C Program to check PRIME NUMBERS

main()

{

          int i,k,r,flag;

          clrscr();

          printf("ENTER THE NO. TO CHECK IT IS PRIME OR NOT: ");

          scanf("%d",&k);

          for(i=2;i<=k/2;i++)

          {

                   r=k%i;

                   if(r==0)

                             flag=0;

                   else

                             flag=1;

          }

          if(flag==1)

                   printf("THIS IS A PRIME NO.");

          else

                   printf("THIS IS NOT A PRIME NO.");

          getch();

}

OUTPUT :

 ENTER NO: 10

IT IS NOT A PRIME NO.