1. Dry Run
You can test your program without using a computer by dry running it on paper
You act as the computer – following the instructions of the program, recording the valves of the variables at each stage
You can do this with a table

2. Dry Run
The table with have column headed with the names of the variables in the program
Each row in the table will be labelled with a line number form the program.
The entries of each row in th e table will be values of the variables after the execution of the statement on that line
You don’t need a row for every line in the program, just those lines where some significant change to the state of the program occurs e.g a variable gets a new value

3. Dry Run
In this table you can record all relevant changes to the variables as the program progresses, thereby test the logic of the program / algorithm
Do a dry run before you code your program on computer this way any logic errors will come to light during the dry run

4. Example of a Dry run L1 Declare two variables , first num second num
L2 Initialise both variables to 0
L3 first num = 0 second num = 0
L4 Ask user to enter first number
L5 Assign user input to first num variable
L6 Ask user to enter second number
L7 Assign user input to second num variable
L8 Add first num to second num
L9 Print result
Do a Dry run for this program assuming the user enters 17 for first number and 24 for the second

5. A sample Dry Run table After execution First num Second num Result
Line 2
Line 5 17
Line 7 24
Line 8 41

6. Relational Operators Give examples < less than > greater than
<= Less than or equal to a<=b
>= greater than or equal c>=d
== equals
!= not equals 5!=6
Boolean expression – TRUE or FALSE

7. If then Else statements
If <TEST>
<STATEMENT 1 >
Else
<STATEMENT 2 >
<TEST> is a boolean expression
Is <TEST? Has a false valve then <STATEMENT 2 > is executed
Is <TEST? Has a false valve then <STATEMENT 1 > is executed
Note the indentation – this makes it easier to read

8. Nesting Layout
To make your algorithm easier to read nest the statements
If (mark > 69)
grade = “A”
Else If (mark > 59)
grade = “B”
Else If (mark > 49)
grade = “C”
Else If (mark > 39)
grade = “D”
Else
grade = ‘F’
If (mark > 69)
grade = “A”
Else
If (mark > 59)
grade = “B”
If (mark > 49)
grade = “C”
If (mark > 39)
grade = “D”
grade = ‘F’
In this alternative the psuedo
code crawls across

9. Nesting of if-else and while loops
Int number
Number =3
For loop : 1 to 3
if number = 1
print ‘red’
else
if number = 2
print ‘green’
if number = 3
print ‘yellow’
endif
Loop end

10. More Complex Loop Tests
Sometimes we may want to allow the user to terminate the program/loop
We can do this by prompting the user with a question e.g imagine a user is entering a series of numbers which will be added to together, like student marks. We can ask the user the question (Do you want to add another student mark? )
We assign the user response to a variable named e.g. continue
Declare variable continue
Initialise the variable Continue = ‘X’
Ask the user (Do you want to add another student mark? )
Assign/store the user response to variable continue
Continue := user response
While (continue = ‘Y’)
Loop Body…

11. More Complex Loop Tests
Sometimes you may want to include more than one condition in your loop tests
In such cases you can use boolean connectives (&& and ||)
E.g.
while (continue = ‘y’) && (item number < 10)
Where item number = number of items to be added

12. Problem solving Understanding the problem
The plan – decide how to tackle problem - algorithms
Test and Evaluate – dry run and test plans

13. Test Plans Do before you code!
Do a test plan for every branch test e.g. if the else and loop statements
Extreme values such as 0 or negative numbers are tested in addition to ‘normal’ values. Testing the bounds is most efficient way for testing for run time errors

14. The following psuedo code / algorithm prints the larger of two numbers
Do a test plan to find it – a series of valves to be input in variables first and second .Run the program several times
Int first
Int second
Int max
Sring str
Prompt user to enter an integer (please enter a number)
Store the number into variable first
Prompt user to enter a second integer (please enter a second number)
Store the second number into variable second
Max = first
if (second > max)
max = second
Print message to screen saying (larger of the two numbers is max)

15. Test plan example Test number First Second Expected Result - max 1 1812 2 10 15 3 17 4 5 A 20
Error because not integer 6
-10
-17