An algorithm is a precise set of unambiguous instructions that must be completed in a finite number of steps to solve a problem or reach a desired outcome. Key features of algorithms include being precise, unambiguous, terminating after a finite number of steps, avoiding infinite repetition of instructions, and obtaining the desired result upon termination. Examples provided calculate equality of two numbers, print the first 10 natural numbers, and find the sum of the first N natural numbers. Flow charts and pseudo code can be used to represent algorithms graphically or as informal high-level descriptions.

1. Idea of Algorithm

4. Features of an Algorithm
• Must be Precise.
• Must be Unambiguous.
• Should be completed in finite number of
steps.
• No instruction must be repeated infinitely.
• Each step must follow a specified order.
• After termination, desired result must be
obtained.

6. Example
• Test the equality of two numbers.
o Step 1: Start
o Step 2: Input first number as A
o Step 3: Input second number as B
o Step 4: if A=B
then print “Equal”
else
Print “Not Equal”
o Step 5: Stop

7. Example
• To print the first 10 natural numbers.
oStep 1: Start
oStep 2: [initialization] set i=1, n=10
oStep 3: Repeat step while i<=n
oStep 4: print i
oStep 5: Stop

8. Example
• To find sum of N natural numbers.
oStep 1: Start
oStep 2: Input N
oStep 3: [initialization] set i=1, sum=0
oStep 4: Repeat step while i<=N
oStep 5: set sum= sum+ i
Set i=i+1
oStep 4: print sum
oStep 5: Stop

9. Other Examples
1. Algorithm to find largest of three numbers.
2. To find whether a number is even or odd.
3. To find average of first N natural numbers.
4. To interchange / swapping of two variables.
Using/without using third variable.
5. To find area of a circle of radius r.
6. To find simple interest and compound interest for
principal p, rate r and time t.
7. To find roots of a quadratic equation.

11. Flow Chart
• Graphical representation of steps followed to
solve a given problem.
• Flow chart helps the viewers to visualize the
logic of the solution of a problem.
• In flow chart, each step is depicted by a
symbol and is associated with a short
description.

13. • Calculate the sum of first 10 natural numbers.
start
Set i=1 and Sum=0
Set sum=sum+i and i=i+1
Is i>10?
Display Sum
End
No
Yes

14. Pseudo Code
• It is a compact informal high-level description
of an algorithm that uses the structural
conventions of programming language.
• Pseudo codes are an outline of a program that
can easily be converted into programming
statements.

15. Keywords used while writing pseudo
codes:
1. IF (age>=18) then
display eligible to vote
ELSE
display not eligible
END IF

16. 2. WHILE (i<10)
print i
increment i by 1
END WHILE
3. FOR each student in the class
add 10 as bonus marks
END FOR