Program to find the primes upto entered number

#include<stdio.h>

main()

{

      unsigned index, pcnt=0;

      int max;

      printf("Enter integer N upto which primes are to be find :");

      scanf("%u",&max);

      if(max>0)

      {

         printf("Prim nos. upto %u.\n",max);

         {

         for(index=1;index<=max;index++)

            if(isprime(index))      //calling the function

            {

              printf("%u\n",index);

              pcnt++;

            }

         }

      }

      printf("\nNumber of primes = %u",pcnt);

      getch();

}

//function defining here  (main is giving 1 to 10 numbers

//"if max=10 in main" for the variable num)

int isprime(unsigned num)

{

    unsigned index,sq;

      if((num==1)||(num==2)||(num==3))

      {

      return 1;     //it returns true i.e.,num=1 or num=2 or num=3

      }

    else

      sq=sqrt((double)num);

      for(index=2;index<=sq;index++)

      {

         if(num%index==0)

         return 0;   //it returns false i.e.,nothing

      }

      return 1;  //it returns true i.e.,the value of num variable

}