I'll share mine also [quote]#include<stdio.h> int isPrime(int num) { int result=1; for(int i=2;i<num;i++) if(num%i==0){ result=0; break;} return result; } void main() { int yourNum; printf("Please enter a number:"); scanf("%d",&yourNum); if(!isPrime(yourNum)) printf("%d is not a prime no.\n\n",yourNum); else printf("%d is a prime no.",yourNum); }[/quote] I just shared one program that I have from our files before during our first year in college (: We almost have those kind of exercise, except about asking the password and trying to give a prompt message if it match the real one