A decision inside a decision

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Quick Questions

Shade in the A or B circle for each question.

1. Which describes a nested IF?

A Two IFs written one after the other with nothing inside them

B A second IF written inside the THEN or ELSE path of the first IF

2. In this algorithm, when is the inner IF checked? IF score > 10 THEN IF score > 50 THEN say "Wow!" END IF END IF

A Only when score > 10 is true

B Every time, even when score is 3

3. Which nested IF is laid out correctly?

A The inner IF is indented, and each IF has its own END IF

B The inner IF is not indented, and one END IF closes both IFs

4. A game has two IFs, one inside the other. How many END IF lines does it need?

A 2 END IF lines, one for each IF

B 1 END IF line, because the IFs are joined

5. Game level example: IF level = 1 THEN IF lives = 0 THEN say "Game over" END IF END IF If level is 2, what happens to the inner IF?

A It is checked and says Game over

B It is skipped and never checked

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1IF score > 50 THEN IF lives > 0 THEN SAY "Next level" END IF END IF		AThe inner IF is not indented, so it is hard to see that it is inside the first IF's THEN path.
2 IF lives > 0 THEN		BIF level = 1 THEN SAY "Easy mode" ELSE IF level = 2 THEN SAY "Medium mode" END IF END IF
3Each IF needs its own END IF, so two IFs need two END IFs.		CIF coins = 10 THEN IF key = 1 THEN SAY "Door opens" END IF END IF
4An IF inside the ELSE path is only checked when the first condition is false.		DA nested IF: the inner IF about lives is only checked when the score is over 50.
5IF score > 50 THEN IF lives > 0 THEN SAY "Next level" END IF		EThe outer IF has no END IF. Each IF needs its own END IF, so this needs a second END IF at the end.
6IF score > 50 THEN IF lives > 0 THEN SAY "Next level" END IF END IF		FThe inner IF is indented to show it belongs inside the outer IF's path.

Definitions

nested IF

Fill in the Blanks

Complete each line of code by filling in the missing parts.

IF score >= 50 THEN __ lives > 0 THEN SAY "Go to level 2"

IF coins > 10 THEN IF key = "yes" ____ SAY "Door opens"

SAY "Door opens" ______ END IF

ELSE IF lives _ 0 THEN SAY "Try again"

IF level _ 3 THEN IF boss_beaten = "yes" THEN SAY "You win!"

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A IF lives > 0 THEN

B SET bonus TO 0

C IF score > 50 THEN

D SET bonus 10

E END IF

F END IF

Question 2

A IF key = 1 THEN

B IF door = open

C SAY You win

D END IF

E END IF

Question 3

A score >= 100 THEN

B IF lives > 0 THEN

C SET level TO 2

D END IF

E END IF

Question 4

A IF hasMap = YES THEN

B IF hasKey YES THEN

C SAY Open the chest

D END IF

E END IF

Question 5

A IF lives < 0 THEN

B IF score > 50 THEN

C SAY Bonus level

D END IF

E END IF

Answer Key

A decision inside a decision

Section A: Quick Questions

B — A second IF written inside the THEN or ELSE path of the first IF

A — Only when score > 10 is true

A — The inner IF is indented, and each IF has its own END IF

A — 2 END IF lines, one for each IF

B — It is skipped and never checked

Section B: Match the Pairs

IF score > 50 THEN IF lives > 0 THEN SAY "Next level" END IF END IF → A nested IF: the inner IF about lives is only checked when the score is over 50.

IF lives > 0 THEN → The inner IF is indented to show it belongs inside the outer IF's path.

Each IF needs its own END IF, so two IFs need two END IFs. → IF coins = 10 THEN IF key = 1 THEN SAY "Door opens" END IF END IF

An IF inside the ELSE path is only checked when the first condition is false. → IF level = 1 THEN SAY "Easy mode" ELSE IF level = 2 THEN SAY "Medium mode" END IF END IF

IF score > 50 THEN IF lives > 0 THEN SAY "Next level" END IF → The outer IF has no END IF. Each IF needs its own END IF, so this needs a second END IF at the end.

IF score > 50 THEN IF lives > 0 THEN SAY "Next level" END IF END IF → The inner IF is not indented, so it is hard to see that it is inside the first IF's THEN path.

Section C: Definitions

nested IF — A second IF written inside the THEN or ELSE path of the first IF. It is only checked when that path is taken. Indent it and give each IF its own END IF.

Section D: Fill in the Blanks

IF score >= 50 THEN
  IF lives > 0 THEN
    SAY "Go to level 2"

IF coins > 10 THEN
  IF key = "yes" THEN
    SAY "Door opens"

    SAY "Door opens"
  END IF
END IF

ELSE
  IF lives > 0 THEN
    SAY "Try again"

IF level = 3 THEN
  IF boss_beaten = "yes" THEN
    SAY "You win!"

Section E: Spot the Error

D — The step inside the inner IF is missing the word TO. It should be ' SET bonus TO 10'. This step only runs when both IFs are true.

B — The inner IF is missing THEN. Every IF needs THEN after its condition: ' IF door = open THEN'.

A — The outer decision must start with the word IF. It should be 'IF score >= 100 THEN'.

B — The inner condition is missing the = sign, so it does not compare anything. It should be ' IF hasKey = YES THEN'.

A — Lives are never below 0 while playing, so the THEN path is never taken and the inner IF is never checked. It should be 'IF lives > 0 THEN'.