Chp-6: Iterations

Chp-6: Iterations#

Section Title: Iterations

Chapter Objectives

By the end of this chapter, the student should be able to:

Explain the purpose and role of iterations.
Use for and while loops for iterating over sequences.
Use the range function to generate sequences.
Apply loop control statements such as break and continue.
Apply iterations to solve real-world problems.

Motivation#

Triangle#

As a motivational exercise, let’s recall the code we previously encountered for printing a triangle using the & character and the print() function.

print('&')
print('&&')
print('&&&')
print('&&&&')
print('&&&&&')
print('&&&&&&')
print('&&&&&&&')
print('&&&&&&&&')
print('&&&&&&&&&')
print('&&&&&&&&&&')

&
&&
&&&
&&&&
&&&&&
&&&&&&
&&&&&&&
&&&&&&&&
&&&&&&&&&
&&&&&&&&&&

This code follows a pattern where the number of & characters increases by one in each line, simplifying the code through repetition.

print('&'*1)
print('&'*2)
print('&'*3)
print('&'*4)
print('&'*5)
print('&'*6)
print('&'*7)
print('&'*8)
print('&'*9)
print('&'*10)

&
&&
&&&
&&&&
&&&&&
&&&&&&
&&&&&&&
&&&&&&&&
&&&&&&&&&
&&&&&&&&&&

The second version, using string repetition, is simpler than the first.
However, further simplification is possible as there are still repetitions, such as the presence of the print() function in each line.
To address this, iterations can be employed to avoid using the print() function ten times.
Using iterations offers the following advantages:
- It eliminates repetition.
- It does not become longer even with a larger triangle
The iteration version is as follows:

for i in range(1,11):    # iteration
    print('&'*i)

&
&&
&&&
&&&&
&&&&&
&&&&&&
&&&&&&&
&&&&&&&&
&&&&&&&&&
&&&&&&&&&&

Strings#

We have explored various methods for working with strings, yet a crucial aspect remains unaddressed:
- how to iterate through all characters of a string individually.
While indexes and slices allow access to specific characters or portions of a string, the challenge lies in accessing each character sequentially.

Question: What is the occurrence of a certain character, such as ‘r’, in a string?
- How can we address this question without using the count() method of strings?
- The solution involves checking whether each character in the string matches ‘r’.

Let’s attempt to write code that answers this question using a short string and only the information we have gathered from the previous chapters.

text = 'radar'
count_r = 0

if text[0] == 'r':
    count_r += 1
if text[1] == 'r':
    count_r += 1
if text[2] == 'r':
    count_r += 1
if text[3] == 'r':
    count_r += 1
if text[4] == 'r':
    count_r += 1

print(f'There are {count_r} "r" characters in {text}.')

There are 2 "r" characters in radar.

As evident, there are numerous repetitions in this code, making it overwhelming for long strings.
To mitigate this, iterations can be employed to avoid the need for using the if statements multiple times.
The iteration version is as follows, it eliminates repetition and does not become longer even with an extended string.

text = 'radar'
count_r = 0

for char in text:            # iteration
    if char == 'r':          # Checking if the character is 'r'
        count_r += 1
    
print(f'There are {count_r} "r" characters in {text}.')

There are 2 "r" characters in radar.

Question: Now let’s work on a more complicated question. What are the digits in a string which are greater than 6?

Let’s attempt to write code that answers this question using a string which consists of digits and only the information we have gathered from the previous chapters.

text = '192736'
print(f'The digits in {text} which are greater than 6:')

if int(text[0]) > 6:
    print(text[0])
if int(text[1]) > 6:
    print(text[1])
if int(text[2]) > 6:
    print(text[2])
if int(text[3]) > 6:
    print(text[3])
if int(text[4]) > 6:
    print(text[4])
if int(text[5]) > 6:
    print(text[5])

The digits in 192736 which are greater than 6:
9
7

The code above shows repetition, which can be overwhelming for long strings.
The iteration version, provided below, eliminates this repetition and does not become longer even with an extended string.

text = '192736'
print(f'The digits greater than 6 in {text}:')

for char in text:
    if int(char) > 6:
        print(char)

The digits greater than 6 in 192736:
9
7

Iterations#

Iterations are used to perform the same or similar tasks in a more efficient way.

