for_loops.md

Repeating instructions

So far, each Python instruction was executed only once. That makes programming a bit useless, because our programs are limited by our typing speed.

In this section you will learn the for statements that repeats one or more instructions several times.

Warming up

What does the following program do?

for char in 'Emily':
    print(char)

What advantages does this (apparently more complex) program have over this one:

print('E')
print('m')
print('i')
print('l')
print('y')

Exercises

Exercise 1

What does the following program do?

text = ""
characters = "Hannah"
for char in characters:
    text = char + text
print(text)

Exercise 2

Write a for loop that creates the following output

000
111
222
333
444
555
666
777
888
999

Exercise 3

Write a for loop that creates the following string variable:

000111222333444555666777888999

Exercise 4

Write a for loop that creates the following output

1
3
6
10
15
21
28

Exercise 5

Write a for loop that creates the following string

"1 4 9 16 25 36 49 64 81 "

Exercise 6

Add a single line at the end of the program, so that it creates the following string:

"1 4 9 16 25 36 49 64 81"

Exercise 7

Which of these for commands are correct?

• for char in "ABCD":
• for i in range(10):
• for num in (4, 6, 8):
• for k in 3+7:
• for (i=0; i<10; i++):
• for var in seq:

The Challenge: count characters

Write a program that calculates the number of characters in Emily Smith.

Extra challenge

• Duplicate each character, so that Emily becomes EEmmiillyy.