Iteration (AQA GCSE Computer Science)

Iteration

Pseudocode

Python

FOR loop

(Definite Iteration)

FOR x ← 0 to 9

OUTPUT("Hello")

ENDFOR

for x in range(10):

print("Hello")

This will print the word "Hello" 10 times (0-9 inclusive)

FOR x ← 2 to 10 step 2

OUTPUT(x)

ENDFOR

for x in range(2,12,2):

print(x)

# Python range function excludes end value

This will print the even numbers from 2 to 10 inclusive

for x ← 10 to 0 step -1

OUTPUT(x)

ENDFOR

for x in range(10,-1,-1):

print(x)

# Python range function excludes end value

This will print the numbers from 10 to 0 inclusive

WHILE loop

(Indefinite Iteration)

while colour != "Red"

colour ← input("New colour")

ENDWHILE

while colour != "Red":

colour = input("New colour")

This will loop until the user inputs the colour "Red". Check condition is carried out before entering loop

DO WHILE loop

(Indefinite Iteration)

DO

colour ← input("New colour")

UNTIL answer == "Red"

# Not used in Python

This will loop until the user inputs the colour "Red". Loop iterates once before a check is carried out