistent might be a number or a genuine number. 383, +57, 0, - 6.2 and 6.15E4 are legitimate numeric constants. The number 6.15E4, as a matter of fact, address 6.15 * 104. The documentation E is utilized to address the dramatic structure. The number after E is the type which can be positive or negative. Notwithstanding, its length can't surpass two digits.

String Constant

A string steady comprises of a grouping of characters which should be encased by a quote.


The amount which might change its qualities during the execution of the program is known as the variable.

In QBASIC, Variables Are Also Of Two Types

  • Numeric variable: Numeric variable can expect numeric worth and is addressed by a letter set or a letter set followed by another letters in order or digit. For instance A, C, A2, ABC, A6 and so on, address numeric factors.
  • String variable: A string variable is addressed by a letters in order followed by dollar ($) sign. It ought to be remembered that while building the string variable, dollar ($) ought to be the last person. For instance, B1$, NAME$, BOOK1$, and so on are substantial string factors.


An articulation can be a string, or numeric steady, a variable or a mix of constants, factors with administrators which return a solitary worth.


Operands are the information or factors on which numerical, intelligent and string activities happen.


Administrators are the images, which are utilized to perform explicit errand like number-crunching tasks, sensible articulations, and string articulations.


An assertion is a bunch of guidelines composed utilizing watchwords or orders of QBASIC. Each programming language involves watchwords as a proclamation with specific sentence structure.
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