Conditional Statements and Loops Reading Material

 

1. What are logical operators?

The logical operators are used to perform logical operations on Boolean values.
Gives

True

or

False

as a result.

Following are the logical operators

• and
• or
• not

Logical AND Operator

Gives

True

if both the booleans are true, else, it gives

False

Code

1

print(True and True)

PYTHON

Output

True

Example

Code

1

print((2 < 3) and (1 < 2))

PYTHON

Step by Step Explanation

(2 < 3) and (1 < 2)

True and (1 < 2)

True and True

Output

True

Logical OR Operator

Gives

True

if any one of the booleans is true, else, it gives

False

Code

1

print(False or False)

PYTHON

Output

False

Example

Code

1

print((2 > 3) or (2 < 1))

PYTHON

Step by Step Explanation

(2 > 3) or (2 < 1)

False or (2 < 1)

False or False

Output

False

Logical NOT Operator

Gives the opposite value of the given boolean.

Code

1

print(not(False))

PYTHON

Output

True

Example

Code

1

print(not(2 < 3))

PYTHON

Step by Step Explanation

not(2 < 3)

not(True)

False

Output

False

2. What are conditional statements?

The Conditional Statement allows you to execute a block of code based on a condition.

If statement

The Conditional Statement allows you to execute a block of code only when a specific condition is

True

.

code

1

2

3

if True:

print("If Block")

print("Inside If")

PYTHON

Output

If Block

Inside If

If-Else statement

When If-Else conditional statement is used, the Else block of code executes if the condition is

False

.

Using If-Else

Code

1

2

3

4

5

6

a = int(input())

if a > 0:

print("Positive")

else:

print("Not Positive")

print("End")

PYTHON

Input

2

Output

Positive

End

3. What are Loops?

Loops allow us to execute a block of code several times.

The loops in Python are:

• While Loop
• For Loop

4. What is the use of 

while

 loop?

While loop allows us to execute a block of code several times as long as the condition is

True

.

Example

The following code snippet prints the next three consecutive numbers after a given number.

Code

1

2

3

4

5

6

a = int(input())

counter = 0

while counter < 3:

a = a + 1

print(a)

counter = counter + 1

PYTHON

Input

4

Output

5

6

7

5. How to create a 

do-while

 loop in python?

Generally, in other programming languages, we will have another loop called the

do-while

loop.

In

do-while

loops, the code in the loop runs at least once before checking if the condition is True.

The

do-while

loop is not directly available in Python.

Example: do-while loop in c language

code

1

2

3

4

5

6

7

8

9

10

11

12

#include <stdio.h>

int main () {

int a = 1;

do {

printf("%d\n", a);

a = a + 1;

}while( a < 4 );

return 0;

}

C

Collapse

output

1

2

3

If the condition checked evaluates to True, the loop continues. For the cases where you would want your code to run at least one time then the

do-while

loops will come in handy.

do-while loop in python:

In Python, we can create a

do-while

loop by using the

while

loop to achieve similar behavior.

Code

1

2

3

4

5

6

7

i = 1

while True:

print(i)

i = i + 1

if(i > 3):

break

PYTHON

Output

1

2

3

6. What is the use of 

for

 loop?

The

for

loop is used to execute a block of code a known number of times. The

for

statement iterates over each item of a sequence.

Examples of sequences:

• The sequence of Characters (string)
• The sequence of numbers, etc.

Code

1

2

3

word = "Python"

for each_char in word:

print(each_char)

PYTHON

Output

P

y

t

h

o

n

7. What are 

range()

 and 

xrange()

 functions?

range():

The

range()

function generates a sequence of integers starting from 0 to n(n is not included) and returns it.

Syntax:

range(n)

Code

1

2

for number in range(3):

print(number)

PYTHON

Output

0

1

2

Range with Start and End

Syntax:

range(start, end)

Generates a sequence of numbers starting from

start

to

end

(

end

is not included).

Code

1

2

for number in range(5, 8):

print(number)

PYTHON

Output

5

6

7

xrange():

The

xrange()

function generates a sequence of integers starting from 0 similar to

range()

function.

Code

1

2

for number in xrange(4):

print(number)

PYTHON

Output

0

1

2

3

Note: The

xrange()

function is deprecated from Python3. You cannot run

xrange()

function in our code playground.

8. When does an infinite loop occurs?

An infinite loop occurs when the condition always evaluates to

True

i.e. incorrect termination condition.

Example

Code

1

2

3

4

a = 10

while a > 3:

a = a + 1

print(a)

PYTHON

In the above code the while loop will run infinite times as the condition always evaluates to

True

.

9. What are Nested Loops?

An inner loop within the repeating block of an outer loop is called Nested Loop.

The Inner Loop will be executed one time for each iteration of the Outer Loop.

Code

1

2

3

4

for i in range(2):

print("Outer: " + str(i))

for j in range(2):

print(" Inner: " + str(j))

PYTHON

Output

Outer: 0

Inner: 0

Inner: 1

Outer: 1

Inner: 0

Inner: 1

10. What is a break statement?/ How to exit from a loop?

Break statement makes the program exit a loop early.

Using Break

Generally,

break

is used to exit a loop when a condition is satisfied.

In the below example, when the variable

i

value equals to

3

then the

break

statement gets executed and stops the execution of the loop further.

Code

1

2

3

4

5

for i in range(5):

if i == 3:

break

print(i)

print("END")

PYTHON

Output

0

1

2

END

Break in Nested Loop

The

break

in the inner loop stops the execution of the inner loop.

Code

1

2

3

4

5

6

for i in range(4):

for j in range(4):

if i * j > 10:

break

if (i > 0) and (j > 0):

print(i * j)

PYTHON

Output

3

6

9

11. What is 

continue

 in loops?

The

continue

statement makes the program skip the remaining statements in the current iteration and begin the next iteration.

Using continue

Generally,

continue

is used to skip the remaining statements in the current iteration when a condition is satisfied.

In the below example, when the variable

i

value equals to

3

then the next statements in the loop body are skipped.

Code

1

2

3

4

5

for i in range(5):

if i == 3:

continue

print(i)

print("END")

PYTHON

Output

0

1

2

4

END

12. What is 

pass

 in Python?

The

pass

statement is a syntactic placeholder. When it is executed, nothing happens.

Generally it used when we have to test the code before writing the complete code.

Empty Loops

We can use

pass

statements to test code written so far, before writing loop logic.