Program to calculate prime numbers in a given range

A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. A natural number greater than 1 that is not a prime number is called a composite number.

for example-5 is a prime number as it is divisible only by 5 and 1. 

#include<bits/stdc++.h>
#define max 1000000
//array for storing prime numbers

int a[max];
int main()

{
         int i=0;j=0;p=0;q=0;k=0,flag;
         //Enter any range

         printf("enter the range:");  

         scanf("%d %d",&p,&q);

         //loop for the whole range
          for(j=p;j<=q;j++)
              {       

                        flag=0;

                        //if number is not even then enter to next level
                        if(j%2!=0 || j==2)
                       {   

                               //check the number if it is a prime or not

                               for(i=3;i<=sqrt(j);i+=2)
                             {               
                                     if(j%i==0)
                                  {

                                         flag=1;
                                         break;

                                   }
                             }

                            //if flag=0 means j  is prime so store this into array
                            if(flag==0)
                                    a[k]=j;
                             k++;
                        }

              }

//print the array

cout<<"primes numbers are-\n";
for(i=0;i<k;i++)
cout<<a[i];
return 0;} 

OUTPUT-

Enter the range:0 10

prime numbers are-

2 3 5 7