Write a program in c to check whether a number is prime number or not.

#include<stdio.h>
int main()
{
int num,i,flag=0;
printf("Enter a number\n");
scanf("%d",&num);
for(i=2;i<=num/2;i++)
{
if(num%i==0)
{
printf("Not a prime number");
flag=1;
break;
}
}
if(flag==0)
{
printf("prime number");
}
return 0;
}