Writing effecient programs

These students who have studied C in their engineering classes, will hardly write a function. They are scared of functions. I will show you how a function can make the program easier to write

#include<stdio.h>
int isPrime(int);
int main()
{
   int n;
   printf("Enter a number:");
   scanf("%d",&n);
   if (isPrime(n))
      printf("%d is prime number\n",n);
   else
      printf("%d is not a prime number \n",n);
   return 0;
}
int isPrime(int n)
{
    int i;
    for(i=2;i<i++)
      if (n%i==0)
         return 0;/* not a prime number*/
  
    return 1;/* No factor Hence prime number
}

The function returns a boolean value 1 if the number is prime and 0 if it is not. If the number as