Problems

• hit_100
• even_squares
• roll_double
• university_challenge
• factor_test
• biggest
• fizzbuzz
• troll_count

Conditionals - If/Elif/Else

Basics

All of these problems require the use of conditionals. This is how our code makes decisions. In python, the syntax to do this looks like:

	if some criteria:
		do something

For example:

	if x == 5:
		print("x is 5!")

Important points:

• When asking whether two things are equal, we use a double equals ==
• Our if statement must end in a colon :
• The code we want to execute if the condition is true must be indented. We finish this block of code by moving the indentation back out.

Checking multiple conditions

If there are multiple options we want to check within the same decision block we can use if, elif, and else conditions. We must start with if, can have as many elif statements as we want and can, optionally, catch everything else with an else statement at the very end.

Example:

if x == 5:
	print("x is 5")

elif x >= 5:
	print("x is bigger than 5")

elif x > 0:
	print("x must be greater than 0 and less than 5")

else:
	print("x must be 0 or less")

By using elif and else we will only get to later statements if the earlier ones are not true. This is how we know, by the third statement (elif x > 0), that x must be between 0 and 5 - if x was 5 or bigger we would never have got to this point in the code.

More advanced conditions

We can use the keywords and and or if we need to test multiple conditions together on one line.

Example:

if x > 10 and x <= 20:
	print("bigger than 10 but less than or equal to 20")

Note: The conditions either side of an and or or have to be full questions.

Integer conditions

Some useful tests we can use with integers are:

• x == a - x equal to a
• x > a - x greater than a
• x < a - x less than a
• x >= a - x greater than or equal to a
• x <= a - x less than or equal to a
• a < x < b - x between a and b (we can use <= in here as well)

Another very useful test to use is to check whether something is divisible:

• x % 2 == 0 - test if x is divisible by 2