briefly explain the various stages of problem solving class 11

Introduction to Problem Solving Class 11 Notes | CBSE Computer Science

Latest Problem Solving Class 11 Notes includes Problem Solving, steps, algorithm and its need, flow chart, pseudo code with lots of examples.

1 What is Problem Solving?
2 Steps for problem solving
3 What is Algorithm?
4 Why do we need Algorithm?
5.1 Flow chart
5.2 Flow Chart Examples
5.3 Pseudo code
5.4 Pseudo Code Example
6.1 Selection
6.2 Algorithm, Pseudocode, Flowchart with Selection ( Using if ) Examples
6.3 Repetition
6.4 Algorithm, Pseudocode, Flowchart with Repetition ( Loop ) Examples
7 Decomposition

What is Problem Solving?

Problem solving is the process of identifying a problem, analyze the problem, developing an algorithm for the identified problem and finally implementing the algorithm to develop program.

Steps for problem solving

There are 4 basic steps involved in problem solving

Analyze the problem

Developing an algorithm
Testing and debugging

Analyzing the problem is basically understanding a problem very clearly before finding its solution. Analyzing a problem involves

List the principal components of the problem
List the core functionality of the problem
Figure out inputs to be accepted and output to be produced

Developing an Algorithm

A set of precise and sequential steps written to solve a problem
The algorithm can be written in natural language
There can be more than one algorithm for a problem among which we can select the most suitable solution.

Algorithm written in natural language is not understood by computer and hence it has to be converted in machine language. And to do so program based on that algorithm is written using high level programming language for the computer to get the desired solution.

Testing and Debugging

After writing program it has to be tested on various parameters to ensure that program is producing correct output within expected time and meeting the user requirement.

There are many standard software testing methods used in IT industry such as

Component testing
Integration testing
System testing
Acceptance testing

What is Algorithm?

A set of precise, finite and sequential set of steps written to solve a problem and get the desired output.
Algorithm has definite beginning and definite end.
It lead to desired result in finite amount of time of followed correctly.

Why do we need Algorithm?

Algorithm helps programmer to visualize the instructions to be written clearly.
Algorithm enhances the reliability, accuracy and efficiency of obtaining solution.
Algorithm is the easiest way to describe problem without going into too much details.
Algorithm lets programmer understand flow of problem concisely.

Characteristics of a good algorithm

Precision — the steps are precisely stated or defined.
Uniqueness — results of each step are uniquely defined and only depend on the input and the result of the preceding steps.
Finiteness — the algorithm always stops after a finite number of steps.
Input — the algorithm receives some input.
Output — the algorithm produces some output.

What are the points that should be clearly identified while writing Algorithm?

The input to be taken from the user
Processing or computation to be performed to get the desired result
The output desired by the user

Representation of Algorithm

An algorithm can be represented in two ways:

Pseudo code

Flow chart is visual representation of an algorithm.
It’s a diagram made up of boxes, diamonds and other shapes, connected by arrows.
Each step represents a step of solution process.
Arrows in the follow chart represents the flow and link among the steps.

briefly explain the various stages of problem solving class 11

Flow Chart Examples

Example 1: Write an algorithm to divide a number by another and display the quotient.

Input: Two Numbers to be divided Process: Divide number1 by number2 to get the quotient Output: Quotient of division

Step 1: Input a two numbers and store them in num1 and num2 Step 2: Compute num1/num2 and store its quotient in num3 Step 3: Print num3

Pseudo code means ‘not real code’.
A pseudo code is another way to represent an algorithm. It is an informal language used by programmer to write algorithms.
It does not require strict syntax and technological support.
It is a detailed description of what algorithm would do.
It is intended for human reading and cannot be executed directly by computer.
There is no specific standard for writing a pseudo code exists.

Keywords used in writing pseudo code

Pseudo Code Example

Example: write an algorithm to display the square of a given number.

Input, Process and Output Identification

Input: Number whose square is required Process: Multiply the number by itself to get its square Output: Square of the number

Step 1: Input a number and store it to num. Step 2: Compute num * num and store it in square. Step 3: Print square.

INPUT num COMPUTE square = num*num PRINT square

Example: Write an algorithm to calculate area and perimeter of a rectangle, using both pseudo code and flowchart.

INPUT L INPUT B COMPUTER Area = L * B PRINT Area COMPUTE Perimeter = 2 * ( L + B ) PRINT Perimeter

Flow of Control

An algorithm is considered as finite set of steps that are executed in a sequence. But sometimes the algorithm may require executing some steps conditionally or repeatedly. In such situations algorithm can be written using

Selection in algorithm refers to Conditionals which means performing operations (sequence of steps) depending on True or False value of given conditions. Conditionals are written in the algorithm as follows:

If <condition> then Steps to be taken when condition is true Otherwise Steps to be taken when condition is false

Algorithm, Pseudocode, Flowchart with Selection ( Using if ) Examples

Example: write an algorithm, pseudocode and flowchart to display larger between two numbers

INPUT: Two numbers to be compared PROCESS: compare two numbers and depending upon True and False value of comparison display result OUTPUT: display larger no

STEP1: read two numbers in num1, num2 STEP 2: if num1 > num2 then STEP 3: display num1 STEP 4: else STEP 5: display num2

INPUT num1 , num2 IF num1 > num2 THEN PRINT “num1 is largest” ELSE PRINT “num2 is largest” ENDIF

Example: write pseudocode and flowchart to display largest among three numbers

INPUT: Three numbers to be compared PROCESS: compare three numbers and depending upon True and False value of comparison display result OUTPUT: display largest number

INPUT num1, num2, num3 PRINT “Enter three numbers” IF num1 > num2 THEN IF num1 > num3 THEN PRINT “num1 is largest” ELSE PRINT “num3 is largest” END IF ELSE IF num2 > num3 THEN PRINT “num2 is largest” ELSE PRINT “num3 is largest” END IF END IF

Repetition in algorithm refers to performing operations (Set of steps) repeatedly for a given number of times (till the given condition is true).
Repetition is also known as Iteration or Loop

Repetitions are written in algorithm is as follows:

While <condition>, repeat step numbers Steps to be taken when condition is true End while

Algorithm, Pseudocode, Flowchart with Repetition ( Loop ) Examples

Example: write an algorithm, pseudocode and flow chart to display “Techtipnow” 10 times

Step1: Set count = 0 Step2: while count is less than 10, repeat step 3,4 Step 3: print “techtipnow” Step 4: count = count + 1 Step 5: End while

SET count = 0 WHILE count<10 PRINT “Techtipnow” Count = count + 1 END WHILE

Example: Write pseudocode and flow chart to calculate total of 10 numbers

Step 1: SET count = 0, total = 0 Step 2: WHILE count < 10, REPEAT steps 3 to 5 Step 3: INPUT a number in var Step 4: COMPUTE total = total + var Step 5: count = count + 1 Step 6: END WHILE Step 7: PRINT total

Example: Write pseudo code and flow chart to find factorial of a given number

Step 1: SET fact = 1 Step 2: INPUT a number in num Step 3: WHILE num >=1 REPEAT step 4, 5 Step 4: fact = fact * num Step 5: num = num – 1 Step 6: END WHILE Step 7: PRINT fact

Decomposition

Decomposition means breaking down a complex problem into smaller sub problems to solve them conveniently and easily.
Breaking down complex problem into sub problem also means analyzing each sub problem in detail.
Decomposition also helps in reducing time and effort as different subprograms can be assigned to different experts in solving such problems.
To get the complete solution, it is necessary to integrate the solution of all the sub problems once done.

Following image depicts the decomposition of a problem

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