مقدمة إلى الحلقات المتداخلة (Nested Loops)

You need to use a for loop inside a for loop.

You need the numbers from 1 to 12.

Whenever you need a sequence of consecutive numbers, use range.

You want something like for x in range(n):.

This will start with x = 0, but there's an easy workaround for that.

You can just add 1 to x.

Use * to multiply numbers.

Use an f-string with several variables.

Remember to print a line with the correct number of dashes after each section.

Make sure each line is in the correct loop and has the right amount of indentation.

Think about how you would do this manually and systematically, with a pencil and paper.

You need to use a for loop inside a for loop.

You need an if statement to check that the two players aren't the same person.

Think about how you would do this manually and systematically, with a pencil and paper.

The fact that the password must be four letters long is very important. This would be a lot harder to solve if the password could be any given length.

But the string letters might have any number of characters.

If there are n different letters, then the number of possible passwords is n^4 == n*n*n*n because there are n possible letters for each position and they're all independent.

Suppose again that letters = "ABCD". Imagine you have all possible three-letter passwords. Now for each one, add an A at the end, or add a B, or a C, or a D. That's how you would get all possible four-letter passwords.

Remember, a for loop can contain any statement, including another for loop.

That applies to all for loops.

One for loop inside another for loop is no longer enough.

You have to go deeper.

How would you describe instructions to type in this triangle manually?

Print a line of size plus signs, then size - 1 plus signs, etc. down to 1 plus sign. For example print 5 +s, then 4 +s, then 3, 2, and 1.

Break this down into subproblems.

How do you print one line of +s of a given length, and how do you go through all the lengths?

Building up a line of characters should be very familiar from previous exercises, the only difference is that you have to make it a given length instead of just the same length as another string.

An easy way to do something n times is to loop over range(n).

You need to use a for loop inside a for loop.

You need numbers that count down, like 5, 4, 3, 2, 1. There is a way to do this with range, and you can easily look it up, but it's also easy to use a normal range and do some very simple maths to convert numbers counting up into numbers counting down.

What formula converts 0 into 5, 1 into 4, 2 into 3, etc?

You'll need a for loop inside a for loop like before.

This time something like for player1 in players: won't be enough.

Your program needs to use the positions of the players in the list.

That means you need to loop over the positions and use indexing (subscripting) to access the list entries.

To loop over the positions, use range...

...and len.

Look at the desired output: Charlie vs Alice: Charlie comes before Alice in the players list.

We don't want to print Alice vs Charlie because Alice comes AFTER Charlie in players.

The only pairs we want to print are those where the left player comes before the right player in the list.

How can we express this relation in terms of the list indices of the two for-loops?

You need to use a comparison operator.

Once you figure out the relation, you can express it with an if statement.