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#### Table of Contents

**Prime Number**

A number with only two factors 1 and the number itself.

In other words, a number is divisible by only 1 and the number itself.

E.g., – 2, 3, 5, 7, 11,….

**Note:** Smallest Prime number is 2.

**Using Conditional Statement **

**Example:** Check the Prime number using a conditional statement.

` ````
```num = 4
if num <= 1:
print(num, "is not Prime Number.")
else:
for number in range(2, num):
if num % number == 0:
print(num, "is not Prime Number.")
break
else:
print(num, "is Prime Number.")

**Explanation:**

The code starts with the variable “**num**” which stores the value to be checked for the Prime number.

The condition **if num <= 1 **is used to ensure that if a **given number <= 1**, then it is not a **Prime number**.

Now, the **else condition** along with **for loop** is used to check if the given number is a Prime number or not.

**for loop** iterates over each number sequentially, starting from range **2 to num** and stored in the variable “**number**”.

The condition** num % number == 0 **checks, if the given number is divisible by each number, iterated stored in the variable “**number**” meaning that the condition is **True**.

The print() function displays the message that the given number is not a **Prime number**.

The **break **keyword is used to stop the command once the condition** num % number == 0 **is True.

If don’t use the **break **keyword, the **print()** function is displayed for each time the condition **num % number == 0 **is checked.

If the condition** num % number == 0 **is False, **else **statement is defined that uses the print() function to display the given number as a **Prime number.**

**Using Flag Variable**

**Example:** Check the Prime number using the flag variable.

` ````
```num = 30
is_prime = True
if num <= 1:
is_prime = False
else:
for number in range(2, num):
if num % number == 0:
is_prime = False
break
if is_prime:
print(num, "is Prime Number.")
else:
print(num, "is not Prime Number.")

**Explanation:**

The explanation of this example is as same as above except few points.

The code uses a flag variable as **is_prime** holds Boolean values i.e., **True** and **False**.

If the condition **num <= 1** is True, means the given number is not a Prime number since variable **is_prime** holds False.

If the condition **num <= 1** is False, which means the given number > 1, then we use the **else condition **along with for loop.

for loop iterate each number within the range **2 to num-1** and stored it in the variable “**number**”.

If the condition **num % number == 0 **is True, means the given number is not a **Prime number** because variable **is_prime** holds False.

The **break **keyword is used to stop the command once the condition** num % number == 0 **is True.

Now, we use the flag variable **is_prime** as a reference in the conditional statement to define whether the given number is a Prime number or not.

If **is_prime** is True, means **if the condition** is True, otherwise **else condition** is True.

**Using while loop**

**Example:** Check the Prime number using a while loop.

` ````
```num = 4
is_prime = True
i = 2
while i < num:
if num % i == 0:
is_prime = False
break
i += 1
if is_prime:
print(num, "is a prime number.")
else:
print(num, "is not a prime number.")

**Explanation:**

The explanation of this example is as same as above except few points.

The code starts by checking the condition **i < num, **if it is True the condition **num % i == 0 **is checked if it is divisible then the “**num**” is not a Prime number, and the command is stopped using keyword **break**.

In each loop, (i += 1) **i** value is incremented by 1.

Once the loop is terminated, meaning while the loop condition is False, the command comes to the conditional statement and uses **is_prime** as a reference to check whether the given number is Prime or not.

**Using def function**

**Example:** Check the Prime number using the def function.

` ````
```def is_prime(num):
if num <= 1:
return False
else:
for number in range(2, num):
if num % number == 0:
return False
return True
num = 17
if is_prime(num):
print(num, "is a prime number.")
else:
print(num, "is not a prime number.")

**Explanation:**

The code starts by taking the number defined as the parameter “**num**” passed to function **is_prime**.

If the condition **num <= 1**, is False returns False meaning that the given number <=1.

Now, **for loop** iterate each number within the range **2 to num-1** and stored it in the variable “**number**”.

If the condition **num % number == 0** is True, means the given number is not a Prime number and returns False.

Once the for loop is terminated, it returns True, meaning that the given number is a Prime number.

Finally, the conditional statement is checked now and displays a message using the **print()** function based on the condition.

**Conclusion**

The article provides an overview of how to determine whether a given number is prime using the Python programming language. It presents a step-by-step approach and provides a code snippet to implement the prime number-checking algorithm.