Chapter -9 (While loops)

For learn how to download and install python link here: How to download and install python in window

For learn how to run and execute the code in python link here:How to write and run the code

In this blog, the format is first I write Code then Result of that code. You can directly copy the code and so your time save in written that code. Also , image of the code and result and after which it contain explanation of the code.

Example-1.1: To convert Celsius into Fahrenheit

Code:

temp=eval(input('Enter a temperature in Celsius:'))

print('In Fahrenheit, that is', 9/5*temp+32)

Result:

Enter a temperature in Celsius: 10

In Fahrenheit, that is 50.0

Explanation:- You see this example in chapter 1.

Example-1.2: Alternative to write the example-1

Code:

temp=eval(input('Enter a temperature in Celsius:'))

if temp<-273.15:

     print('That temperature is not possible.')

else:

     print('In Fahrenheit, that is', 9/5*temp+32)

Result:

Enter a temperature in Celsius: 10

In Fahrenheit, that is 50.0

<When you restart the shell>

Enter a temperature in Celsius: -273.15

In Fahrenheit, that is -459.66999999999996

<When you restart the shell>

Enter a temperature in Celsius: -274

That temperature is not possible.

Explanation:- You read this in previous chapter 2.

Example-1.3: Alternative to write the example-1

Code:

temp = eval(input('Enter a temperature in Celsius: '))

while temp<-273.15:

temp = eval(input('Impossible. Enter a valid temperature: '))

print('In Fahrenheit, that is', 9/5*temp+32)

Result:

Enter a temperature in Celsius: 20

In Fahrenheit, that is 68.0

<When you restart the shell>

Enter a temperature in Celsius: -274

Impossible. Enter a valid temperature:

Explanation:- Here we use while loop that means (in Hindi: jab tak)

means this loop repeat continuously until the temperature we input is less than -273.15 , unless this loop continuously ask question.

Example-2.1: While loop use

Code:

temp = 0

while temp!=-1000:

temp = eval(input('Enter a temperature (-1000 to quit): '))

print('In Fahrenheit that is', 9/5*temp+32)

Result:

Enter a temperature (-1000 to quit): 500

In Fahrenheit that is 932.0

Enter a temperature (-1000 to quit): 1000

In Fahrenheit that is 1832.0

Enter a temperature (-1000 to quit): -1000

In Fahrenheit that is -1768.0

Explanation:- While loop means this loop continuous work until temperature is not equal to 1000.This loop continuous ask question until temperature we enter -1000

<Symbol of not equal to: =! >

Example-2.2: In previous example it not show any message when exit the shell. Now to add message here another code.

Code:

temp = 0

while temp!=-1000:

temp = eval(input('Enter a temperature (-1000 to quit): '))

if temp!=-1000:

    print('In Fahrenheit that is', 9/5*temp+32)

else:

    print('Bye!')

Result:

Enter a temperature (-1000 to quit): 500

In Fahrenheit that is 932.0

Enter a temperature (-1000 to quit): 1000

In Fahrenheit that is 1832.0

Enter a temperature (-1000 to quit): -1000

Bye!

Explanation:- It is similar to previous example so you easily understand it.

Example-3: Write a program and ask the user to enter number between 1 and 10 and aks the number until the user get the right answer.

Code:

from random import randint

secret_num = randint(1,10)

guess = 0

while guess != secret_num:

     guess = eval(input('Guess the secret number: '))

print('You finally got it!')

Result:

Guess the secret number: 1

Guess the secret number: 2

Guess the secret number: 3

Guess the secret number: 4

Guess the secret number: 5

Guess the secret number: 6

Guess the secret number: 7

Guess the secret number: 8

Guess the secret number: 9

You finally got it!

Explanation:- You understand easily it is similar to previous chapter.

Example-4: Print the counting from 1 to 9

Code:

i=0

while i<10:

     print(i)

     i=i+1

Result:

1

2

3

4

5

6

7

8

9

Explanation:- In 1st line use i=0 because if we not use this it show error in 2nd line where we write i<10:, Then it not able to find the 'i'

<If you want to write by using for loop>

Code:

for i in range(10):

    print(i)

Example-5: Write a program and write counting by adding 2.

Code:

i=0 

while i<50:

     print(i)

     i=i+2

print('Bye')

Result:

0

2

4

6

8

......

Explanation:- In case of use for loop use:

<Code:

for i in range(25):

    print(2*i)

It give same result as the above but you know all way to write the code.>

Example-6: Print loop continuously

Code:

i=0

while i<10:

     print(i)

Result:

0

0

0

0....

Explanation:- Here in 1st line, i=0 and in 2nd line i<10 is true so the loop continuous repeat. To stop use 'Ctrl+C'

Example-7.1: Program that allows the user to enter up to 10 numbers. User stop by entering a negative number.

