Define conditional execution .

Conditional execution is a form of selection where a section of code runs only if a specified condition is true .

What happens when the condition of an IF statement is false?

The block is skipped and control passes to the next statement after the IF block .

Why do programs need selection ?

Programs need selection so they can respond differently to different situations ; without it, a program follows the same path regardless of input .

An IF statement evaluates a _______ condition and executes its block only if that condition is true.

An IF statement evaluates a Boolean condition and executes its block only if that condition is true.

What is displayed when this code segment runs? temp ← 20 IF(temp > 25) { DISPLAY("Hot") }

Nothing is displayed , because 20 > 25 is false , so the IF block is skipped.

How many branches of an IF-ELSE statement execute?

Exactly one branch of an IF-ELSE statement executes.

When should IF-ELSE be used instead of IF ?

IF-ELSE is used when a different action is needed for both the true and false cases .

Define nested conditional .

A nested conditional is an IF or IF-ELSE statement placed inside another IF or IF-ELSE block .

True or False? In a nested conditional, the inner condition is always evaluated.

False. The inner condition is only evaluated if execution reaches the branch that contains it .

What is displayed when this code segment runs? score ← 49 IF(score ≥ 50) { DISPLAY("Pass") } ELSE { DISPLAY("Fail") }

The code segment displays "Fail" , because 49 ≥ 50 is false, so the ELSE branch executes.

Iteration is a repeating portion of an algorithm .

Name the two iteration statements listed under Iteration on the AP Exam Reference Sheet.

The two iteration statements are REPEAT n TIMES and REPEAT UNTIL .

When should a REPEAT n TIMES loop be used?

REPEAT n TIMES is used when the number of repetitions is known in advance .

When should a REPEAT UNTIL loop be used?

REPEAT UNTIL is used when the number of repetitions depends on a changing value or user input .

How many times does the body of a REPEAT n TIMES loop run?

The body of a REPEAT n TIMES loop runs exactly n times .

True or False? The body of a REPEAT UNTIL loop always runs at least once.

False. If the condition is already true when the loop starts, the body does not execute at all .

What is displayed when this code segment runs? t ← 0 REPEAT 4 TIMES { t ← t + 5 } DISPLAY(t)

The code segment displays 20 , because 5 is added to t 4 times .

What is displayed when this code segment runs? k ← 10 REPEAT UNTIL(k < 4) { DISPLAY(k) k ← k - 3 }

The code segment displays 10 7 4 ; k then becomes 1, so k < 4 is true and the loop stops.

When does a REPEAT UNTIL loop terminate?

A REPEAT UNTIL loop terminates when its condition evaluates to true .

Define infinite loop .

An infinite loop occurs when the condition of a REPEAT UNTIL loop never becomes true , so the loop runs indefinitely .

Name two common causes of an infinite loop .

Common causes are the condition variable never being updated inside the loop body and a condition that is logically impossible to satisfy .

Every loop must have a clear, _________ stopping condition.

Every loop must have a clear, reachable stopping condition.

Will this loop ever stop? x ← 5 REPEAT UNTIL(x = 0) { x ← x + 2 }

This loop never stops : x increases by 2 each iteration, so it never equals 0 and the loop is infinite .

AP®Computer ScienceCollege BoardComputer Science PrinciplesFlashcardsUnit 3: Algorithms and ProgrammingControl Structures

Control Structures (College Board AP® Computer Science Principles): Flashcards

1/24

0Still learning

Know0

FrontConditionals
Define conditional execution.

Was this flashcard helpful?

Cards in this collection (24)

Define conditional execution.
Conditional execution is a form of selection where a section of code runs only if a specified condition is true.
What happens when the condition of an IF statement is false?
The block is skipped and control passes to the next statement after the IF block.
Why do programs need selection?
Programs need selection so they can respond differently to different situations; without it, a program follows the same path regardless of input.
An IF statement evaluates a _______ condition and executes its block only if that condition is true.
An IF statement evaluates a Boolean condition and executes its block only if that condition is true.
What is displayed when this code segment runs?
```
temp ← 20
```
```
IF(temp > 25)
```
```
{
```
```
   DISPLAY("Hot")
```
```
}
```
Nothing is displayed, because 20 > 25 is false, so the IF block is skipped.
How many branches of an IF-ELSE statement execute?
Exactly one branch of an IF-ELSE statement executes.
When should IF-ELSE be used instead of IF?
IF-ELSE is used when a different action is needed for both the true and false cases.
Define nested conditional.
A nested conditional is an IF or IF-ELSE statement placed inside another IF or IF-ELSE block.
True or False?
In a nested conditional, the inner condition is always evaluated.
False.
The inner condition is only evaluated if execution reaches the branch that contains it.
What is displayed when this code segment runs?
```
score ← 49
```
```
IF(score ≥ 50)
```
```
{
```
```
   DISPLAY("Pass")
```
```
}
```
```
ELSE
```
```
{
```
```
   DISPLAY("Fail")
```
```
}
```
The code segment displays "Fail", because 49 ≥ 50 is false, so the ELSE branch executes.

What is displayed when this code segment runs?

n ← 7

IF(n MOD 2 = 0)

   DISPLAY("Even")

ELSE

   IF(n > 5)

      DISPLAY("Big odd")

   ELSE

      DISPLAY("Small odd")

The code segment displays "Big odd": 7 MOD 2 is 1, so the outer ELSE runs, and 7 > 5 is true.

Define iteration.
Iteration is a repeating portion of an algorithm.
Name the two iteration statements listed under Iteration on the AP Exam Reference Sheet.
The two iteration statements are REPEAT n TIMES and REPEAT UNTIL.
When should a REPEAT n TIMES loop be used?
REPEAT n TIMES is used when the number of repetitions is known in advance.
When should a REPEAT UNTIL loop be used?
REPEAT UNTIL is used when the number of repetitions depends on a changing value or user input.
How many times does the body of a REPEAT n TIMES loop run?
The body of a REPEAT n TIMES loop runs exactly n times.
True or False?
The body of a REPEAT UNTIL loop always runs at least once.
False.
If the condition is already true when the loop starts, the body does not execute at all.
What is displayed when this code segment runs?
```
t ← 0
```
```
REPEAT 4 TIMES
```
```
{
```
```
   t ← t + 5
```
```
}
```
```
DISPLAY(t)
```
The code segment displays 20, because 5 is added to t 4 times.
What is displayed when this code segment runs?
```
k ← 10
```
```
REPEAT UNTIL(k < 4)
```
```
{
```
```
   DISPLAY(k)
```
```
   k ← k - 3
```
```
}
```
The code segment displays 10 7 4; k then becomes 1, so k < 4 is true and the loop stops.
When does a REPEAT UNTIL loop terminate?
A REPEAT UNTIL loop terminates when its condition evaluates to true.
Define infinite loop.
An infinite loop occurs when the condition of a REPEAT UNTIL loop never becomes true, so the loop runs indefinitely.
Name two common causes of an infinite loop.
Common causes are the condition variable never being updated inside the loop body and a condition that is logically impossible to satisfy.
Every loop must have a clear, _________ stopping condition.
Every loop must have a clear, reachable stopping condition.
Will this loop ever stop?
```
x ← 5
```
```
REPEAT UNTIL(x = 0)
```
```
{
```
```
   x ← x + 2
```
```
}
```
This loop never stops: x increases by 2 each iteration, so it never equals 0 and the loop is infinite.

Sign up to unlock flashcards

By signing up you agree to our Terms and Privacy Policy

Previous:Boolean ExpressionsNext:Developing Algorithms