Similar tasks usually follow a pattern that can be used to write the code in a shorter and more readable way.

There are two types of iterations available in programming languages:

for loop: This is used for definite repetition, executing a code for a known number of times.
while loop: This is used for indefinite repetition, executing a block code for a possibly unknown number of times.

The for loop executes its block code repeatedly for every element of a sequence.
- It has a condition (boolean expression) with the in operator, making it possible to execute the block code only for elements of the sequence.
The while loop executes a block code as long as its condition is True.
- It is similar to an if statement because its condition can be any boolean expression (not only with in).
- The difference lies in the fact that the block code of an if statement is executed only once if the condition is True.
- In contrast, if the condition of the while loop is True, its block code is executed as in if statements, but then the condition is checked again.
- If it is still True, the block code will be executed again.
- The while loop keeps executing its block code as long as its condition becomes False or a break command is used to terminate it.

Range Function#

The built-in range() function returns a sequence of integers. It is a memory-efficient way of storing numbers.

The type of its output is range, and its values are hidden within it.
You can use the built-in list() function to explicitly display the numbers in a range type output.
The range() function has three important parameters: start, end, and step.
- How they work is similar to the start, end, and step used for slicing of strings or lists by using indexes.

There are three cases:

#	Function	Numbers	Explanation
1	range(a)	0, 1,2,…,a-1	integers starting from 0 goes upto a-1
2	range(a,b)	a, a+1, …, b-1	integers starting from a goes upto b-1
3	range(a,b,s)	a, a+s, a+2s, …, less than b-1	integers start from a go upto b-1 with an increment of s

The step \(s\) can be a negative number. If \(s\) is a negative number:
- If \(a < b\), the output is empty (as you cannot reach \(a\) from \(b\) by adding negative numbers).
- If \(a > b\), the output is \(a, a+s, a+2s \ldots ,\) less than \(b+1\) (as you can reach \(b\) from \(a\) by adding negative numbers).
Examples:
- range(10) consists of \(0, 1, 2, 3, 4, 5, 6, 7, 8, 9\).
- range(2,10) consists of \(2, 3, 4, 5, 6, 7, 8, 9\).
- range(2,10,3) consists of \(2, 5, 8\).
- range(2,10,-3) is empty.
- range(10,2,-3) consists of \(10, 7, 4\).

# Case 1: range(a)
rng_numbers = range(10)

print(f'Output: {rng_numbers}' )
print(f'Type  : {type(rng_numbers)}')
print(f'List  : {list(rng_numbers)}')

Output: range(0, 10)
Type  : <class 'range'>
List  : [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

# Case 2: range(a,b)
rng_numbers = range(2,10)

print(f'Output: {rng_numbers}' )
print(f'Type  : {type(rng_numbers)}')
print(f'List  : {list(rng_numbers)}')

Output: range(2, 10)
Type  : <class 'range'>
List  : [2, 3, 4, 5, 6, 7, 8, 9]

# Case 3: range(a,b,s)
rng_numbers = range(2,10,3)

print(f'Output: {rng_numbers}' )
print(f'Type  : {type(rng_numbers)}')
print(f'List  : {list(rng_numbers)}')

Output: range(2, 10, 3)
Type  : <class 'range'>
List  : [2, 5, 8]

# Case 3: a<b and negative s
rng_numbers = range(2,10,-3)

print(f'Output: {rng_numbers}' )
print(f'Type  : {type(rng_numbers)}')
print(f'List  : {list(rng_numbers)}')

Output: range(2, 10, -3)
Type  : <class 'range'>
List  : []

# Case 3: a>b and negative s
rng_numbers = range(10,2,-3)

print(f'Output: {rng_numbers}' )
print(f'Type  : {type(rng_numbers)}')
print(f'List  : {list(rng_numbers)}')

Output: range(10, 2, -3)
Type  : <class 'range'>
List  : [10, 7, 4]

Quick Check!

