Nested Loops

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Nested loops

Using of one loop inside another loop is called nested loop. In other words it is said as loop within the loop.

Syntax for the nested for loop

>>> for <variable> in <sequence>:

for <variable> in <sequence>:

#body goes here

The following are some of the examples of nested for loops

Ex 1 A sample program on nested for loop

for x in range(1,6):
    for y in range(x):
        print('$',end='  ')
    print("\n")

Output

$ $

$ $ $

$ $ $ $

$ $ $ $ $

For the same above example the step count is taken as “2” and is shown in below

for x in range(1,6,2):
    for y in range(x):
        print('$',end='  ')
    print("\n")

Output

$ $ $

$ $ $ $ $

Ex 2: A program to print the multiplication of ‘1’ and ’2’.

for a in range(1,3):
    for b in range(1,11):
        print("%d*%d=%d"%(a,b,a*b))

Output

1*1=1
1*2=2
1*3=3
1*4=4
1*5=5
1*6=6
1*7=7
1*8=8
1*9=9
1*10=10
2*1=2
2*2=4
2*3=6
2*4=8
2*5=10
2*6=12
2*7=14
2*8=16
2*9=18
2*10=20

Ex 3 A source code to print the pattern of numbers

x=1
for a in range(0,5):
    for b in range(5,a,-1):
        print(x,end="  ")
        x=x+1
    print()
    x=1

Output

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

Ex 4: To print the pattern of pyramid

d = 0
rows = 6
for a in range(1,rows+1):
    for b in range(1,(rows-a)+1):
        print(end="  ")
    while d != (1*a-1):
        print(" * ", end=" ")
        d = d + 1
    d = 0
    print()

Output

*
* *
* * *
* * * *
* * * * *

Ex 5 Another pattern program of nested for loops

s=5;
for i in range(s):
    for j in range(i):
        print ('* ', end="")
    print('')
for i in range(s,0,-1):
    for j in range(i):
        print('* ', end="")
    print('')

Output

*
* *
* * *
* * * *
* * * * *
* * * *
* * *
* *
*

Syntax for the nested while loop

while expression:

statement(s)

The following are some of the examples of the nested while loops

Ex 1: A sample program on nested while loop

p=2
q=4
while p<3:
    while q<6:
        print(p,",",q)
        q=q+1
        p=p+1

Output

2 , 4
3 , 5

Ex 2: To print prime numbers between 2 and 40

x=2
while(x<40):
    y=2
    while (y<=x/y):
        if not(x%y):
            break
        y=y+1
    if(y>x/y):
        print(x,"is prime")
    x=x+1
print("Executed")

Output

2 is prime
3 is prime
5 is prime
7 is prime
11 is prime
13 is prime
17 is prime
19 is prime
23 is prime
29 is prime
31 is prime
37 is prime
Executed

Ex 3: A program to print inverted right angle triangle

a = 5
b = 1
while a>0:
	while b<=5:
		print (" * "*a)
		b = b+1
		a = a-1

Output

* * * * *
* * * *
* * *
* *
*

Ex 4: A program to print the pattern of right angle triangle

a = 5
b = 1
while a>0:
	while b<=5:
		print (" * "*b)
		b = b+1
		a = a-1

Output

*
* *
* * *
* * * *
* * * * *

Ex 5: A program to print the pattern of a string “Sudha”

a = 5
b = 1
while a>0:
	while b<=5:
		print (" Sudha "*b)
		b = b+1
		a = a-1

Output

Sudha
Sudha Sudha
Sudha Sudha Sudha
Sudha Sudha Sudha Sudha
Sudha Sudha Sudha Sudha Sudha

Ex 6: Another example to print the pattern of two right angle triangles.

a = 2
while a>0:
	b = 1
	while b<=5:
		print ("*"*b)
		b = b+1
	a = a-1

Output

*
**
***
****
*****
*
**
***
****
*****

Ex 7: A program with the combination of while and for loop

s = int(input('Enter any number: '))
while s != 0:
    for t in range (1, s):
        print (t)
        t+=1
    s = int(input('Enter any number: '))

Output

Enter any number: 6
1
2
3
4
5
Enter any number: 3
1
2
Enter any number: 0

In the above example the user has to enter a number and then there prints all numbers less than that number. The process will continue until the user enters ‘0’

Example HTML page

VMS

Nested Loops

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