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Software ==>	Python (34 exercises)
Topic ==>	Ranges and loops (5 exercises)
Level ==>	Harder than average
Subject ==>	Python training

Use the range function in an outer loop to find all the primes up to 100 using an inner loop

This exercise is provided to allow potential course delegates to choose the correct Wise Owl Microsoft training course, and may not be reproduced in whole or in part in any format without the prior written consent of Wise Owl.

A prime number is one which is only divisible by itself and 1 (so 23 is a prime, but 21 isn't because it's also divisible by 3 and 7). The aim of this program is to print out the first N primes:

N can be any number you choose (there are an infinite number of primes, so you won't run out ...).

Create a program call Prime numbers to loop over the integers from 2 up to 100.

Within this loop, set the value of a variable called if_prime to be True.

This is a common programming tactic: you assume something is true for each time round a loop, then try to disprove it.

Within the outer loop, write an inner loop which loops from 2 up to a number 1 less than the outer loop integer. For each time round the inner loop you should test if the inner loop integer exactly divides the outer loop one:

Use syntax like this to see if when you divide one number by another you get a remainder of zero.

If the inner loop integer does exactly divide the outer loop one, this number wasn't a prime, so you should:

Set the value of if_prime to be False; then
Use the break command to break out of your loop.

If your program finishes the inner loop with the value of if_prime still set to True it must mean that the outer loop integer was prime, so print out its value.

Be very careful with your indentation! One feature of Python is that pressing Tab or Shift + Tab key to indent or unindent a line of code can completely change the way a program behaves.

When you're happy your program is working you could change it to loop over the first million integers, and have a well-earned coffee break ...

You can unzip this file to see the answers to this exercise, although please remember this is for your personal use only.

You can find other training resources for the subject of this exercise here:

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