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# Nested Loops

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 in :                  for in :                            #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:     while expression:         statement(s)     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’

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