Shaddy-Ethical-hacking: A C PROGRAM TO FIND WHETHER THE GIVEN NUMBER IS PRIME OR NOT.

PRIME NUMBER :

A natural number (i.e. 1, 2, 3, 4, 5, 6, etc.) is called a prime or a prime number if it has exactly two positive divisors, 1 and the number itself.Natural numbers greater than 1 that are not prime are called composite.

Among the numbers 1 to 6, the numbers 2, 3, and 5 are the prime numbers, while 1, 4, and 6 are not prime. 1 is excluded as a prime number, for reasons explained below. 2 is a prime number, since the only natural numbers dividing it are 1 and 2. Next, 3 is prime, too: 1 and 3 do divide 3 without remainder, but 3 divided by 2 gives remainder 1. Thus, 3 is prime. However, 4 is composite, since 2 is another number (in addition to 1 and 4) dividing 4 without remainder:

4 = 2 · 2.

5 is again prime: none of the numbers 2, 3, or 4 divide 5. Next, 6 is divisible by 2 or 3, since

6 = 2 · 3.

Hence, 6 is not prime. The image at the right illustrates that 12 is not prime: 12 = 3 · 4. No even number greater than 2 is prime because by definition, any such number

n

has at least three distinct divisors, namely 1, 2, and

n

. This implies that

n

is not prime. Accordingly, the term odd prime refers to any prime number greater than 2. In a similar vein, all prime numbers bigger than 5, written in the usual decimal system, end in 1, 3, 7, or 9, since even numbers are multiples of 2 and numbers ending in 0 or 5 are multiples of 5.

THE PROGRAM IS :

#include<stdio.h>
#include<stdio.h>
int isprime(int);
int i,r,n,c=0;
void main()
{

   printf("Enter the number \n");
   scanf("%d",&n);
   r=isprime(n);
   if(r==1)
   {
       printf(" %d is a prime number \n",n);
   }
   else
   {
       printf(" %d is not a prime number \n",n);
   }
   getch();
}
   int isprime(int x)
   {
       for(i=1;i<=x;i++)
       {
           if(x%i==0)
           {
               c++;
           }
       }
       if(c==2)
       {
           return 1;
       }
       else
       {
           return 0;
       }
   }

Just copy and paste into your Microsoft Visual C++ or Turbo C (these are program developing software)

Or else you can try this demo file and use it ...

Click HERE to download this file.

(Press ctrl+z and hit Enter to end the program)..

~NOTE~ : While executing if you get any warning then just ignore it and continue with your program...

IF FACE ANY PROBLEM DON'T FORGET TO COMMENT ...!!

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