# C Program to find Prime Numbers

## What are Prime numbers?

Numbers which are either divisible by `1` or itself are known as Prime Numbers. For example, `11` is a prime number because it is only divisible by `1` and `11`. However, number `6` is not prime since it is divisible by `2` and `3`.

The following is a C program to print the prime numbers between `2` and `50`.

Expected Output:

## How it works:

To check for a prime number we successively divide a number `n` from `2` to `n-1`. If `n` is not divisible by any number between this range then it is a prime number.

Example 1: Is 5 a prime number?

Question Statement Result
Is 5 is divisible by 2 `5 % 2 == 0` `0` (false)
Is 5 is divisible by 3 `5 % 3 == 0` `0` (false)
Is 5 is divisible by 4 `5 % 4 == 0` `0` (false)

Hence, `5` is a prime number.

Example 2: Is 6 a prime number

Question Statement Result
Is 6 is divisible by 2 `6 % 2 == 0` `1` (true)

Number `6` is divisible by 2. Hence, it is not a prime number.

## Check Prime Numbers using a user-defined function

The following is a C program to check prime numbers using a user-defined function.

Expected Output:

1st run:

2nd run: