The classic problem still eludes me ... I do not know why this program is looping through up the divisor variable without stopping and going to the final "else if" ... it will identify a non prime number fine but then it loops through all of the divisors or a prime number until it becomes equal to itself and it declares it self not prime.

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) {                             // problem line :: I dont know why it always loops HERE
        divisor = divisor + 1;
        println(number + "number" + divisor + "divisor");
      } else if ( number -1 == divisor) {
        println(number + " is prime");
        is_prime = true;
      }  
    }
  }
}