Find the output of the following code:

print(list(range(3)))
print(list(range(6, 9)))
print(list(range(5, 14, 3)))

Solution

[0, 1, 2]
[6, 7, 8]
[5, 8, 11]

for loop#

The structure of a for loop is as follows:

for i in sequence:

       BLOCK CODE

The outputs of the range() function and strings can be used as sequences.
- Each number in the output of the range() function will be an \(i\) value.
- Each character of the strings will be an \(i\) value.
\(i\) is the counter, and you can choose a different name for it.
For each \(i\) value from the sequence, the block code will be executed.
The output depends on what \(i\) does in the block code.

Example: In the code below the values of \(i\) are: \(3, 4, 5\).

The print statement will be executed for each \(i\) value one by one.
The squares of the \(i\) values will be printed.

iteration #	\(i\)	\(i^2\)
1	3	9
2	4	16
3	5	25

for i in range(3,6):
    print(i**2)

9
16
25

The for loop: for i in range(3, 6): print square of i works as follows:Since i is in the range (3, 6), the values of i will be 3, 4, and 5.When i = 3, the square of 3, which is 9, is displayed.When i = 4, the square of 4, which is 16, is displayed.When i = 5, the square of 5, which is 25, is displayed.

Example: In the code below the values of \(i\) are: \(1,2,3,...,10\)

In every iteration, \(i\) many & characters are printed.

iteration #	\(i\)	&*\(i\)
1	1	&
2	2	&&
3	3	&&&
4	4	&&&&
5	5	&&&&&
6	6	&&&&&&
7	7	&&&&&&&
8	8	&&&&&&&&
9	9	&&&&&&&&&
10	10	&&&&&&&&&&

for i in range(1,11):
    print('&'*i)

&
&&
&&&
&&&&
&&&&&
&&&&&&
&&&&&&&
&&&&&&&&
&&&&&&&&&
&&&&&&&&&&

Example: In the code below, the values of \(j\) are: \(3, 4, 5\).

The block code (4 lines) will be executed for each \(j\) value one by one.
The value of each frac variable is calculated as shown in the table below.
The calculated frac values will be printed.

iteration #	j	num = \(3\times j+2\)	den = \(10^j\)	frac=num/den
1	3	\(3\times 3+2=11\)	\(10^3=1,000\)	0.011
2	4	\(3\times 4+2=14\)	\(10^4=10,000\)	0.0014
3	5	\(3\times 5+2=17\)	\(10^5=100,000\)	0.00017

for j in range(3,6):
    num = 3*j+2
    den = 10**j
    frac = num/den
    print(frac)

011
0014
00017

Example: In the code below, the values of \(i\) are: ‘u’, ‘t’, ‘a’, ‘h’.

In every iteration, the value of \(i\), which is a character of ‘utah’ is printed.

for i in 'utah':
    print(i)

u
t
a
h

Example: In the code below, the values of \(i\) are: ‘u’, ‘t’, ‘a’, ‘h’.

The condition of the if statement is True if the value of \(i\) is before ‘k’ in dictionary order.
- This is False for ‘u’ and ‘t’, so they are not printed.
- This is True for ‘a’ and ‘h’, so they are printed.

for i in 'utah':
    if i < 'k':
        print(i)

a
h

Example: In the code below, the values of \(i\) are: \(3, 4, 5\).

