Loop Tutorials in Python,For,While,For--else,While--else example in Python

It is used to print range-based data using a common repeatable block. It is also called an iterative statement because it is used to enumerate data of LIST, Tuple, Dictionary, Set, and Database objects.
for example, if we want to print data from 1 to 1000 then we will prefer a loop statement.
1) While Loop Example in Python:-

 2) For Loop in Python:-

3) Nested For Loop in Python with Example:-

Flow of Loop
1    Forward     i=min      i<=max      i=i+1                  range(min,max)
2    Backward   i=max     i>=min      i=i-1                  range(max,min,-1)
3    Infinite       i=min,max  ,no condition, i=i+1,i=i-1

Type of Loop:-

1)  while loop and while--else loop:-
it will provide all statements of loop separately and it is mainly used to create an infinite condition-based program.

Syntax of While Loop:-

init;   

while(condition):
     Statement
     Increment
The direction of Loop Statements:-

Forward                        Backward

i = min                          i=max

i<= max                        i>=min

i = i+1                          i=i-1

Q) WAP to print 1 to 10?

i=1
while(i<=10):
   print(i)
   i=i+1
Q) WAP to print 10 to 1?

i=10

while i>=1:

    print(i)

    i=i-1

Q) WAP to print a table of any entered number?

num=int(input("enter number to caculate table"))

i=1

while(i<=10):

    print(str(num) + "*"+ str(i) + "=" + str(num*i))

    i=i+1

Q) WAP to print 1 to 5 and  5 to 1 using a single while loop?

1
2
3
4
5
5
4
3
2
1

Solution:- 

i=1
while(i<=10):
    if i<=5:
      print(i)
    else:
      print(11-i) 
    i=i+1

WAP to calculate square and cube of one digit positive number?
1      1       1
2      4       8
3      9      27

...

Solution:-

start = int(input("enter starting point"))
end = int(input("enter ending point"))
i=start
while(i<end):
    s=i*i
    c=i*i*i
    print(i,s,c)
    i=i+1

Infinite While Loop Based Program?

Q) Print String char till the end with Infinite while Loop?

flag=True

s = "adhfg djag fhjdg hfjgd jhf gdjfg djg fhd gfhdg jhfgdjfghjdgfhddjh f ghdjsgfhjd gfhjdsg hfj dshf"

c=0

while flag:

    print(s[c])

    c=c+1

    if c==len(s):

        flag=False

Another way to terminate infinite loop:-

s = "adhfg djag fhjdg hfjgd jhf gdjfg djg fhd gfhdg jhfgdjfghjdgfhddjh f ghdjsgfhjd gfhjdsg hfj dshf"

c=0

while True:

    print(s[c])

    c=c+1

    if c==len(s):

        break

Assignment of While Loop 

Q)WAP to calculate square and cube of one digit positive number?

Q)WAP to print 1 to 5 and  5 to 1 again 1 to 5 and 5 to 1 using a single while loop?

Solution of this assignment:-

import time

i=1

while i<=20:

    if i<=5:

        print(i)

    elif i<=10:

        print(11-i)

    elif i<=15:

        print(i-10)

    else:

        print(21-i)

    i=i+1    

    time.sleep(1)

Q)WAP to perform the addition of a one-digit positive number?   

1 to 9 = 55

sum=0

i=1

s= ''

while i<10:

    sum=sum+i

    if i<9:

     s = s + str(i) + "+"

    else:

     s = s + str(i) + "="   

    i=i+1

print(s,sum)

Q)WAP to calculate factorial of a number with complete expression? 

hint:-  factorial of five

5*4*3*2*1=120

The solution to this program:-

num = int(input("Enter number to calculate factorial"))

i=num

f=1

while i>=1:  # 0>=1  False

   f = f*i   # f = 120*1 120

   i= i-1    # i =0

print("factorial is ",f)    

Q) WAP to check the prime number?

