December 5, 2023

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# How to write a prime number Program in C

A prime number is 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.
1. Introduction
2. The logic of the Prime number in C
3. Program of Prime Number in C
4. Output
5. 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 in 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 in 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

How to Run C Program in Command Prompt

## Reference

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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