How to write a prime number Program in C

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

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

http://www.freebookcentre.net/programming-books-download/Computer-Programming-Fundamentals-Using-C-Part1.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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