Question

I wanted to ask for help with the 1000th prime number problem that I am close to solving in my 5th hour of working on it. I do not know it is not dropping into the final section of the code to declare "number" as prime?

Answer 1

float number = 101.0;
float place_holder = 0;
boolean is_prime = true;
float divisor = 3.0;
//int test_number = int(ceil(sqrt(number)));

void setup() {

if (number == 0) {
println(number + " is undefined");

} else if (number > 0 && number <= 3) {
println(number + " is prime");
} else if (number % 2 == 0 && number > 2) {
println(number + " is not prime") ;
} else if (number > 2 && number % 2 !=0) {
while ( is_prime == true) {
if (number % divisor == 0) {
is_prime = false;
divisor = 3;
println(number+ " is not prime");
number = number +1;
} else if ( number % divisor !=0) { //THIS CODE RIGHT HERE IS WHERE MY PROBLEM IS
divisor = divisor + 1; //IT WONT ALLOW ME TO GO DEEPER IN THE ALOGORITHM
println(number + "number" + divisor + "divisor");
} else if ( number -1 == divisor) {
println(number + " is prime");
is_prime = true;
}
}
}
}

Answer 2

which code is this?C,C++.....

Answer 3

the processing programming language from processing.org

Answer 4

mmm where first u have a redundancy, here in the second statement with :

} else if (number > 2 && number % 2 !=0) {

well u already checked that before, u can use an else instead of evaluating 2 times the same condition.

Second u are using floatating numbers :S, primes arent natural numbers? Using operations over flotating points lead to errors in a computers, remember u CANT represent all real numbers in a computer. I think thats the problem, code seems ok for me, but i just runned it on my head xD.

There are already some algorithms to print all primes:
http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
http://en.wikipedia.org/wiki/Sieve_of_Atkin

U u can find more info here too:
http://en.wikipedia.org/wiki/Prime_number