Code:

for i in range(10):

    num = eval(input('Enter number: '))

    if num<0:

        break

Result:

Enter number: 2

Enter number: 4

Enter number: -1 > Here exit

Explanation:- Here in 3rd line your see command if num<0: then in 4th line we write break means if it written negative number i.e., less than 0 then it exit.

Example-7.2: Program that allows the user to enter up to 10 numbers. User stop by entering a negative number.

Code:

i=0

num=1

while i<10 and num>0:

     num=eval(input('Enter a number:'))

Result:

Enter a number: 5

Enter a number: 4

Enter a number: -1

Explanation:- In first line we use i=0 and in 2nd num=1, if these not use here then in 3rd line while using i and num, python show error.

<Simply understand while by its hindi meaning 'jab tak', jab tak value code ko satisfy kregi tab tak while command kam kregi otherwise exit ho jayegi>

Example-7.3: Write a program and take the input from the user if user enter a negative number then exit.

Code:

for i in range(10):

    num=eval(input('Enter number:'))

    if num<0:

        print('Stopped early')

        break

else:

     print('User entered all ten values')

Result:

Enter number: 5

Enter number:4

Enter number:1

Enter number:-1

Stopped early

Explanation:- It is simple and copy of previous example, this is alternative to write the previous code.

Example-8.1: Write a program and find whether the number is prime or non prime.

Code:

num=eval(input('Enter your number:'))

for i in range(2,num)

     if num%i==0:

         print('Not prime')

         break

else:

    print('Prime')

Result:

Enter your number: 5

Prime

Enter your number:45

Not prime

Explanation:- First understand what is prime, prime number are those which are divide by itself or 1.

In 2nd line you see (2,num), here we write 2, not 1 because every number divide by 1.

In the 3rd line your see % it means remainder.

<num%i==0 means as an example if we take i.e., 5 then this shell divide the number first by 2 then 3 then 4 not 5 because in range last number not include, and as we know 5 not complete divide by 2,3,4 so this number is prime.>

Example-8.2: Write a program and find whether the number is prime or non prime.

Code:

i=2

num=eval(input('Enter your number:'))

while i<num and num%!=0:

      i=i+1

if i==num:

    print('Prime')

else:

    print('Not prime')

Result:

Enter your number:5

Prime

<If restart the shell>

Enter your number: 45

Not prime

Explanation:- It is alternative to previous example in this we use while, and in previous example use for loop.

Example-9.1: Write a program and ask user to enter some number between 1 and 100 and if guess is right then print you got it. User got only 5 chance to guess the number.

Code:

from random import randint

num=randint(1,100)

guess=0

count=0

while guess!=num and count<=4:

      guess=eval(input('Enter your guess (1-100): '))

      count=count+1

      if guess < num:

          print('HIGHER.', 5-count, 'guesses left.\n')

      elif guess> num:

          print('LOWER.', 5-count, 'guesses left.\n')

      else:

          print('You got it!')

if guess==5 and guess!= num:

   print('You lose. The correct number is', num)

Result:

Enter your guess (1-100): 15

HIGHER. 4 guesses left.

Enter your guess (1-100): 90

HIGHER. 3 guesses left.

Enter your guess (1-100):99

LOWER. 2 guesses left.

Enter your guess (1-100):50

HIGHER. 1 guesses left.

Enter your guess (1-100): 15

HIGHER. 0 guesses left.

Explanation:- In the 3rd and 4th line you see guess and count if you not use this then it show error.

In the 5 the line you see while command in which it say if guess is not equal to num and count is less than and equal to 4 ,until this process continue.

<You see 5-count means it minus 1 when you input your guess>

Example-9.2: Write a program and ask user to enter some number between 1 and 100 and if guess is right then print you got it. User got only 5 chance to guess the number.

Code:

from random import randint

num=randint(1,100)

count=0

for num in range(5):

    guess=eval(input('Enter your guess (1-100):'))

    count=count+1

    if guess<num:

         print('HIGHER.', 5-count, 'guesses left.\n')

    elif guess >num:

         print('LOWER', 5-count, 'guesses left.\n')

    else:

         print('You got it!')

         break

else:

     print('You lose. The correct number is', num)

Result:

Enter your guess (1-100): 50

LOWER. 4 guesses left.

Enter your guess (1-100): 10

LOWER. 3 guesses left.

Enter your guess (1-100): 50

LOWER. 2 guesses left.

Enter your guess (1-100): 70

LOWER. 1 guesses left.

Enter your guess (1-100): 30

LOWER. 0 guesses left.

You lose. The correct number is 4.

Explanation:- It is similar to previous example but it include for loop and in previous example we see while command.

Practice Question: