🔁 Loop Control — Sentinel vs Counter

🛑 Sentinel-Controlled Loop

Used when the number of iterations is unknown. Loop continues until a special value (sentinel) is encountered.

sentinel = -999
total = 0

num = int(input("Enter a number (-999 to stop): "))
while num != sentinel:
    total += num
    num = int(input("Enter a number (-999 to stop): "))

print("Total sum:", total)

🔍 Termination is data-driven, not count-driven.

🔢 Counter-Controlled Loop

Used when the number of iterations is known in advance. Loop runs a fixed number of times.

total = 0

for i in range(5):
    num = int(input(f"Enter number {i+1}: "))
    total += num

print("Total sum:", total)

🔍 Termination is count-driven, not data-triggered.

🧠 Semantic Summary

🧩 Use sentinel loops for indefinite repetition, and counter loops for bounded iteration. Document clearly to avoid semantic drift.