1. Introduction to Algorithms and Programming
Dr. Majed Bouchahma

2. What is an Algorithm ?
An algorithm is a sequence of finite instructions, often used for calculation and data processing.
It is formally a type of effective method in which a list of well-defined instructions for completing a task will, when given an initial state, proceed through a well-defined series of successive states, eventually terminating in an end-state.

3. What is an Algorithm ?
There are two commonly used tools to help to document program logic (the algorithm). These are flowcharts and Pseudocode. We will use both methods here. Generally, flowcharts work well for small problems but Pseudocode is used for larger problems.

4. What is an Algorithm ? Algorithms must:
1. Be well-ordered and unambiguous
2. Be executable (understandable),
3. Solve the problem, and
4. Terminate.

5. Example: Write an algorithm to add two numbers
Start
Step 1: Get number1
Step 2: Get number2
Step 3: Sum --- number1 + numbert2
Step 4: Display/Print sum
Stop

6. Basic (primitive) operations involved
Read the input from user
Carry out basic arithmetical computations
Print the output to the user

7. The key features of an algorithm
Sequence (also known as Process)
Decision (also known as Selection)
Repetition (also known as Iteration or Looping)

8. Write and algorithm to compare two numbers and print the smallest number
Start:
Step 1: Get number1
Step 2: Get number2
Step 3: If number1< number2
Step 4: print number1 is smaller
Step 4: else print number2 is smaller.
Stop

9. Pseudocode Pseudocode is a more simplified version of an algorithm.
An algorithm may be written using a certain language like C but seudocode is always written in simple English statements.

10. Pseudocode
Allows the designer to focus on the logic of the algorithm without being distracted by details of language syntax.

11. The problem:
Design a program which accepts as input two numbers and calculates sum and difference and then displays both the sum and the difference.

12. Psuedocode: Start Step1: Read the first number
Step2: Read Second Number
Step3: Add the numbers together
Step4: Find the difference between the numbers
Step5: Display the sum
Step6: Display the difference
Stop

13. Variables A named location that stores a value
C = A + B
B = 4
A = 7
A = A + 3
A = A + C A B C

14. Conditionals Statement implemented if condition is true
A=1, B=2, C=3, D=4
if A < B
C = 5
if A > B
D = 4
if C < D
B = B + 1
else
B = B - 1 A B C D 1 2 3 4

15. Algorithm: Start Step1: Read Number1 Step2: Read Number2
Step3: Sum = Number1 + Number2
Step4: Difference = Number1 - Number2
Step5: DISPLAY Sum
Step6: DISPLAY Difference
Stop

16. Arithmetic operators
  +         add
    -         subtract
    *        multiply
   /      divide
    =       assign

17. Relational operators. == equal to (a pair of equals signs)
<= less than or equal to
>= greater than or equal to
<> not equal to

18. Logical operators
AND OR
NOT

19. IF (x = = 32) AND (y = = 7) THEN
sumxy = x + y

20. IF (letter = = 'A') OR (letter = = 'E') THEN DISPLAY 'Vowel‘
IF NOT (letter = =  'A') THEN
DISPLAY 'Not letter A'

21. Order of precedence for operators
( ) parentheses
NOT
* / AND
+  -  OR
==  >  <  <>  >=  <=
from left to right.

22. Flowcharts
Definition: Flow chart is a graphical method of to represent the algorithm that is a popular tool to design programs.
- Following symbols are used to draw a flow chart

23. Draw a flow chart that accepts two numbers and displays the sum.
Draw a flowchart for the problem that is accepting two numbers and calculating sum and difference and then displaying the result

24. A flowchart that reads the name of the students in the class and displays it.
Start
Display the name of the student
Is there any more student in the class?
Stop
Read the name of the student
yes no

25. Draw a flowchart to add all the numbers from 1 to 20.
Start
Display Sum
Number =1
Is Number=20
Sum=Sum+Number
Sum =0
Number =Number+1
Stop

26. Psuedocode Step 1: Set Number=1 Step 2: Set Sum=0
Step 3: Sum=Sum+Number
Step 4: Check if Number =20
Step 5: if yes Display the Sum
Step 6: Stop
Step 7: Otherwise Number=Number+1
Step 8: Go to step 3

28. A program has to be written to display the grades of the students in a class of 30 students. Grade is calculated on the basis of percentage (%) marks obtained by the student.
More than or equal to 80% A
More than or equal to 60% B
More than or equal to 50% C
More than or equal to 40% D
Less than 40% F (Fail)
Draw a flowchart and write the corresponding algorithm.

29. Get the mark of the Student Are there more students?
Start
Mark>=80?
Get the mark of the Student
Mark>=60?
Mark>=50?
Mark>=40?
Are there more students?
Display Grade A
Display Grade D
Display Grade B
Display Grade C
Display Grade F
Stop
yes
yes
yes
yes

30. Draw a flowchart that accepts 3 numbers say x, y, and z from the user and finds the largest number. Note that your flowchart should use minimum number of decision boxes.

31. Start Is x > y Display z is largest Is y > z Is x > z
Display x is largest
Display y is largest
Get x, y, z
Stop
yes
yes no no no
yes

32. Some rules for flow charts
Every flow chart has a START symbol and a STOP symbol
The flow of sequence is generally from the top of the page to the bottom of the page. This can vary with loops, which need to flow back to an entry point.
Use arrowheads on connectors where flow direction may not be obvious.
There is only one flow chart per page
A page should have a page number and a title
A flow chart on one page should not break and jump to another page
A flow chart should have no more than around 15 symbols (not including START and STOP)