The initial value of the \(total\) variable is \(0\).
In each iteration, the value of \(i\) is added to the \(total\).

iteration #	\(i\)	\(total\)
-	-	0
1	3	0+3=3
2	4	3+4=7
3	5	7+5=12

total = 0

for i in range(3,6):
    total += i
    print(f'Iteration number:{i-2}   i:{i}--->total:{total}')

Iteration number:1   i:3--->total:3
Iteration number:2   i:4--->total:7
Iteration number:3   i:5--->total:12

Quick Check!

Find the output of the following code:

for i in range(5):
    print(2*i)

Solution

0
2
4
6
8

Quick Check!

Find the output of the following code:

for i in 'Germany':
    if i < 'e':
        print(i)

Solution

G
a

break and continue#

break is used to terminate the for loop.

It is usually used in an if statement to terminate the for loop under certain conditions.

continue is used to skip the rest of the body code of the for loop.

It goes back to the beginning of the loop.
It does not terminate the loop, just skips the rest of the block code for that iteration.

Example: In the code below, the values of \(i\) are: \(1,2,3,4\).

for \(i=1\) and \(i=2\), the if part is not executed since its condition is False, and the values \(1\) and \(2\) are printed.
for \(i=3\), break is executed, and the loop is terminated.

for i in range(1,5):
    if i == 3: 
       break
    print(i)

1
2

Example: In the code below, the values of \(i\) are: \(1,2,3,4\).

For \(i=1\) and \(i=2\), the if part is not executed since its condition is False, and the values \(1\) and \(2\) are printed.
For \(i=3\), continue is executed, and the print statement is skipped, and the \(i=4\) iteration is started.
For \(i=4\), the if part is not executed since its condition is False, and the value \(4\) is printed

for i in range(1,5):
    if i == 3: 
       continue                
    print(i)     

1
2
4

Quick Check!

Find the output of the following code:

for i in range(100):
    print(2*i)
    if i == 3:
        break

Solution

0
2
4
6

for and else#

for loops can have an else statement.

The else statement is executed when the for loop is completed without any break.

Example: In the code below, the values of \(i\) are: \(1,2,3,4\).

After executing the print() function for \(i=4\), the for loop is over, and the else part is executed.

for i in range(1,5):
    print(i)
else:                 
    print('Over')     

1
2
3
4
Over

Example: In the code below, the values of \(i\) are: 1,2,3,4.

The condition of the if statement is True when \(i\) is 4, and the break is executed, so the for loop is terminated and the else part is not executed.

for i in range(1,5):
    print(i)
    if i> 3:
        break            
else:                 
    print('Over')     

while loop#

The while loops are similar to the if statements. In if statements, block code is executed only once when the condition is True, whereas in while loops, the block code might be executed more than once.

If the condition is True, the block code is executed as in if statements, but then the condition is checked again.
If it is still True, the block code of the while loop is executed again.
This process continues as long as the condition is True.
Whenever the condition becomes False, the while loop is terminated.

The structure of a while loop is as follows:

while condition:

       BLOCK CODE

condition is a Boolean expression (True or False)
Possible conditions:
- True, False;
- <, >, <=, >=, ==, !=
- not, and, or
- numbers, strings

Example: In the code below, the initial value of \(n\) is 3.

\(n=3\): Check the condition.
- Since \(3 > 0\), the condition is True, and the block code is executed.
- \(3\) is printed, and \(n\) becomes \(3 - 1 = 2\).
\(n=2\): Check the condition.
- Since \(2 > 0\), the condition is True, and the block code is executed.
- \(2\) is printed, and \(n\) becomes \(2 - 1 = 1\).
\(n=1\): Check the condition.
- Since \(1 > 0\), the condition is True, and the block code is executed.
- \(1\) is printed, and \(n\) becomes \(1 - 1 = 0\).
\(n=0\): Check the condition.
- Since \(0 > 0\) is False, the condition is False, and the loop is terminated.

