Week 1 - REVISION¶

For Loops, While Loops and Function calls¶

For loops¶

for element in list:
    code inside the loop
code outside the loop

Break¶

Break means "stop the loop, don't do anymore iterations -- even if we weren't done yet"

Continue¶

Continue means "skip the rest of this iteration of the loop and start the next iteration"

Question 1. What will print in the code below?¶

for n in [1,2,3,4,5]:
    print (n)
print("\U0001F600")
for w in [1,2,3]:
    print(w)
print("lol - I do know my numbers")

1
2
3
4
5
😀
1
2
3
lol - I do know my numbers

Question 2. Print all numbers that are divisible by 3 and not by 2 in the range 20 to 40¶

for i in range(20,41):
    if i % 2 == 0:
        continue   # returns control to the beginning of the loop
    if i % 3 == 0:
        print(i)

21
27
33
39

Question 3. Print the number of even numbers in a given list¶

lst = [2,5,34,67,22,45,56]
nbr_even=0
for i in lst:
    if i%2 == 0:
        x = i%2
        nbr_even = nbr_even +1  #nbr_even + = 1
            
print(nbr_even)

4

While loops¶

while condition:
    code inside the loop
code outside the loop

If the condition is True, run the code in the while loop, and then start back at the beginning of the while loop.

If the condition is False, skip the code in the while loop.

#Find the square root of a given perfect square 

x= 16
ans = 0
while ans*ans < x: 
    print(f"Value of multiplication = {ans*ans}")
    print(f"   Incrementing loop variable {ans + 1}")
    ans += 1           # ans = ans + 1
print (ans)

Value of multiplication = 0
   Incrementing loop variable 1
Value of multiplication = 1
   Incrementing loop variable 2
Value of multiplication = 4
   Incrementing loop variable 3
Value of multiplication = 9
   Incrementing loop variable 4
4

print("S")
print("SS")
print("SSS")
print("S" * 1)
print("S" * 2)
print("S" * 3)

S
SS
SSS
S
SS
SSS

current_step = 1 # initialize counter
while current_step < 10: # condition
    print("clap " * current_step) # body
    current_step += 1 # increment counter current_step = current_step + 1

clap 
clap clap 
clap clap clap 
clap clap clap clap 
clap clap clap clap clap 
clap clap clap clap clap clap 
clap clap clap clap clap clap clap 
clap clap clap clap clap clap clap clap 
clap clap clap clap clap clap clap clap clap

Question 4. Print all the even numbers through 20 using a while loop.¶

EX: 0, 2, 4, ... 20

i = 0
while i < 21:
    if i % 2 == 0:
        print(i)
    i += 1

Question 5. Print all the odd numbers through 20 using a while loop.¶

EX: 1,3,5, . . . 19

i = 0 
while i < 21:
    if i % 2 != 0:
        print(i)
    i += 1

Question 6. Print all the even numbers until n.¶

n = 5
i = 0
while i < n:
    if i % 2 == 0:
           print(i)
    i += 1

0
2
4

Functions¶

We decide how many arguments a function has when we define it

def function_name(arg1, arg2):
    if arg1 == "":
        if arg2 == "":
            return None
    return arg1+" " +arg2

print(function_name("Hello", "again")) 
function_name("Hello", "again") + ", nice to see you"

Hello again

'Hello again, nice to see you'

def even(lst):
    nbr_even=0
    for i in lst:
        if i%2 == 0:
            x = i%2
            nbr_even = nbr_even +1  #nbr_even + = 1
    return nbr_even

even([2,5,34,67,22,45,56,44])  # try and put +1

5

print(even([2,5,34,67,22,45,56,44])) #try and put +1

5

# This is an example of a function with two arguments

def sumTwo(x, y):
    return x + y

sumTwo(1, 2)

3

sumTwo(sumTwo(4,5), sumTwo(2,3)) + 5

19

# You can have functions that call functions

def sumThree(x, y, z):
    return x + sumTwo(y, z)

sumThree(1, 2, 3)

6

# You can have functions that call functions that call functions

def sumFour(a, b, c, d):
    return a + sumThree(b, c, d)

sumFour(1, 2, 3, 4)

10

What happens if there are two return statement in a function?

Now see a function that calls itself!!

def factorial(n):
    if n == 1:
        return 1
    else:
        return n * factorial(n - 1)
    
    
def factorial2(n):
    if n==1: 
        return 1
    return n * factorial(n-1)

print(factorial(5))
print(factorial2(5))

120
120

# Definition of factorial: n! = n * (n - 1) * (n - 2) * ... * 3 * 2 * 1
# Also, 1! = 1
# How can you turn this into a recursion?
# Recursive case: 
# Base case: 1! = 1
#n! = n * (n - 1)!

For example:

$f(x) = x$

$g(x,y) = x + y$

$h(x,y,z) = x+y+z$

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