# Python : Looping Techniques

Tutorial by:Rizwan Abdullah      Date: 2016-06-11 03:28:26

Python programming offers two kinds of loop, the for loop and the while loop. Using these loops along with loop control statements like `break` and `continue`, we can create various forms of loop.

## The infinite loop

We can create an infinite loop using `while` statement. If the condition of `while` loop is always `True`, we get an infinite loop.

### Example of infinite loop

``````
# An example of infinite loop
# press Ctrl + c to exit from the loop

while True:
num = int(input("Enter an integer: "))
print("The double of",num,"is",2 * num)``````

Output

```
Enter an integer: 3
The double of 3 is 6
Enter an integer: 5
The double of 5 is 10
Enter an integer: 6
The double of 6 is 12
Enter an integer:
Traceback (most recent call last):
```

## Loop with condition at the top

This is a normal `while` loop without `break` statements. The condition of the `while` loop is at the top and the loop terminates when this condition is `False`.

### Example

``````# Program to illustrate a loop with condition at the top

n = int(input("Enter n: "))

# initialize sum and counter
sum = 0
i = 1

while i <= n:
sum = sum + i
i = i+1    # update counter

# print the sum
print("The sum is",sum)``````

Output

```
Enter n: 10
The sum is 55
```

## Loop with condition in the middle

This kind of loop can be implemented using an infinite loop along with a conditional break in between the body of the loop.

### Example

``````# Program to illustrate a loop with condition in the middle.
# Take input from the user untill a vowel is entered

vowels = "aeiouAEIOU"

# infinite loop
while True:
v = input("Enter a vowel: ")
# condition in the middle
if v in vowels:
break
print("That is not a vowel. Try again!")

print("Thank you!")``````

Output

```
Enter a vowel: r
That is not a vowel. Try again!
Enter a vowel: 6
That is not a vowel. Try again!
Enter a vowel: ,
That is not a vowel. Try again!
Enter a vowel: u
Thank you!
```

## Loop with condition at the bottom

This kind of loop ensures that the body of the loop is executed at least once. It can be implemented using an infinite loop along with a conditional break at the end. This is similar to the `do...while` loop in C.

### Example

``````# Python program to illustrate a loop with condition at the bottom
# Roll a dice untill user chooses to exit

# import random module
import random

while True:
input("Press enter to roll the dice")

# get a number between 1 to 6
num = random.randint(1,6)
print("You got",num)
option = input("Roll again?(y/n) ")

# contion
if option == 'n':
break``````

Output

```
Press enter to roll the dice
You got 1
Roll again?(y/n) y
Press enter to roll the dice
You got 5
Roll again?(y/n) n
```

## Python

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