iteration #	intial \(n\)	condition	\(n\) becomes
-	3	-	-
1	3	True	2
2	2	True	1
3	1	True	0
4	0	False	-

n = 3

while n>0:
    print(n)
    n -= 1

3
2
1

Example: In the code below, the initial value of \(n\) is \(3\).

n = 3

while n:
    print(n)
    n -= 1

3
2
1

Iterations:

\(n=3\): Check the condition.
- Since bool(3) is True, the condition is True, and the block code is executed.
- \(3\) is printed, and \(n\) becomes \(3-1=2\).
\(n=2\): Check the condition.
- Since bool(2) is True, the condition is True, and the block code is executed.
- \(2\) is printed, and \(n\) becomes \(2-1=1\).
\(n=1\): Check the condition.
- Since bool(1) is True, the condition is True, and the block code is executed.
- 1 is printed, and \(n\) becomes \(1-1=0\).
\(n=0\): Check the condition.
- Since bool(0) is False, the condition is False, and the while loop is terminated

Example: In the code below, the initial values are set with \(n=3\) and \(\text{total}=0\).

iteration #	intial \(n\)	initial total	condition	\(n\) becomes	total becomes
-	3	0	-	-	-
1	3	0	True	4	3
2	4	3	True	5	7
3	5	7	True	6	12
4	6	12	False	-	-

Quick Check!

Find the output of the following code:

n = 10

while n > 7:
    print(2*n)
    n -= 1

Solution

20
18
16

total = 0
n = 3
while n<6:
    total += n
    print(f'Iteration number:{n-2}   n:{n}--->total:{total}')
    n += 1

Iteration number:1   n:3--->total:3
Iteration number:2   n:4--->total:7
Iteration number:3   n:5--->total:12

Iterations:

\(n=3, \text{total}=0\): Check the condition.
- Since \(3 < 6\), the condition is True, and the block code is executed.
- \(\text{total} = 0 + 3 = 3\)
- print: Iteration number: 1 \(n:3 \rightarrow \text{total}:3\)
- \(n = 3+1 = 4\)
\(n=4, \text{total}=3\): Check the condition.
- Since \(4 < 6\), the condition is True, and the block code is executed.
- \(\text{total} = 3 + 4 = 7\)
- print: Iteration number: 2 \(n:4 \rightarrow \text{total}:7\)
- \(n = 4+1 = 5\)
\(n=5, \text{total}=7\): Check the condition.
- Since \(5 < 6\), the condition is True, and the block code is executed.
- \(\text{total} = 7 + 5 = 12\)
- print: Iteration number: 3 \(n:5 \rightarrow \text{total}:12\)
- \(n = 5+1 = 6\)
\(n=6, \text{total}=12\): Check the condition.
- Since \(6 > 6\) is False, the condition is False, and the while loop is terminated.

iteration #	\(n\)	\(total\)
-	-	0
1	3	0+3=3
2	4	3+4=7
3	5	7+5=12

if versus while#

In the following two examples, the same block code is used in an if statement and a while loop.

In the if statement, the block code is executed only once for \(n=3\).
In the while loop, the block code is executed two times for \(n=3\) and \(n=2\).

Example-1: In the code below, the condition of the if statement is True, and the block code is executed.

n = 3

if n > 1:
  print(n)
  n = n-1

The print statement is executed, and the value of \(n\), which is \(3\), is printed.
Afterward, \(n\) is updated to \(3-1=2\).
The if statement is then concluded, and the only output is 3.

Example-2: In the code below, the initial value of \(n\) is 3.

n = 3

while n > 1:
  print(n)
  n = n-1

3
2

Iterations:

\(n=3\): Check the condition.
- Since \(3 > 1\), the condition is True, and the block code is executed.
- \(3\) is printed, and \(n\) becomes \(3-1=2\).
\(n=2\): Check the condition.
- Since \(2 > 1\), the condition is True, and the block code is executed.
- \(2\) is printed, and \(n\) becomes \(2-1=1\).
\(n=1\): Check the condition.
- Since \(1 > 1\) is False, the condition is False, and the while loop is terminated.