The solution to this program:-

Solution First to check the divisibility of number from 1 to number?

num = int(input("enter number to check prime"))

count=0

i=1

while i<=num:

    if num%i==0:

        count=count+1

    i=i+1

if count==2:

    print("prime")

else:

    print("not prime")

Solution 2:-  

num = int(input("enter number to check prime"))

i=2

count=0

while i<num:

    if num%i==0:

        count=1

        break

    i=i+1

if count==0:

    print("prime")

else:

    print("not prime")

  

Solution 3:-

num= int(input("enter number"))

i=2

if num>1:

 while i<num:

    if num%i==0:

        print("not prime")

        break

    i=i+1    

 if num==i:

     print("prime")

else:

    print("Invalid number")

   

Solution 4:-

num= int(input("enter number"))

i=2

if num>1:

 while i<num//2:

    if num%i==0:

        print("not prime")

        break

    i=i+1    

 if num//2==i or num==2 or num==3:

     print("prime")

else:

    print("Invalid number")

Solution 5:-

# WAP to check prime number without using third variable

num= int(input("Enter any number")) #9

i=2

if num>2:

    if num%2==0:

        print("not prime")

    else:    

      while i<num//2:

         if num%i==0:

            print("not prime")

            break

         i=i+1 

      if num//2 == i or num==2 or num==3:

        print("prime")

Q)WAP to reverse any digit number?

hint, for example, user enter 54326   then the output will be 62345

num = 8770254643

s = ""

while num!=0:   # 87702546!=0

    a = num%10   #4

    num=num//10  # 8770254

    s = s +str(a) # 344

print(s)    

Q) WAP to find max digit, second max digit in mobile number?

hint:-  for example users enter 12345 then the output will be maxed 5 and the second max will be 4.

a= 681236783
8
7
The solution to this program:-

num = int(input("enter mobile number"))

m=0

sm=0

while(num!=0):

    rev = num%10

    print(rev)

    num = num//10

    if m<rev:

        sm=m

        m=rev

    elif sm<rev and num!=m:

        sm=rev

print(m,"",sm)  

 

Q) WAP to find max digit, second max digit, third max digit in mobile number?

mobile = int(input("Enter mobile number")) #154

maxmobile=0

smaxmobile=0

tmaxmobile=0

while mobile!=0:

    num = mobile%10    #1

    if maxmobile<num:  # 5<1

        tmaxmobie=smaxmobile #0

        smaxmobile=maxmobile #4

        maxmobile=num  # 5

    elif smaxmobile<num: #4<1

        tmaxmobile=smaxmobile

        smaxmobile=num   #

    elif tmaxmobile<num: #0<1

        tmaxmobile=num   #1

    mobile = mobile//10  #0

print(maxmobile,smaxmobile,tmaxmobile)    

    

Example of While else:-

Else statement is always used with if statement but in a python script, we can use else statement with a while and for loop both. Else block will be executed when the loop condition will false.

#while else example

WAP to reverse number?

num = int(input("enter number"))

s=''

while num!=0:

    s=s+str(num%10)

    num=num//10

else:

    print(s)

Q) WAP to check prime number using While--else statement in Python?

num = int(input("enter number to check prime"))

i=2

while i<num:

    if num%i==0:

        print("not prime")

        break

    i=i+1

else:

    print("prime")

WAP to calculate factorial of any number?

num = int(input("enter number to calculate factorial"))

f=1

i=num

s=''

while i>1:  # i=num;i>1;i--

    f=f*i  #f=5 20  60 120

    s=s+str(i)+"*"

    i=i-1

print("factorial is ",s+"1=",f)    

Infinite While Loop:-

If we provide a condition that is not determined initially then we use an infinite while loop.

Syntax:-

while True:

     Statement

while True:

    print("Ram")

How to terminate Infinite Loop-based Program?

