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AQA Computer Science :: Cheat Sheet
Programming Technique :: Loops
Technique: Loops
“Looping may be referred to as repetition or iteration. We can use
loops in our programs for lots of different reasons. They help make code
more efficient because they require less code to perform the same
process.”
Increasing Efficiency with Loops
Here is some simple Python code for the numbers 1 to 10:
print
print
print
print
print
print
print
print
print
print
1
2
3
4
5
6
7
8
9
10
This takes a long time to write and it uses a lot of lines of code!
To make this more efficient we can use a loop. Here is how we can
make this more efficient using a for loop:
For the time that x is
between 0 and 10
Assigns 0 to the
variable number
x is just a temporary
variable that we use
for counting
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Add 1 to whatever is
stored in number
Display the content of
number
AQA Computer Science :: Cheat Sheet
Programming Technique :: Loops
We use a “for loop” when we need to count the number of times a
snippet of code will run.
If we want something to repeat while a condition is true, we can use a
while loop. We would use a while loop when we want to check if the
condition is true before the snippet of code is run.
Using the same example as above, we can create a while loop:
Assigns 0 to the
variable number
Keep doing this while
number is not equal to
10
Another type of loop is a repeat loop. A repeat loop will keep running
until a condition becomes true. This means that the condition is
checked at the end of the loop. You may see repeat until in some
programming languages. Python doesn’t use repeat, you can use…
while True:
…as an alternative.
AQA Pseudo Code
This is how these loops look in AQA pseudo code:
A While Loop
WHILE myVar < 10
OUTPUT myVar
myVar = myVar + 1
ENDWHILE
A For Loop
FOR x  1 to 10
OUTPUT i
ENDFOR
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AQA Computer Science :: Cheat Sheet
Programming Technique :: Loops
A Repeat…Until Loop
REPEAT
OUTPUT “Hello”
UNTIL myVar = 3
Test Yourself
Try creating a loop in Python that displays the 10 times table on the
screen.
HINT:
You may not know this…
If you need to display a variable within some text you can use this code
below:
name = “Becky”
print "Hello %s, how are you today?" %(name)
The %s symbol will be replaced with the variable mentioned at the end in
the brackets. This piece of code would output as:
Hello Becky, how are you today?
Computer Science @ Kingswinford