Lecture 3 - Decision Structures and Boolean Logic

Question 1

What does sequential order describe?

Answer 1

Describes order in which statements are executed top to bottom (executed in the textual order they appear within the program)

Question 2

What is a selection statement?

Answer 2

Used to determine which of several actions to be taken given the value of some condition also known as selection structure or decision structure or conditionals.

Question 3

What is control structure?

Answer 3

logical design that determines the order in which a set of statements (or a set of statement sequences) will execute

Question 4

In python what does the ‘if’ statement determine?

Answer 4

whether or not the action associated with the statement(s) can be executed

Question 5

What is a single alternative decision structure?

Answer 5

Either the action is performed (when the condition is True) or it is not performed (when the condition is False).

Question 6

How is ‘if’ represented in a flowchart?

Answer 6

by a diamond

Question 7

What are boolean expressions?

Answer 7

Situations (i.e., conditions) examined by the if statement are themselves expressions that evaluate to true or false.
These expressions are called boolean expressions.
They often involve the use of one or more relational operators.

Question 8

What is a relational operator?

Answer 8

Determines whether or not a specific kind of ordering (i.e., a relation) exists between two operands

Question 9

What are some examples of relational operators?

Answer 9

< less than
> greater than
<= less than or equal to
>= greater than or equal to
== equals
!= doesn't equal (not equal)

Question 10

What is the syntax of the ‘if’ statement?

Answer 10

The first line includes the keyword ‘if’ this is followed by the boolean (i.e., True or False) expression, lastly there is an indented sequences of statements known as a block.
When the expression evaluates to True, all statements in the block are executed.
When the expression evaluates to False, no statement in the block is executed (i.e., all statements are skipped).

Question 11

What is the ‘if-else’ statement?

Answer 11

This enables two possible paths of execution and guarantees that exactly one of the paths will be taken.
One path is followed when the if-condition is True and the other path is followed when the if-condition is False.
The False path is indicated by the block following the else keyword.

Question 12

What is the simplest boolean operator?

Answer 12

‘not’
The simplest boolean operator as it takes a single boolean operand.
If its operand is True, the result is False.
If its operand is False, the result is True.

Question 13

What is the result of the boolean operator ‘and’ ?

Answer 13

Result is True only if both operands are True, and is False otherwise.

Question 14

How do we usually describe the results of boolean operators?

Answer 14

in the form of truth tables

Question 15

How many boolean operands does the operator ‘and’ need?

Answer 15

Takes two boolean operands

Question 16

How many boolean operands does the operator ‘or’ need?

Answer 16

Takes two boolean operands

Question 17

What is the result of the boolean operator ‘or’ ?

Answer 17

Result is True if either operand is True, and is False otherwise.

Question 18

What is the logical ‘and’ sometimes represented as?

Answer 18

Logical ‘and’ is sometimes called conjunction and in mathematics is represented by the ∧ symbol.

Question 19

What is the logical ‘or’ sometimes represented as?

Answer 19

Logical ‘or’ is sometimes called disjunction and in mathematics is represented by the ∨ symbol.

Question 20

What is a common use of boolean operators?

Answer 20

constructing range checks

e. g., Is some number within a range of low and high values?
e. g., Or is the value outside of that range?

Question 21

What are flags?

Answer 21

The results of boolean expressions may be assigned to variables. Such a variable then has a reference to True or False.
Sometimes such variables are very handy when creating flags.
Flags are used by other parts of the program to determine further action.

Question 22

What are the three main conditional statements?

Answer 22

‘if’, ‘if-else’ and ‘if-elif-else’.

Question 23

What can be used to express conditions for checking at execution time?

Answer 23

Relational operators and boolean operators