Infinite Loop#

It is possible to have a condition for a while loop that is always True.

In that case, the block code will be executed repeatedly unless the program is terminated by the user.
This is not a syntax error, but it is not expected because the program will not end.

Example: In the code below, the initial value of \(n\) is \(3\), and in each iteration, \(n\) is increased by \(1\).

Hence, the values of \(n\) are: \(3, 4, 5, 6, \ldots\).
The condition \(n > 1\) is always True, and the while loop never terminates.

# infinite loop
n = 3

while n > 1:         # always True
  print(n)
  n = n+1            # n=3,4,5,......

Example: In the code below, the condition is always True.

‘Hello’ is printed repeatedly, and the loop never terminates.

# infinite loop

while True:         
  print('Hello')           

break and continue#

They work similarly to the for loop. To prevent infinite loops, the use of break is particularly crucial for while loops.

Example: In the code below the initial value of \(n\) is \(3\).

n = 3

while n > 1:
  print(n)
  n = n+1
  if n == 5:
      break

3
4

Iterations:

\(n=3\): Check the condition.
- Since \(3 > 1\), the condition is True, and the block code is executed.
- #3# is printed, and \(n\) becomes \(3+1=4\).
- \(3 \neq 5\), so the condition of the if statement is False, and the break statement is skipped.
\(n=4\): Check the condition.
- Since \(4 > 1\), the condition is True, and the block code is executed.
- \(4\) is printed, and \(n\) becomes \(4+1=5\).
- \(5 == 5\), so the condition of the if statement is True, and the break statement is executed.
- The while loop is terminated.

Examples#

Sum of Numbers#

Find the sum of the numbers \(1,2,3,...,100\) using

a for loop
a while loop
The formula for the sum of the first \(n\) positive integers: \(1+2+3+\ldots+n=\displaystyle \frac{n(n+1)}{2}\)

Solution

# for loop
total_for = 0
for i in range(1,101):
    total_for += i

# while loop
total_while = 0
n = 1
while n <= 100:
    total_while += n
    n +=1

#formula
total_formula = 100*(100+1)/2

print(f'for   loop answer: {total_for}')
print(f'while loop answer: {total_while}')
print(f'formula    answer: {total_formula}')

for   loop answer: 5050
while loop answer: 5050
formula    answer: 5050.0

Text Analysis#

For the given text below, find the number of occurrences of the character ‘t’ using:

a for loop
a while loop
a string method

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Solution

# for loop
count_for = 0
for char in text:
    if char == 't':
        count_for +=1

# while loop
count_while = 0
n = 0
while n < len(text):   # n values are the indexes
    if text[n] == 't':
        count_while +=1
    n += 1

# string method
count_method = text.count('t')

print(f'for   loop answer: {count_for}')
print(f'while loop answer: {count_while}')
print(f'method     answer: {count_method}')

for   loop answer: 267
while loop answer: 267
method     answer: 267

Reverse a word#

Write a program that reverses the given text below using:

a for loop
a while loop
indexing and step

text = 'How are you?'

Solution

# for loop
reverse_for = ''
for char in text:
    reverse_for = char + reverse_for

# while loop
reverse_while = ''
n = 0
while n < len(text):
    reverse_while = text[n] + reverse_while
    n += 1
# indexing
reverse_index = text[::-1]

print(f'for   loop answer: {reverse_for}')
print(f'while loop answer: {reverse_while}')
print(f'indexing   answer: {reverse_index}')

for   loop answer: ?uoy era woH
while loop answer: ?uoy era woH
indexing   answer: ?uoy era woH

Secret Number Game#

This is the updated version of the game in the conditionals chapter. In this new version, the user will keep guessing the number until quitting the game by entering \(0\).

