1. Task: print all prime numbers between 1 and 100 (2, 3, 5, 7, 11, 13, ...).
  2. You already know how to check one number: count factors; if count == 2, it's prime.
  3. Idea: loop n from 1 to 100; for each n, do the prime check; if prime, print n.
  4. So "prime check" is inside an outer loop over n.

Let’s go! 🚀

Part 1: Recall – How to Check One Number

📌 For a single number n:

count = 0
for i in range(1, n + 1):
    if n % i == 0:
        count += 1
if count == 2:
    # n is prime (only factors 1 and n)

Part 2: From 1 to 100 – Add an Outer Loop

📌 We want to check every n from 1 to 100. So we put the whole prime-check inside:

for n in range(1, 101):    # 1 to 100 inclusive
    count = 0
    for i in range(1, n + 1):
        if n % i == 0:
            count += 1
    if count == 2:
        print(n)

range(1, 101) gives 1, 2, 3, ..., 100. For each n we count factors; if count is 2, we print n.

Part 3: Demo – Primes from 1 to 30 (Short)

Primes from 1 to 30:

for n in range(1, 31):
    count = 0
    for i in range(1, n + 1):
        if n % i == 0:
            count += 1
    if count == 2:
        print(f"   {n}", end=" ")

Output:

2 3 5 7 11 13 17 19 23 29

Part 4: Summary

✅ Outer loop: n from 1 to 100 → for n in range(1, 101)

✅ Inner logic: same as single prime check (count factors; if count == 2, prime).

✅ If prime: print(n). No need to print not-prime for other numbers.

Congratulations! You now understand how to Print Prime Numbers from 1 to 100 in Python! 🎉

Key Takeaways:

  • Reuse your single-number prime check inside an outer for loop
  • range(1, 101) covers 1 to 100
  • Total work: 100 outer loops × (average ~50 inner checks)
  • This is the foundation for any range-based prime finder

Next Steps:

  • Make it faster: check only up to √n (we’ll learn optimization soon)
  • Add user input (ask for range 1 to N)
  • Print primes in a nice table or list