Exercise 8 solutions

def isPrime(n):
    if n == 2:       # n is 2, the first prime
        return True
    if n < 2:        # n < 2 so not prime
        return False
    if (n % 2) == 0: # n is an even number
        return False
    # test every odd number from 3 to sqrt(n)
    i=3
    while (i <= n**(0.5)):
        if (n % i) == 0:     # after division is the remainder zero?
            return False     # if yes then it's not prime
        i = i + 2
    return True              # if we found none then it is prime

x = int(raw_input("Enter a number: "))
print "%d is prime: %r" % (x, isPrime(x))

function b = isPrime(x)

  if x == 2            % x is 2, the first prime
    b = true;
  elseif x < 2         % x < 2 so not prime
    b = false;
  elseif mod(x,2) == 0 % x is an even number
    b = false;
  else
    % test every odd number from 3 to sqrt(n)
    b = true;
    i = 3;
    while (i <= sqrt(x))
      if mod(x,i) == 0      % after division is the remainder zero?
        b = false;       % if yes then it's not prime
        return
      end
      i = i + 2;
    end
  end

x = floor(input('Enter a number: '));
disp([num2str(x), ' is prime: ',num2str(isPrime(x))]);

isPrime <- function(x) {
  if (x == 2) {         # x is 2, the first prime
      return (TRUE)
  }
  if (x < 2) {          # x < 2 so not prime
      return (FALSE)
  }
  if ((x %% 2) == 0) {  # x is an even number
      return (FALSE)
  }
  # test every odd number from 3 to sqrt(n)
  i <- 3
  while (i <= sqrt(x)) {
    if ((x %% i) == 0) {  # after division is the remainder zero?
      return (FALSE)      # if yes then it's not prime
    }
    i <- i + 2
  }
  return (TRUE)         # if we found none then it is prime
}

x <- as.integer(readline("Enter a number: "))
cat (x, "is prime:", isPrime(x), "\n")

// to compile: gcc -o e08 e08.c
//

#include <stdio.h>

int isPrime(int x) {
  if (x == 2) {
    return 1;
  }
  else if (x < 2) {
    return 0;
  }
  else if ((x % 2) == 0) {
    return 0;
  }
  int i;
  for (i=3; (i*i)<x; i+=2) {
    if ((x % i) == 0) {
      return 0;
    }
  }
  return 1;
}

int main(int argc, char *argv[]) {

  int x;
  printf("Enter a number: ");
  scanf("%d", &x);
  printf("%d is prime: %d\n", x, isPrime(x));

  return 0;
}