Steps:

Choose a random integer between \(1\) and \(10\) as the secret number, and 0 to quit the game.
Ask for a number from the user to guess the secret number.
- If the user’s guess is correct, display ‘You win!’
- If the user’s guess is incorrect, display ‘Incorrect. Try again!’ and ask for a new guess.
- If the user’s input is \(0\), quit the game.
Use try and except to avoid errors if the user enters non-numeric values.
- Warn the user if there is an error by displaying a message.

Solution

import random
secret_number = random.randint(1,10)      # choose a random number between 1 and 10

while True:                               # it will keep asking for a guess from the user as long as there is no break

    try:
        player = int(input('Guess the secret number or press 0 to quit: '))
    
        if player == secret_number:
            print('Correct. You win!')
            break
        elif player == 0:
            print('Game is over!')
            break
        else:                                   
            print('Incorrect. Try Again!')          
    
    except:
        print('Please enter a valid numeric value!')

Sample Output:
Guess the secret number or press 0 to quit: 6
Incorrect. Try Again!
Guess the secret number or press 0 to quit: 3
Incorrect. Try Again!
Guess the secret number or press 0 to quit: 8
Correct. You win!

Factors-1#

Write a program that asks the user to enter a positive integer.

Display the positive factors of this number.
A factor of a number is a positive integer that divides the given number without leaving a remainder.
Example: The factors of \(12\) are \(1,2,3,4,6,12\).

Solution

n = int(   input('Enter a positive integer n:')  )
print(f'The factors of {n} are: ', end = '')

for i in range(1,n+1):       # factors are between 1 and the given number n
    if n%i==0:
        print(i, end=',')
        
print('\b') # remove the last comma 

Sample Output:
Enter a positive integer n: 12
The factors of 12 are: 1,2,3,4,6,12

Factors-2#

Write a program that asks the user to enter a positive integer.

Display whether the numbers between 1 and the given number are positive factors of the given number.

Solution

number = int( input('Enter a positive integer n:'))

for i in range(1, number+1):  # 1,2,3,4,5,6
  if number % i == 0:     # i is a factor
    print(f'{i} is a factor of {number}.')
  else:                   # i is not a factor
    print(f'{i} is NOT a factor of {number}.')

Sample Output:
Enter a positive integer n: 12
1 is a factor of 12.
2 is a factor of 12.
3 is a factor of 12.
4 is a factor of 12.
5 is NOT a factor of 12.
6 is a factor of 12.
7 is NOT a factor of 12.
8 is NOT a factor of 12.
9 is NOT a factor of 12.
10 is NOT a factor of 12.
11 is NOT a factor of 12.
12 is a factor of 12.

Countdown#

Write a program that counts down from \(3\) to \(0\) and displays these numbers with ‘START’ at the end.

Add one second between each output by using the sleep() method of the time module.
- time.sleep(1) delays the execution for \(1\) second.

Solution

import time

for i in range(3,-1,-1):
  print(i)
  time.sleep(1)
    
print('START')

Output:
3
2
1
0
START

Count digits#

Write a program that prints the digits greater than 6 in a given string, which may include any character.

Use a for loop and try-except.

text = 'a9b4dh6e1_%**8371__dthYFR8G12po7+'

Solution:

print(f'The digits greater than 6 in {text}:')

for char in text:
    try:
        if int(char) > 6:
            print(char)
    except:
        pass

The digits greater than 6 in a9b4dh6e1_%**8371__dthYFR8G12po7+:
9
8
7
8
7

Chp-6: Iterations

Contents

Chp-6: Iterations#

Motivation#

Triangle#

Strings#

Iterations#

Range Function#

for loop#

break and continue#

for and else#

while loop#

if versus while#

Infinite Loop#

break and continue#

Examples#

Sum of Numbers#

Text Analysis#

Reverse a word#

Secret Number Game#

Factors-1#

Factors-2#

Countdown#

Count digits#