start of day 2

week 1/day 2/readme.md

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+# Day 2
+
+## Exercises (Submit for Grading)
+
+### Exercise 1 — Even / Odd
+
+Ask for a number and print:
+
+"Even" or "Odd"
+
+use: 
+```python
+n % 2
+```
+
+## Exercise 2 — Count Letters
+
+Given a string:
+
+count only alphabetic characters
+
+ignore digits and symbols
+
+## Exercise 3 — Rebuild Your C Validator (Python)
+
+Write your own version (no copy-paste):
+
+≤ 20 characters
+
+starts with letter
+
+no digits
+
+no spaces
+
+## Exercise 4 — Real-World Scenario
+
+Given:
+
+users = ["admin", "root1", "John_Doe", "Alice", "Bob42"]
+
+Print only valid usernames.
+
+Exercise 5 — Algorithm Explanation (Text)
+
+Answer:
+1. What happens to runtime if the list doubles in size?
+
+2. Write the formula.
+
+Expected:
+
+T(n) = c × n
+
+Explain in words.