Sunday, December 2

Program to Check Whether The Given Number is a Prime



Write a C program to check whether the given number is a prime

A prime number is a natural number that has only one and itself as factors. Examples: 2, 3, 13 are prime numbers.

Program:

#include <stdio.h>
main()
{
int n, i, c = 0;
printf("Enter any number n: \n");
scanf("%d", &n);
/*logic*/
for (i = 1; i <= n; i++)
   {
         if (n % i == 0)
              {
                  c++;
               }
    }
if (c == 2) 
   {
       printf("n is a Prime number");
    }
else 
    {
       printf("n is not a Prime number");
     }
return 0;
}


Output:
Enter any number n: 7
n is Prime
Explanation with examples:
consider a number n=5
for(i=0;i<=n;i++) /* for loop is executed until the n value equals i */
i.e. for(i=0;i<=5;i++) /* here the for loop is executed until i is equal to n */
1st iteration: i=1;i<=5;i++
here i is incremented i.e. i value for next iteration is 2
now if(n%i==0) then c is incremented
i.e.if(5%1==0)then c is incremented, here 5%1=0 thus c is incremented.
now c=1;
2nd iteration: i=2;i<=5;i++
here i is incremented i.e. i value for next iteration is 3
now if(n%i==0) then c is incremented
i.e.if(5%2==0) then c is incremented, but 5%2!=0 and so c is not incremented, c remains 1
c=1;
3rd iteration: i=3;i<=5;i++
here i is incremented i.e. i value for next iteration is 4
now if(n%i==0) then c is incremented
i.e.if(5%3==0) then c ic incremented, but 5%3!=0 and so c is not incremented, c remains 1
c=1;
4th iteration: i=4;i<=5;i++
here i is incremented i.e. i value for next iteration is 5
now if(n%i==0) then c is incremented
i.e. if(5%4==0) then c is incremented, but 5%4!=0 and so c is not incremented, c remains 1
c=1;
5th iteration: i=5;i<=5;i++
here i is incremented i.e. i value for next iteration is 6
now if(n%i==0) then c is incremented
i.e. if(5%5==0) then c is incremented, 5%5=0 and so c is incremented.
i.e. c=2
6th iteration: i=6;i<=5;i++
here i value is 6 and 6<=5 is false thus the condition fails and control leaves the for loop.
now if(c==2) then n is a prime number
we have c=2 from the 5th iteration and thus n=5 is a Prime number.