Once a decision point has been found, the next step is to state exactly what is tested there.
Definition
A logical condition is an expression that evaluates to either true or false. It is built from comparison operators and can be combined with the Boolean operators AND, OR and NOT.
Comparison and Boolean Operators
Key Point
| Operator | Meaning | Example that is true when age = 16 |
|---|---|---|
| == | Equal to | age == 16 |
| != | Not equal to | age != 18 |
| < and <= | Less than; less than or equal to | age <= 16 |
| > and >= | Greater than; greater than or equal to | age > 12 |
| AND | True only when both conditions are true | age >= 13 AND age <= 19 |
| OR | True when at least one condition is true | age < 5 OR age > 12 |
| NOT | Reverses the result | NOT (age == 18) |
Working Out the Condition for Each Decision
Worked Example
Worked Example: Cinema Tickets
A cinema sells a child ticket to anyone under 13 and a senior ticket to anyone aged 65 or over. Everyone else pays the standard price.
Testing the values on each side of a boundary shows whether a condition needs < or <=.
A cinema sells a child ticket to anyone under 13 and a senior ticket to anyone aged 65 or over. Everyone else pays the standard price.
pseudocode
if age < 13 then
ticket = "child"
elseif age >= 65 then
ticket = "senior"
else
ticket = "standard"
end if
| age | age < 13 | age >= 65 | ticket |
|---|---|---|---|
| 12 | True | Not tested | child |
| 13 | False | False | standard |
| 64 | False | False | standard |
| 65 | False | True | senior |
Exam Tip
State a condition exactly: "age is less than 13", not "the customer is young". Test the values on each side of every boundary, and check the order of the conditions, because once one condition is true the ones after it are not tested.