1)  set a boolean variable to false:-

a = True

c=1

while a:

    print("ram")

    if c==10:

        a=False

    c=c+1    

else:

    print("Normal Termination")

2) using break statement:-

a = True

c=1

while a:

    print("ram")

    if c==10:

        break

    c=c+1    

else:

    print("Normal Termination")

3)  Check prime number using Infinite Loop?

num=5

i=2

f = True

while f:

   if num == i:

       f=False

       print("prime")

   elif num%i==0:

       print("Not Prime")

       break

      i=i+1   

Program to text to speech?

pip install pyttsx3

import time

import pyttsx3

engine = pyttsx3.init()

i=1

while i<=10:

    if i<=5:

        print(i)

        engine.say("You are in {0} Floor".format(i))

        time.sleep(1)

    else:

        print(11-i)

        engine.say("You are in {0} Floor".format(11-i))

        time.sleep(1)

        engine.runAndWait()

    i=i+1 

2)   for loop and for..else:-

using this we will print all sub statements using a single range() method. range() is used to provide starting and ending points to the process loop.

range(start, end):-   it contains two parameters first starting point and another one is the ending point.

for i in range(min,max):     #forward  increment by default 1
       statements

for i in range(max,min,-1):  #backward direction
     statement

Special cases on For Loop:-

for i in range(1,11):  # i=1; i<11; i=i+1

    print(i)

    i=i+10

    print(i)

This program will display data 10 times and increase by 1 only.

Another program of for loop to understand better

for i in range(11,1,-1):  # i=1; i<11; i=i+1

    print(i)

    i=i+10

    print(i)

...........................................................................................................

Q) WAP to print 1 to 10?
for i in range(1,11):
   print(i)
WAP to print 10 to  1?
for i in range(10,0,-1):
    print(i)
WAP to print a table of odd numbers?
num=int(input("enter number"))
if num%2!=0:
   for i in range(1,11):
      k=num*i
      print(k)
else:
    print("enter only odd number")

WAP to display fibonacci series?

#fibonacci series 0 1 1 2 3 5 8 13 21

a=-1

b=1

for i in range(1,11):

    c=a+b           #0 1 1 2 3

    print(c)

    a=b              #1

    b=c              #1

WAP to calculate factorial of any number with complete expression?

num = int(input("enter number to calculate factorial"))

f=1

s=''

for i in range(num,1,-1):  # i=num;i>1;i--

    f=f*i  #f=5 20  60 120

    s=s+str(i)+"*"

print("factorial is ",s+"1=",f)    

For..else:-

It will be executed when for loop condition will false. if we use a break statement and terminate the loop then else the statement will not work.

for i in range(min,max):

     Statements

else:

     Statements

Example of for--else

WAP to calculate the sum of one digit positive number?

sum=0

for i in range(1,10):

    sum=sum+i

else:

    print("Total is ",sum)

Another example of For--Else using break?

Run this program and analyze the output of this.

for i in range(1,11):

    print(i)

    if i==7:

        break

else:

    print("Total execution of loop is "+str(i))

Nested For Loop:-

Using this we will write more than one for loop using a nested sequence, It is a collection of Outer for loop and inner for loop.
Outer for loop will execute once and the inner for loop will be executed until the condition will false. when the outer loop condition will false then the loop program will be terminated.
for i in range(start, end):  row   or outer for loop
   for j in range(start,end):  column  or inner for loop
           Statement
          
   NewLineStatement
Solve these problems using Nested For loop:-

1 2 3 4 5

1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
...............................................................................................

1 2 3 4 5
1 2 3 4
1 2 3
1 2
1

Solution:-

for i in range(5,0,-1):

    for j in range(1,i+1):

        print(j,end=' ')

    print()    

........................................

  I  j
1   5
2   4
3   3
4   2
5   1
for i in range(1,6):
    for j in range(1,7-i):

A B C D E
A B C D
A B C
A B
A
.............................................................

A
A B
A B C
A B C D
A B C D E

.....................................
I j
1 1
2 2
3 3
4 4
5 5
for i in range(1,6):
    for j in range(1,7-i):
Assignment of Nested For Loop In Python:

1
1 2
1 2 3
1 2 3 4
1 2 3 4 5
............................................

