Nested while loop in Python programming language

Python programming language allows the use of a while loop inside another while loop, it is known as nested while loop in Python programming language

Nested while loop in Cpp programming language — Nested while loop in Python

Declaration

The syntax of the nested- while loop in Python as follows:

Syntax

while expression:             
         while expression:    
                 statement(s) 
statement(s)

Flowchat of nested while loop

Nested while loop in Python programming language — Flowchart of nested while in Python

How works nested while loop

In the nested-while loop in Python, Two type of while statements are available:

Outer while loop
Inner while loop

Initially, Outer loop test expression is evaluated only once.

When its return true, the flow of control jumps to the inner while loop. the inner while loop executes to completion. However, when the test expression is false, the flow of control comes out of inner while loop and executes again from the outer while loop only once. This flow of control persists until test expression of the outer loop is false.

Thereafter, if test expression of the outer loop is false, the flow of control skips the execution and goes to rest.

Example

Program 1

i=1
while i<=3 :
    print(i,"Outer loop is executed only once")
    j=1
    while j<=3:
        print(j,"Inner loop is executed until to completion")
        j+=1
    i+=1;

When the above code is executed, it produces the following results:

1, 'Outer loop is executed only once')
(1, 'Inner loop is executed until to completion')
(2, 'Inner loop is executed until to completion')
(3, 'Inner loop is executed until to completion')
(2, 'Outer loop is executed only once')
(1, 'Inner loop is executed until to completion')
(2, 'Inner loop is executed until to completion')
(3, 'Inner loop is executed until to completion')
(3, 'Outer loop is executed only once')
(1, 'Inner loop is executed until to completion')
(2, 'Inner loop is executed until to completion')
(3, 'Inner loop is executed until to completion')

The infinite while loop in Python

while(True):
    print("Statements of outer loop is executed only once");
    //#then flow of control enter the inner loop
    while(True):
        print("Statements of inner loop is executed until to complition");
        //#the loop executed until the execution is false
        //#this is a infinite loop

When the above code is executed, it produces the following results:

Statements of outer loop is executed only once
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
Statements of inner loop is executed until to complition
.....................
.....................

More Example for nested while loop in Python

Program 1

Display multiplication table using nested while in Python language

//#this is a program to display multiplication table
//#example for nested-while loop in Python
i=1
while i<=10:
  j=1
  while j<=12:
        print i*j,
        j+=1
  i+=1
  print "\n"

When the above code is executed, it produces the following results:

1   2  3  4  5  6  7  8  9 10 11   12 
2   4  6  8 10 12 14 16 18 20 22   24 
3   6  9 12 15 18 21 24 27 30 33   36 
4   8 12 16 20 24 28 32 36 40 44   48 
5  10 15 20 25 30 35 40 45 50 55   60 
6  12 18 24 30 36 42 48 54 60 66   72 
7  14 21 28 35 42 49 56 63 70 77   84 
8  16 24 32 40 48 56 64 72 80 88   96 
9  18 27 36 45 54 63 72 81 90 99   108 
10 20 30 40 50 60 70 80 90 100 110 120

Program 2

Display multiplication table using nested while in Python language

#this is a program to display multiplication table
#example for nested while loop in Python
i=1
while i<=5:
  j=1
  while j<=5:
        print i,"*",j,'=',i*j
        j+=1
  i+=1
  print "\n"

When the above code is executed, it produces the following results: