4.5: Chained Decisions
- Page ID
- 117544
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- Identify the branches taken in an
if-elif
andif-elif-else
statement. - Create a chained decision statement to evaluate multiple conditions.
elif
Sometimes, a complicated decision is based on more than a single condition. Ex: A travel planning site reviews the layovers on an itinerary. If a layover is greater than 24 hours, the site should suggest accommodations. Else if the layover is less than one hour, the site should alert for a possible missed connection.
Two separate if
statements do not guarantee that only one branch is taken and might result in both branches being taken. Ex: The program below attempts to add a curve based on the input test score. If the input is 60
, both if
statements are incorrectly executed, and the resulting score is 75.
score = int(input())
if score < 70:
score += 10
# Wrong:
if 70 <= score < 85:
score += 5
Chaining decision statements with elif
allows the programmer to check for multiple conditions. An elif (short for else if) statement checks a condition when the prior decision statement's condition is false. An elif
statement is part of a chain and must follow an if
(or elif
) statement.
if-elif
statement template:
# Statements before
if condition:
# Body
elif condition:
# Body
# Statements after
elif
else
if-elif-else statements
Elifs can be chained with an if-else
statement to create a more complex decision statement. Ex: A program shows possible chess moves depending on the piece type. If the piece is a pawn, show moving forward one (or two) places. Else if the piece is a bishop, show diagonal moves. Else if . . . (finish for the rest of the pieces).
Lunchtime
Good afternoon
Too late
Write a program that reads in a crochet hook's US size and computes the metric diameter in millimeters. (A subset of sizes is used.) If the input does not match B-G, the diameter should be assigned with -1.0. Ex: If the input is D
, the output is "3.25 mm"
.
Size conversions for US size: mm
- B : 2.25
- C : 2.75
- D : 3.25
- E : 3.5
- F : 3.75
- G : 4.0
Write a program that reads in an integer representing a visible light wavelength in nanometers. Print the corresponding color using the following inclusive ranges:
- Violet: 380–449
- Blue: 450–484
- Cyan: 485–499
- Green: 500–564
- Yellow: 565–589
- Orange: 590–624
- Red: 625–750
Assume the input is within the visible light spectrum, 380-750 inclusive.
Given input:
550
The output is:
Green