A B C D E
a  b  c  d
A B C
a b
A
The solution to this pattern:-
for i in range(70,65,-1):
    for j in range(65,i):
        if i%2==0:
         print(chr(j),end=' ')
        else:
         print(chr(j+32),end=' ') 
    print() 

...........................................................

A  a B b C
A a B b
A a B
A a
A

The solution to this program:-
for i in range(70,65,-1):
    k=65
    for j in range(65,i):
        if j%2==0:
         print(chr(k+32),end=' ')
         k=k+1
        else:
         print(chr(k),end=' ')
       
    print() 

.........................................................

1 2 3 4 5
5 4 3 2
1 2 3
5 4
1

The solution to this pattern:-

for i in range(1,6):
    for j in range(1,7-i):
        if i%2==0:
         print(6-j,end=' ')
        else:
         print(j,end=' ') 
    print()
  ......................................................................
1 0 0 1 0
1 0 0 1
1 0 0
1 0
1
...............................................................................

The solution of This program:-
for i in range(1,6):
    a=1
    b=0
    for j in range(1,7-i):
        if j%2==0:
         print(b,end=' ')
         b=1
        else:
         print(a,end=' ')
         a=0
    print()
  Create a Pattern to print this pattern:-
A B C D E
    B C D E
        C D E
           D E
               E
The solution to this program:-

for i in range(0,5):

    ch=65

    for k in range(0,i):

        print(' ',end=' ')

        ch=ch+1

    for j in range(i,5):

        print(chr(ch),end=' ')

        ch=ch+1

            print()    

...........................................

                *

        *      *       *

*     *       *       *     *

       *       *      *

                *

Solution of this program:-

start=3

l=2 

for i in range(1,6):

    if i<=3:   

     for k in range(start,i,-1):

        print(" ",end='')

     

     for j in range(0,2*i-1):

        print("*", end='')

    else:

        

     for k in range(start,i):

        print(" ",end='')

     

     for j in range(0,2*(l)-1):

        print("*", end='')

     l=l-1   

         

    print()    

       

..............................

Infinite Loop in Python:-

This loop will continuously be executed until the condition is false. we always prefer a while loop for infinite conditions and for a loop for finite conditions.

Syntax of While Loop:-

while(true):

    Statement

Example of Simple While Loop for the infinite condition?

while True:

     print("*")

This program print infinite * symbols on the output screen

How we can convert the Infinite loop to stop mode?

We can ask user's input or last limit and convert the true condition to a false condition.

Example of this 

flag=True

i=1

while flag:

    print("*")

    i=i+1

    if i>10:

       flag=False 

    in this program, we convert the infinite loop to finite when the I value will is 10 then the loop will be automatically terminated.

Minor project work on Loop Statements?

ATM:-

WAP to manage ATM operation with the following instruction
1)  When an application will be loaded then ask for the pin code, if the pin code is correct then the process to the next phase otherwise asks pin code three times if it will be wrong then the application will be closed automatically.
 2)   If the pin code is correct then ask for operation using the menu  Press C for Credit, D for Debit, B for check balance, E for the exit, R for a Repeat operation.
3)   If the user performs three operations then automatically exit from the application.
4)  Display all log means the internal process

a hint of this program:-

flag=False

bal=5000

for i in range(1,4):

    pin = input("Enter pin code")

    if pin=="1234":

        flag=True

        break

else:

    print("Attempt completed")

while flag:

    i = input("Press C for credit,\n Press D for DEBIT \n Press E for Exit")

    if i =='c'  or i=='C':

        amount = int(input("Enter amount"))

        bal+=amount

        print(bal)

    elif i =='d' or i=='D':

        amount = int(input("Enter amount"))

        if bal>amount:

          bal-=amount

          print(bal)

        else:

           print("Insufficient balance")

    else:

        break