Hey again. -----------first question----------- My first question is about a program that is supposed to find prime numbers until an, user specified, max. I've used the Eratosthenes's algorithm, that consists in: - create a list of numbers since 2 to the max value; - the first number on that list is prime(2); - remove all multiples of the first number on the list(2); - do this until the last number checked is equal to the square root of the original max, the next number checked would be 3 and then 5 (4 had been removed for being a multiple of 2); Here's my source code: #include<iostream> #include<cmath> using namespace std; int main() { cout << "\t*********************************\n" << "\t**Bem vindo ao PrimeFinder v1.0" << (char) 169 << "**\n" << "\t*********************************\n\n" << "This program is protected by the universal copyright laws\n"; int allNumbers[300]; int numNumbers = 0; int max; int maxPrime; cout << "Inserir numero maximo a encontrar numeros primos (<300) -> "; cin >> max; maxPrime = sqrt(max); for(int i = 2; i <= max; ++i) allNumbers[numNumbers++] = i; for(int d = allNumbers[0]; d < maxPrime; ++d) { for(int h = 1; h <= (numNumbers-1); ++h) { if(allNumbers[h+1] % d == 0){ allNumbers[h+1] = 0; } } } cout << "Os primos ate' " << max << endl; for(int l = 0; l<(numNumbers-1); ++l) { if(allNumbers[l] == 0) continue; else cout << allNumbers[l] << endl; } system("Pause"); } Note: Just ignore the Portuguese strings. As deleting elements from an array is impossible I've associated them with an '0'. I think it all makes sense but sometimes the program also associate 5 and 7 as 0, not counting them as primes, why? -----------second question----------- I need to make a program that allows the user to "fly" an asterisk around the screen. My original idea was to create a couple of ints to hold the x and y coordinates: int xpos = 0; int ypos = 0; Then create a while(true) loop so that the program never ends; Detect the arrow keys press using the getch() function.(UP -> 72; DOWN -> 80; LEFT ->77; RIGHT -> 75) And finally use a couple of for loops(a x and a y loop) to cout a number of spaces equal to the xpos and a number of carriage returns equal to the ypos and at the end cout an asterisk...but it doesent work at all as I predicted & I can get the asterisk to move up...any ideas? Best Regards

Some minor English quibbles: I've used the Eratosthenes's algorithm, that consists in: --> which consists of create a list of numbers since 2 to the max value; --> a list of numbers from And now onto the content of the message... Note: Just ignore the Portuguese strings. Done and done. As deleting elements from an array is impossible I've associated them with an '0'. Not impossible, just a pain. I should probably point out both vectors and lists have an erase function. I think it all makes sense but sometimes the program also associate 5 and 7 as 0, not counting them as primes, why? After quickly glancing over your code, I'd say it's because the nested loops will notice that (5 % 5 == 0). I can get the asterisk to move up...any ideas? Windows implementation: #include <windows.h> void putChr(short x, short y, char c) { ::COORD pos; pos.X = x; pos.Y = y; ::SetConsoleCursorPosition(::GetStdHandle(STD_OUTPUT_HANDLE), pos); std::cout << c; } If you're using *NIX, you'll need to either use curses.h or ncurses.h.