1. Introduction to Algorithms - 2
Dr. Khizar Hayat
Associate Prof. of Computer Science

2. What can a computer do
An algorithm can be written using six basic computer operations:
A computer can receive (input) information, e.g.
read name
get x
A computer can display (output) information, e.g.
write “the average is “, avg
display num
print “Hello!”
A computer can perform arithmetic operations, e.g.
set total total + numb
A computer can assign value to a variable, e.g.
set counter 0
set total  price+tax

3. What can a computer do
A computer can compare two pieces of information to select one of two actions, e.g.
if number < 0
then add 1 to neg_number
else add 1 to pos_number
end if
A computer can repeat a group of actions, e.g.
repeat untill total=50
read num
write num
set totaltotal+1
End repeat OR
while total ≤50
End while

4. Algorithm to add two numbers
begin
get num1
get num2
set sum  num1 + num2
display sum
end
Start
Read Num1
Read Num2
Sum Num1 + Num2
What about:
The difference of two numbers?
The sum and difference of two numbers?
Display Sum
Stop

5. Algorithm to input two numbers and print the smaller number
Start
begin
get num1
get num2
if num1 < num2
then display num1 as smaller
else display num2 as smaller
end if
end
Read Num1
Read Num2
Num1 < Num2? No
What about:
The largest of two numbers?
The largest of three numbers?
The median of three numbers?
Yes
Display
Num1 as min
Display
Num2 as min
Stop

6. Algorithm to sum five numbers input by the user
Start
count 0
begin
set count0
set sum0
repeat until count=5
get num
set countcount+1
set sumsum+num
end repeat
display sum as the total
end
sum 0
Read Num
count count + 1
sum sum + Num
count = 5? No
What about:
Sum of N numbers?
Average of N numbers?
Entering numbers till ‘-1’ is entered?
The sum of first 20 numbers?
Yes
Display
sum as total
Stop

7. Algorithm to compute the GCD of two numbers
begin
get numA
get numB
if numA > numB
then
set maqsnumA
set m_AlaihnumB
else
set maqsnumB
set m_alaihnumA
end if
set baqimaqs mod m_alaih
while baqi ≠ 0 do
set maqsm_alaih
set m_alaihbaqi
end while
display m_alaih as GCD
end
Display
M_Alaih as GCD
Stop
Maqs NumA
M_Alaih NumB
Start
Read NumA
Read NumB
NumA > NumB?
Yes No
Maqs NumB
M_Alaih NumA
Baqi = 0?
Maqs M_Alaih
M_Alaih baqi
Baqi Maqs mod M_Alaih
Euclid’s Algorithm

8. Exercises
Draw a flowchart that reads names of 50 students in the class and display it.
Page of notes
Page 21 of notes
Any sum in Omani currency?