Example: determining the quadrant

We can rewrite the nested quadrant example using a cascade:

x = int(input())
y = int(input())

if x > 0 and y > 0:
    print("First quadrant")
elif x > 0 and y < 0:
    print("Fourth quadrant")
elif y > 0:
    print("Second quadrant")
else:
    print("Third quadrant")

How it works

• Conditions are checked from top to bottom.
• The first true condition’s block runs, and the rest are skipped.
• If none are true, the else block runs (if present).
• You can have as many elif branches as needed, but only one if and at most one else.

When to use cascades instead of nesting

• When all conditions are mutually exclusive—only one can be true.
• To improve readability compared to deep nested ifs.
• When checking multiple possibilities of the same variable(s).

Example: grading system

score = int(input("Enter score: "))

if score >= 90:
    print("Grade: A")
elif score >= 80:
    print("Grade: B")
elif score >= 70:
    print("Grade: C")
elif score >= 60:
    print("Grade: D")
else:
    print("Grade: F")

Only one of these branches will execute, even if multiple conditions could be true.

Tips for using if/elif/else

• Order matters: put more specific conditions before more general ones.
• If two conditions can be true at the same time but you want both to execute, use separate if statements instead of elif.
• Keep conditions simple for readability; break complex checks into variables.

Quick practice

1. Classify a temperature as cold (< 0), cool (0–15), warm (16–25), or hot (> 25).
2. Given an integer 1–7, print the corresponding weekday name.
3. Given a test score 0–100, assign a letter grade using an if/elif/else cascade.

# 1) Temperature classification
t = int(input())
if t < 0:
    print("cold")
elif t <= 15:
    print("cool")
elif t <= 25:
    print("warm")
else:
    print("hot")

# 2) Weekday
day = int(input())
if day == 1:
    print("Monday")
elif day == 2:
    print("Tuesday")
elif day == 3:
    print("Wednesday")
elif day == 4:
    print("Thursday")
elif day == 5:
    print("Friday")
elif day == 6:
    print("Saturday")
else:
    print("Sunday")

# 3) Grade
score = int(input())
if score >= 90:
    print("A")
elif score >= 80:
    print("B")
elif score >= 70:
    print("C")
elif score >= 60:
    print("D")
else:
    print("F")