**a positive integer that is divisible only by 1 and itself**. For example: 2, 3, 5, 7, 11, 13, 17. The Prime number program is a program where we find out whether the number is prime(is greater than 1 and divided by 1 or itself) or not.

**Introduction****The logic of the Prime number in C****Program of Prime Number in C****Output****Explanation**

**Introduction **of Prime number Program

Prime number in C: A prime** number** is a number that is greater than 1 and divided by 1 or itself. In other words, prime numbers can’t be divided by other numbers than itself or 1. For example 2, 3, 5, 7, 11, 13, 17, 19, 23…. are the prime numbers.

## The logic of Prime number Program

while( y<=ep)

{

if(n%y==0)

{

z=1;

break;

}

y++;

}

if(z==0)

{

printf(“%d is a prime number”,n);

}

else

{

printf(“%d is not a prime number”,n);

}

**Program of Prime Number in C i**n Notepad

#include<stdio.h>

int main()

{

int n, y, ep, z;

printf(“Enter a number: “);

scanf(“%d”,&n);

if(n<=1)

{

printf(“%d is neither prime nor composite”);

return 0;

}

ep=n/2;

z=0;

y=2;

while( y<=ep)

{

if(n%y==0)

{

z=1;

break;

}

y++;

}

if(z==0)

{

printf(“%d is a prime number”,n);

}

else

{

printf(“%d is not a prime number”,n);

}

return 0;

}

**Output i**n cmd

D:\C Examples>prime.exe

Enter a number: 11

11 is a prime number

D:\C Examples>prime.exe

Enter a number: 9

9 is not a prime number

D:\C Examples>prime. exe

Enter a number: -1

6422288 is neither prime nor composite

D:\C Examples>prime. exe

Enter a number: 13

13 is a prime number

D:\C Examples>

## Explanation

Firstly, in the program, we have accepted the number from keyboard. As we know negative numbers and zero is not a prime number so we have put that condition that if the number is less than 1 then it is neither composite or prime. In the while loop, we have checked from 2 to ep where ep=ep/2. In the while condition, there is an if condition which checks when n is divided by y and we get 0 then z=1, which means the number is not prime. Here is the flag variable which indicates 1 or 0. If it is 1 then it is not prime and if it is 0 then it is prime.

So, the last condition is checked via if that it is prime or not.

### Click on the below link to check how we can run program in command prompt

## Reference

http://www.freebookcentre.net/Language/Free-C-Books-Download.html

## Also, read

https://curledmark.in/the-largest-number-program-in-an-array-in-c-programming/

https://curledmark.in/armstrong-number-and-arrays-in-c-programming/

https://curledmark.in/prime-reversepower-programs-in-c-programming/

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